Difference between revisions of "Master Projects"

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The following Master thesis research projects are offered at Nikhef. If you are interested in one of these projects, please contact the coordinator listed with the project.  
 
The following Master thesis research projects are offered at Nikhef. If you are interested in one of these projects, please contact the coordinator listed with the project.  
  
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== Projects with a 2021 start ==
  
== New Projects [start in September 2018] ==
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=== ALICE: The next-generation multi-purpose detector at the LHC ===
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This main goal of this project is to focus on the next-generation multi-purpose detector planned to be built at the LHC. Its core will be a nearly massless barrel detector consisting of truly cylindrical layers based on curved wafer-scale ultra-thin silicon sensors with MAPS technology, featuring an unprecedented low material budget of 0.05% X0 per layer, with the innermost layers possibly positioned inside the beam pipe. The proposed detector is conceived for studies of pp, pA and AA collisions at luminosities a factor of 20 to 50 times higher than possible with the upgraded ALICE detector, enabling a rich physics program ranging from measurements with electromagnetic probes at ultra-low transverse momenta to precision physics in the charm and beauty sector.
  
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''Contact: [mailto:Panos.Christakoglou@nikhef.nl Panos Christakoglou] and [mailto:Alessandro.Grelli@cern.ch Alessandro Grelli] and [mailto:marco.van.leeuwen@cern.ch Marco van Leeuwen]''
  
=== The XENON Dark Matter Experiment: Data Analysis ===
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=== ALICE: Searching for the strongest magnetic field in nature ===
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In case of a non-central collision between two Pb ions, with a large value of impact parameter (b), the charged nucleons that do not participate in the interaction (called spectators) create strong magnetic fields. A back of the envelope calculation using the Biot-Savart law brings the magnitude of this filed close to 10^19Gauss in agreement with state of the art theoretical calculation, making it the strongest magnetic field in nature. The presence of this field could have direct implications in the motion of final state particles. The magnetic field, however, decays rapidly. The decay rate depends on the electric conductivity of the medium which is experimentally poorly constrained. Overall, the presence of the magnetic field, the main goal of this project, is so far not confirmed experimentally.
  
The XENON collaboration is operating the XENON1T detector, the world’s most sensitive direct detection dark matter experiment. The Nikhef group is playing an important role in this experiment. The detector operates at the Gran Sasso underground laboratory and consists of a so-called dual-phase xenon time-projection chamber filled with 3200kg of ultra-pure xenon. Our group has an opening for a motivated MSc student to do analysis with the data from this detector. The work will consist of understanding the signals that come out of the detector and applying machine learning tools to improve the reconstruction performance in our Python-based analysis tool. The final goal is to improve the signal-to-background for the dark matter search. There will also be opportunity to do data-taking shifts at the Gran Sasso underground laboratory in Italy.
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''Contact: [mailto:Panos.Christakoglou@nikhef.nl Panos Christakoglou]''
 
 
''Contact: [mailto:decowski@nikhef.nl Patrick Decowski]''
 
  
=== The Modulation Experiment: Data Analysis ===
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=== ALICE: Looking for parity violating effects in strong interactions ===
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Within the Standard Model, symmetries, such as the combination of charge conjugation (C) and parity (P), known as CP-symmetry, are considered to be key principles of particle physics. The violation of the CP-invariance can be accommodated within the Standard Model in the weak and the strong interactions, however it has only been confirmed experimentally in the former. Theory predicts that in heavy-ion collisions, in the presence of a deconfined state, gluonic fields create domains where the parity symmetry is locally violated. This manifests itself in a charge-dependent asymmetry in the production of particles relative to the reaction plane, what is called the Chiral Magnetic Effect (CME).
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The first experimental results from STAR (RHIC) and ALICE (LHC) are consistent with the expectations from the CME, however further studies are needed to constrain background effects. These highly anticipated results have the potential to reveal exiting, new physics.
  
There exist a few measurements that suggest an annual modulation in the activity of radioactive sources. With a few groups from the XENON collaboration we have developed four sets of table-top experiments to investigate this effect on a few well known radioactive sources. The experiments are under construction in Purdue University (USA), a mountain top in Switzerland, a beach in Rio de Janeiro and the last one at Nikhef in Amsterdam. We urgently need a master student to (1) analyze the first big data set, and (2) contribute to the first physics paper from the experiment. We are looking for all-round physicists with interest in both lab-work and data-analysis. The student(s) will directly collaborate with the other groups in this small collaboration (around 10 people), and the goal is to have the first physics publication ready by the end of the project. During the 2018-2019 season there are positions for two MSc students.
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''Contact: [mailto:Panos.Christakoglou@nikhef.nl Panos Christakoglou]''
  
''Contact: [mailto:z37@nikhef.nl Auke Colijn]''
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=== ALICE: Machine learning techniques as a tool to study the production of heavy flavour particles ===
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There was recently a shift in the field of heavy-ion physics triggered by experimental results obtained in collisions between small systems (e.g. protons on protons). These results resemble the ones obtained in collisions between heavy ions. This consequently raises the question of whether we create the smallest QGP droplet in collisions between small systems. The main objective of this project will be to study the production of charm particles such as D-mesons and Λc-baryons in pp collisions at the LHC. This will be done with the help of a new and innovative technique which is based on machine learning (ML). The student will also extend the studies to investigate how this production rate depends on the event activity e.g. on how many particles are created after every collision.
  
=== Theory: Stress-testing the Standard Model at the high-energy frontier ===
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''Contact: [mailto:Panos.Christakoglou@nikhef.nl Panos Christakoglou] and [mailto:Alessandro.Grelli@cern.ch Alessandro Grelli]''
  
A suitable framework to parametrise in a model-independent way deviations from the SM induced by new heavy particles is the Standard Model Effective Field Theory (SMEFT). In this formalism, bSM effects are encapsulated in higher-dimensional operators constructed from SM fields respecting their symmetry properties. Here we aim to perform a global analysis of the SMEFT from high-precision LHC data. This will be achieved by extending the NNPDF fitting framework to constrain the SMEFT coefficients, with the ultimate aim of identifying possible bSM signals.
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=== ALICE: Energy Loss of Energetic Quarks and Gluons in the Quark-Gluon Plasma ===
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One of the ways to study the quark-gluon plasma that is formed in high-energy nuclear collisions, is using high-energy partons (quarks or gluons) that are produced early in the collision and interact with the quark-gluon plasma as they propagate through it. There are several current open questions related to this topic, which can be explored in a Master's project. For example, we would like to use the new Monte Carlo generator framework JetScape to simulate collisions to see whether we can extract information about the interaction with the quark-gluon plasma. In the project you will collaborate with one of the PhD students or postdocs in our group to use the model to generate predictions of measurements and compare those to data analysis results. Depending on your interests, the project can focus more on the modeling aspects or on the analysis of experimental data from the ALICE detector at the LHC.
  
''Contact: [mailto:j.rojo@vu.nl Juan Rojo]''
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''Contact: [mailto:marco.van.leeuwen@cern.ch Marco van Leeuwen] and [mailto:marta.verweij@cern.ch Marta Verweij]''
  
=== Theory: The quark and gluon internal structure of heavy nuclei in the LHC era  ===
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=== ALICE: Extreme Rare Probes of the Quark-Gluon Plasma ===
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The quark-gluon plasma is formed in high-energy nuclear collisions and also existed shortly after the big bang.  With the large amount of data collected in recent years at the Large Hadron Collider at CERN, rare processes that previously were not accessible provide now new ways to study how the quark-gluon plasma emerges from the fundamental theory of strong interaction. One of such processes is the heavy W boson which in many cases decays to two quarks. The W boson itself doesn’t interact with the quark-gluon plasma because it doesn’t carry color, but the quark decay products do interact with the plasma and therefore provide an ideal tool to study the space-time evolution of this hot and dense medium. In this project you will use data from the ALICE detector at the LHC and simulated data from generators to study various physics mechanisms that could be happening in the real collisions.
  
A precise knowledge of the parton distribution functions (PDFs) of the proton is essential in order to make predictions for the Standard Model and beyond at hadron colliders. The presence of nuclear medium and collective phenomena which involve several nucleons modifies the parton distribution functions of nuclei (nPDFs) compared to those of a free nucleon. These modifications have been investigated by different groups using global analyses of high energy nuclear reaction world data. It is important to determine the nPDFs not only for establishing perturbative QCD factorisation in nuclei but also for applications to heavy-ion physics and neutrino physics. In this project the student will join an ongoing effort towards the determination of a data-driven model of nPDFs, and will learn how to construct tailored Artificial Neural Networks (ANNs).  
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''Contact: [mailto:marta.verweij@cern.ch Marta Verweij] and [mailto:marco.van.leeuwen@cern.ch Marco van Leeuwen]''
  
"Further information [[http://pcteserver.mi.infn.it/~nnpdf/VU/2018-MasterProject-nPDFs.pdf here]]
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=== ALICE: Jet Quenching with Machine Learning ===
  
''Contact: [mailto:j.rojo@vu.nl Juan Rojo]''
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Machine learning applications are rising steadily as a vital tool in the field of data science but are relatively new in the particle physics community. In this project machine learning tools will be used to gain insights into the modification of a parton shower in the quark-gluon plasma (QGP). The QGP is created in high-energy nuclear collisions and only lives for a very short period of time. Highly energetic partons created in the same collisions interact with the plasma while they travers it and are observed as a collimated spray of particles, known as jets, in the detector.  One of the key recent insights is that the internal structure of jets provides information about the evolution of the QGP. With data recorded by the ALICE experiment, you will use jet substructure techniques in combination with machine learning algorithms to dissect the structure of the QGP. Machine learning will be used to select the regions of radiation phase space that are affected by the presence of the QGP.
  
=== Theory: Combined QCD analysis of parton distribution and fragmentation functions ===
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''Contact: [mailto:marta.verweij@cern.ch Marta Verweij] and [mailto:marco.van.leeuwen@cern.ch Marco van Leeuwen]''
  
The formation of hadrons from quarks and gluons, or collectively partons, is a fundamental QCD process that has yet to be fully understood. Since parton-to-hadron fragmentation occurs over long-distance scales, such information can only be extracted from experimental observables that identify mesons and baryons in the final state. Recent progress has been made to determine these fragmentation functions (FFs) from charged pion and kaon production in single inclusive e+e−-annihilation (SIA) and additionally pp-collisions and semi-inclusive deep inelastic scattering (SIDIS). However, charged hadron production in unpolarized pp and inelastic lepton-proton scattering also require information about the momentum distributions of the quarks and gluons in the proton, which is encoded in non-perturbative parton distribution functions (PDFs). In this project, a simultaneous treatment of both PDFs and FFs in a global QCD analysis of single inclusive hadron production processes will be made to determine the individual parton-to-hadron FFs. Furthermore, a robust statistical methodology with an artificial neural network learning algorithm will be used to obtain a precise estimation of the FF uncertainties. This work will emphasis in particular the impact of pp-collision and SIDIS data on the gluon and separated quark/anti-quark FFs, respectively.
 
  
"Further information [[http://pcteserver.mi.infn.it/~nnpdf/VU/2018-MasterProject-FFpPDFs.pdf here]]
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=== ATLAS: Top Spin and EFTs in the Wtb vertex ===
  
''Contact: [mailto:j.rojo@vu.nl Juan Rojo]''
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The top quark has an exceptional high mass, close to the electroweak symmetry breaking scale and therefore sensitive to new physics effects. Theoretically, new physics is well described in the EFT framework [1]. The (EFT) operators are experimentally well accessible in single top t-channel production where the top quark is produced spin polarized. The focus at Nikhef is the operator O_{tW} with a possible imaginary phase, leading to CP violation. Experimentally, many angular distribution are reconstructed in the top rest frame to hunt for these effects.  There are several challenging analysis-topics for master students, which can also be tailored a bit your interests:
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1) MC study EFT effects from background substraction.
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2) NLO reweighting (as function of EFT parameters)  based on Madgraph
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3) Kinematic Fitter neural network estimation vs analytic as available
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4) Pt dependent analysis of existing analysis
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5) Make a combination with a higgs channel? (difficult)
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6) Make a combination with other top channels? (difficult)
  
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More info in this presentation:
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www.nikhef.nl/~h73/top_masterstudenten_mrt2021.pptx
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and/or in the video:
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https://video.uva.nl/media/t/0_0f2fuazf
  
=== ALICE: Charm is in the Quark Gluon Plasma ===
 
The goal of heavy-ion physics is to study the Quark Gluon Plasma (QGP), a hot and dense medium where quarks and gluons move freely over large distances, larger than the typical size of a hadron. Hydrodynamic simulations expect that the QGP will expand under its own pressure, and cool while expanding. These simulations are particularly successful in describing some of the key observables measured experimentally, such as particle spectra and various orders of flow harmonics. Charm quarks are produced very early during the evolution of a heavy-ion collision and can thus serve as an idea probe of the properties of the QGP. The goal of the project is to study higher order flow harmonics (e.g. triangular flow - v3) that are more sensitive to the transport properties of the QGP for charm-mesons, such as D0, D*, Ds. This will be the first ever measurement of this kind.
 
  
''Contact: [mailto:Panos.Christakoglou@nikhef.nl Panos Christakoglou and Paul Kuijer]''
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[1] https://arxiv.org/abs/1807.03576
  
=== ALICE: Probing the time evolution of particle production in the Quark-Gluon Plasma ===
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''Contact: Marcel Vreeswijk [mailto:h73@nikhef.nl] and Jordy Degens [mailto:jdegens@nikhef.nl]  ''
Particle production is governed by conservation laws, such as local charge conservation. The latter ensures that each charged particle is balanced by an oppositely-charged partner, created at the same location in space and time. The charge-dependent angular correlations, traditionally studied with the balance function, have emerged as a powerful tool to probe the properties of the Quark-Gluon Plasma (QGP) created in high energy collisions. The goal of this project is to take full advantage of the unique, among all LHC experiments, capabilities of the ALICE detector that is able to identify particles to extend the studies to different particle species (e.g. pions, kaons, protons…). These studies are highly anticipated by both the experimental and theoretical communities.
 
  
''Contact: [mailto:Panos.Christakoglou@nikhef.nl Panos Christakoglou]''
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=== ATLAS: The Next Generation ===
  
=== ALICE: CP violating effects in QCD: looking for the chiral magnetic effect with ALICE at the LHC ===
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After the observation of the coupling of Higgs bosons to fermions of the third generation, the search for the coupling to fermions of the second generation is one of the next priorities for research at CERN's Large Hadron Collider. The search for the decay of the Higgs boson to two charm quarks is very new [1] and we see various opportunities for interesting developments. For this project we propose improvements in reconstruction (using exclusive decays), advanced analysis techiques (using deep learning methods) and expanding the theory interpretation. Another opportunity would be the development of the first statistical combination of results between the ATLAS and CMS experiment, which could significantly improve the discovery potentional.
Within the Standard Model, symmetries, such as the combination of charge conjugation (C) and parity (P), known as CP-symmetry, are considered to be key principles of particle physics. The violation of the CP-invariance can be accommodated within the Standard Model in the weak and the strong interactions, however it has only been confirmed experimentally in the former. Theory predicts that in heavy-ion collisions gluonic fields create domains where the parity symmetry is locally violated. This manifests itself in a charge-dependent asymmetry in the production of particles relative to the reaction plane, which is called Chiral Magnetic Effect (CME). The first experimental results from STAR (RHIC) and ALICE (LHC) are consistent with the expectations from the CME, but background effects have not yet been properly disentangled. In this project you will develop and test new observables of the CME, trying to understand and discriminate the background sources that affects such a measurement.  
 
  
''Contact: [mailto:Panos.Christakoglou@nikhef.nl Panos Christakoglou]''
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[1] https://arxiv.org/abs/1802.04329
  
=== ALICE: Particle polarisation in strong magnetic fields ===
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''Contact: [mailto:tdupree@nikhef.nl Tristan du Pree]''
When two atomic nuclei, moving in opposite directions, collide off- center then the Quark Gluon Plasma (QGP) created in the overlap zone is expected to rotate. The nucleons not participating in the collision represent electric currents generating an intense magnetic field. The magnetic field could be as large as 10^{18} gauss, orders of magnitude larger than the strongest magnetic fields found in astronomical objects. Proving the existence of the rotation and/or the magnetic field could be done by checking if particles with spin are aligned with the rotation axis or if charged particles have different production rates relative to the direction of the magnetic field. In particular, the longitudinal and transverse polarisation of the Lambda^0 baryon will be studied. This project requires some affinity with computer programming.  
 
  
''Contact: [mailto:Paul.Kuijer@nikhef.nl Paul Kuijer]''
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=== ATLAS: The Most Energetic Higgs Boson ===
  
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The production of Higgs bosons at the highest energies could give the first indications for deviations from the standard model of particle physics, but production energies above 500 GeV have not been observed yet [1]. The LHC Run-2 dataset, collected during the last 4 years, might be the first opportunity to observe such processes, and we have various ideas for new studies. Possible developments include the improvement of boosted reconstruction techniques, for example using multivariate deep learning methods. Also, there are various opportunities for unexplored theory interpretations (using the MadGraph event generator), including effective field theory models (with novel ‘morphing’ techniques) and new interpretations of the newly observed boosted VZ(bb) process.
  
=== ATLAS : Excited lepton searches with multiple leptons ===
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[1] https://arxiv.org/abs/1709.05543
  
The Standard Model of particle physics (SM) is extremely successful, but would it hold against check with data containing multiple leptons? Although very rare process, the production of leptons is calculated in SM with high precision. On detector side the leptons (electrons and muons) are easy to reconstruct and such a sample contains very little "non-lepton" background. This analysis has an ambitious goal to find beyond Standard Model processes like Excited leptons using events with 4 leptons.  With this project, the student would gain close familiarity with modern experimental techniques (statistical analysis, SM predictions, search for rare signals), with Monte Carlo generators and the standard HEP analysis tools (ROOT, C++, python).
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''Contact: [mailto:tdupree@nikhef.nl Tristan du Pree]''
  
''Contact: [mailto:O.Igonkina@nikhef.nl Olya Igonkina and Marcus Morgenstern and Pepijn Bakker]''
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=== ATLAS: Searching for new particles in very energetic diboson production ===
  
=== ATLAS : A search for lepton flavor violation with tau decays ===
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The discovery of new phenomena in high-energy proton–proton collisions is one of the main goals of the Large Hadron Collider (LHC). New heavy particles decaying into a pair of vector bosons (WW, WZ, ZZ) are predicted in several extensions to the Standard Model (e.g. extended gauge-symmetry models, Grand Unified theories, theories with warped extra dimensions, etc). In this project we will investigate new ideas to look for these resonances in a region that is yet unexplored in the data. We will focus on the final states where both vector bosons decay into quarks as they are expected to bring the highest sensitivity [1]. We will try to reconstruct and exploit the polarisation of the vector bosons (using machine learning methods) and then tackle the problem of estimating contributions from beyond the Standard Model processes in the tails of the mass distribution.
  
Quarks mix, neutrinos mix, charged leptons do not mix. Why? Is that really how the nature works, or is it just a limitation in our detection techniques. ATLAS has recorded now a huge sample of data. Even such difficult final states as tau->3mu become accessible. However, the decays of charm and beauty mesons could spoil the picture with decays that resembles the signal. The goal of the project is to understand what
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[1] https://arxiv.org/abs/1906.08589
background decays are present and to find a way to suppress them. Success of project will allow much higher sensitivity to beyond Standard Model physics of tau->3mu. The student would gain close familiarity with modern experimental techniques (statistical analysis, SM predictions, search for rare signals), background suppression techniques and the standard HEP analysis tools (ROOT, C++, python).
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''Contact: [mailto:f.dias@nikhef.nl Flavia de Almeida Dias]''
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=== ATLAS R&D: Study of LGAD sensors ===
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The Atlas detector has been installed more than a decade ago. Several upgrades of the detector are being worked on that will adapt the ATLAS experiment to the so-called High Luminosity LHC. A new (sub)detector that will be installed and become part of the Atlas detector is the High-Granularity Timing Detector (HGTD) detector. The HGTD will measure very precisely the passage time of particles in the detector and will help identify from which of the plurious proton-proton collisions the particle originates from. The HGTD is partly made of LGAD sensors. These are granulated silicon sensors dedicatedly designed for the HGTD. In this project we will characterise the LGAD sensors.
  
''Contact: [mailto:O.Igonkina@nikhef.nl Olya Igonkina and Edwin Chow]''
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''Contact: [mailto:f.dias@nikhef.nl Hella Snoek]''
  
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===LHCb: Measuring differences between electrons and muons, beyond the Standard Model===
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A current “hot topic” in the field of particle physics is the potential violation of lepton-universality.
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At the LHCb experiment, lepton-universality tests are performed by looking at the ratio of decays
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into muons and into electrons/taus. Recent measurements in meson modes show hints (2 ? 3?) of lepton non-universality.
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Baryonic modes, however, have been less studied and provide an independent test of lepton-universality.
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At Nikhef, we study the decay Lambdab->Lambda l+l- , where l can be an electron or a muon.
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There are two possible project topics:
  
=== ATLAS : A search for lepton non-universality in Bc meson decays ===
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1. Identifying novel analysis techniques in the high di-lepton invariant mass region. Electrons in this region undergo more Bremsstrahlung, and therefore have a worse momentum resolution,
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meaning background from the resonant Psi(2S) mode can leak into our signal. Since we expect most of our signal in this region, it is important to improve this, most likely using machine learning techniques.
  
Recently, LHCb experiment has reported a number of intriguing deviations from SM in leptonic decays of B mesons. With this project we would like to probe if ATLAS also observes the same kind of deviation, e.g. in Bc->Jpsi+tau+nu channel w.r.t BC->Jpsi+mu+nu. Success of project will be essential to understand if we finally observe  beyond SM process or if LHCb has some detector bias. The student would gain close familiarity with modern experimental techniques (statistical analysis, SM predictions, search for rare signals), background suppression techniques and the standard HEP analysis tools (ROOT, C++, python).
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2. Identifying, simulating, and setting up a rejection for partially reconstructed Lambdab->Lambda* l+l- backgrounds. By not fully reconstructing the excited Lambda*0, we can mis-reconstruct it as a signal
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candidate. Machine learning techniques could be explored.
  
''Contact: [mailto:O.Igonkina@nikhef.nl Olya Igonkina and Edwin Chow]''
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''Contact: [mailto:l.greeven@nikhef.nl Lex Greeven] and [mailto:h71@nikhef.nl Niels Tuning]''
  
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===LHCb: New physics in the angular distributions of B decays to K*ee===
  
=== LHCb: Searching for dark matter in exotic six-quark particles ===
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Lepton flavour violation in B decays can be explained by a variety of non-standard model interactions. Angular distributions in decays of a B meson to a hadron and two leptons are an important source of information to understand which model is correct. Previous analyses at the LHCb experiment have considered final states with a pair of muons. Our LHCb group at Nikhef concentrates on a new measurement of angular distributions in decays with two electrons. The main challenge in this measurement is the calibration of the detection efficiency. In this project you will confront estimates of the detection efficiency derived from simulation with decay distributions in a well known B decay. Once the calibration is understood, the very first analysis of the angular distributions in the electron final state can be performed.  
3/4 of the mass in the Universe is of unknown type. Many hypotheses about this dark matter have been proposed, but none confirmed. Recently it has been proposed that it could be made of particles made of the six quarks uuddss. Such a particle could be produced in decays of heavy baryons. It is proposed to use Xi_b baryons produced at LHCb to search for such a state. The latter would appear as missing 4-momentum in a kinematically constrained decay. The project consists in optimising a selection and applying it to LHCb data. See [https://arxiv.org/abs/1708.08951 arXiv:1708.08951]
 
  
''Contact: [mailto:patrick.koppenburg@cern.ch Patrick Koppenburg]''
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Contact: [mailto:wouterh@nikhef.nl Wouter Hulsbergen] and [mailto:m.senghi.soares@nikhef.nl Mara Soares]
  
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===LHCb: Discovering heavy neutrinos in B decays===
  
=== LHCb: Measurement of BR(B0 → Ds+ Ds-) ===
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Neutrinos are the lightest of all fermions in the standard model. Mechanisms to explain their small mass rely on the introduction of new, much heavier, neutral leptons. If the mass of these new neutrinos is below the b-quark mass, they can be observed in B hadron decays.
  
This project aims to discover the branching fraction of the decay B0->Ds- Ds+. The decay B0->Ds- Ds+ is quite rare, because it occurs through the exchange of a W-boson between the b and the d-quark of the B0-meson. This decay proceeds via Cabibbo-suppressed W-exchange and has not yet been observed; theoretical calculations predict a branching fraction at the order of 10^-5 with a best experimental upper limit of 3.6x10^-5.
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In this project we search for the decay of B+ mesons in into an ordinary electron or muon and the yet undisovered heavy neutrino. The heavy neutrino is expected to be unstable and in turn decay quickly into a charged pion and another electron or muon. The final state in which the two leptons differ in flavour, "B+ to e mu pi", is particularly interesting: It is forbidden in the standard model, such that backgrounds are small. The analysis will be performed within the LHCb group at Nikhef using LHCb run-2 data.
A measurement of the decay rate of B0 -> Ds+Ds- relative to that of B0 -> D+D- can provide an estimate of the W-exchange contribution to the latter decay, a crucial piece of information for extracting the CKM angle gamma from B0 -> D(*)D(*).
 
The aim is to determine the relative branching fraction of B0->Ds+Ds- with respect to B0->Ds+D- decays (which has the best known branching ratio at present, (7.2 +- 0.8)x10^-3), in close collaboration with the PhD. The aim is that this project results in a journal publication on behalf of the LHCb collaboration. For this project computer skills are needed. The ROOT programme and C++ and/or Python macros are used. This is a project that is closely related to previous analyses in the group. Weekly video meetings with CERN coordinate the efforts with in the LHCb collaboration.
 
Relevant information:
 
[1] M.Jung and S.Schacht, "Standard Model Predictions and New Physics Sensitivity in B -> DD Decays" https://arxiv.org/pdf/1410.8396.pdf
 
[2] L.Bel, K.de Bruyn, R. Fleischer, M.Mulder, N.Tuning, "Anatomy of B -> DD Decays" https://arxiv.org/pdf/1505.01361.pdf
 
[3] A.Zupanc et al [Belle Collaboration] "Improved measurement of B0 -> DsD+ and search for B0 -> Ds+Ds at Belle" https://arxiv.org/pdf/hep-ex/0703040.pdf
 
[4] B.Aubert et al. [Babar Collaboration] "Search for the W-exchange decays B0 -> DD+" https://arxiv.org/pdf/hep-ex/0510051.pdf
 
[5] R.Aaij et al. [LHCb Collaboration], "First observations of B0s -> D+D, Ds+D and D0D0 decays" https://arxiv.org/pdf/1302.5854.pdf
 
  
''Contact: [mailto:niels.tuning@nikhef.nl Niels Tuning], [mailto:m.veronesi@nikhef.nl Michele Veronesi (PhD)], [mailto:s.esen@nikhef.nl Sevda Esen (postdoc)]''
 
  
=== LHCb: Measurement of relative ratio of B+ → D0D+ and B+ → D0Ds decays ===
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''Contact: [mailto:v.lukashenko@nikhef.nl Lera Lukashenko] and''  [mailto:wouterh@nikhef.nl Wouter Hulsbergen]
  
This decay is closely related to B0->Ds- Ds+ (see above), and close collaboration between the two master projects is foreseen. The decay mode B+->D0D+ is expected to be dominated by tree diagrams with some additional contributions from penguin diagrams. Assuming SU(3) symmetry, measurement of its branching fraction relative to Cabibbo-favored B+->D0D will enable better understanding of penguin contributions to the CP violating mixing phase.
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===LHCb: Searching for dark matter in exotic six-quark particles ===
Relevant information:
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3/4 of the mass in the Universe is of unknown type. Many hypotheses about this dark matter have been proposed, but none confirmed. Recently it has been proposed that it could be made of particles made of the six quarks uuddss. Such a particle could be produced in decays of heavy baryons. It is proposed to use Xi_b baryons produced at LHCb to search for such a state. The latter would appear as missing 4-momentum in a kinematically constrained decay. The project consists in optimising a selection and applying it to LHCb data. See [https://arxiv.org/abs/1708.08951 arXiv:1708.08951]
[1] L.Bel, K.de Bruyn, R. Fleischer, M.Mulder, N.Tuning, "Anatomy of B -> DD Decays" https://arxiv.org/pdf/1505.01361.pdf
 
[2] R.Aaij et al. [LHCb Collaboration], "First observations of B0s -> D+D, Ds+D and D0D0 decays" https://arxiv.org/pdf/1302.5854.pdf
 
[3] PDG: http://pdglive.lbl.gov/BranchingRatio.action?desig=261&parCode=S041
 
  
''Contact: [mailto:niels.tuning@nikhef.nl Niels Tuning], [mailto:m.veronesi@nikhef.nl Michele Veronesi (PhD)], [mailto:s.esen@nikhef.nl Sevda Esen (postdoc)]''
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''Contact: [mailto:patrick.koppenburg@cern.ch Patrick Koppenburg]''
  
=== Virgo: Searching for gravitational waves from compact binary coalescence ===
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===With the Dark Matter group: Fine structure constant===
 +
The fine-structure constant has been measured by many experiments in the past and it is one of the most precisely known constants in nature. The goal of this project is to design and build an experiment to do an in-house measurement of the fine structure constant by investigating positron annihilation to two and to three photons. The work within this project encompasses the full breadth of experimental physics: from a conceptual design to the final analysis of the data. In addition, there is a budget of 10kEuro available to purchase the necessary hardware for the project. Supervision will be done by Colijn and the Nikhef director Bentvelsen.
  
Matched-filter searches for gravitational-wave signals from binary neutron stars, binary black holes and neutron-star-black-hole systems have been successful but many simplifications have been made. There are a number of avenues to explore for research, including expanding the parameter space to include precessing binaries or intermediate-mass black hole binaries, implementing multivariate statistics with analytic and machine learning techniques, and developing deeper searches by coordinating with gamma-ray triggers. These projects will include development work (python, C) and will be implemented in the upcoming Virgo/LIGO science runs, potentially leading to new discoveries and physics.
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''Contact: [mailto:colijn@nikhef.nl Auke-Pieter Colijn]''
  
''Contact: [mailto:caudills@nikhef.nl Sarah Caudill]''
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===Dark Matter: Sensitive tests of wavelength-shifting properties of materials for dark matter detectors===
 +
Rare event search experiments that look for neutrino and dark matter interactions are performed with highly sensitive detector systems, often relying on scintillators, especially liquid noble gases, to detect particle interactions. Detectors consist of structural materials that are assumed to be optically passive, and light detection systems that use reflectors, light detectors, and sometimes, wavelength-shifting materials. MSc theses are available related to measuring the efficiency of light detection systems that might be used in future detectors. Furthermore, measurements to ensure that presumably passive materials do not fluoresce, at the low level relevant to the detectors, can be done. Part of the thesis work can include Monte Carlo simulations and data analysis for current and upcoming dark matter detectors, to study the effect of different levels of desired and nuisance wavelength shifting. In this project, students will acquire skills in photon detection, wavelength shifting technologies, vacuum systems, UV and extreme-UV optics, detector design, and optionally in C++ programming, data analysis, and Monte Carlo techniques.
  
=== Virgo: Simulations of Binary Neutron Star Mergers and applications for multimessenger astronomy ===
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''Contact: [mailto:Tina.Pollmann@tum.de Tina Pollmann] and [mailto:decowski@nikhef.nl Patrick Decowski]''
  
With the detection of the binary neutron star merger in August 2017 (GW170817) a new era of multi-messenger astronomy started. GW170817 proved that neutron star mergers are ideal laboratories to constrain the equation of state of cold supranuclear matter, to study the central engines of short GRBs, and to understand the origin and production of heavy elements.
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=== Dark Matter: Building better Dark Matter Detectors - the XAMS  R&D Setup===
The fundamental tool to understand the last stages of the binary dynamics are numerical relativity simulations. In this project the student will be introduced to the basics of numerical relativity simulations of binary neutron star simulations and will be able to perform simulations on its own. Based on these simulations and the first experience it will be possible to focus on one of the following aspects:
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The Amsterdam Dark Matter group operates an R&D xenon detector at Nikhef. The detector is a dual-phase xenon time-projection chamber and contains about 4kg of ultra-pure liquid xenon. We use this detector for the development of new detection techniques - such as utilizing our newly installed silicon photomultipliers - and to improve the understanding of the response of liquid xenon to various forms of radiation. The results could be directly used in the XENONnT experiment, the world’s most sensitive direct detection dark matter experiment at the Gran Sasso underground laboratory, or for future Dark Matter experiments like DARWIN. We have several interesting projects for this facility. We are looking for someone who is interested in working in a laboratory on high-tech equipment, modifying the detector, taking data and analyzing the data him/herself. You will "own" this experiment.  
  
- the estimation of the ejected material released from the merger and the development of models for the electromagnetic signals
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''Contact: [mailto:decowski@nikhef.nl Patrick Decowski] and [mailto:z37@nikhef.nl Auke Colijn]''
  
- further improvement of gravitational waveform models including numerical relativity information
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===Dark Matter: Searching for Dark Matter Particles - XENONnT Data Analysis ===
 +
The XENON collaboration has used the XENON1T detector to achieve the world’s most sensitive direct detection dark matter results and is currently starting the XENONnT successor experiment. The detectors operate at the Gran Sasso underground laboratory and consist of so-called dual-phase xenon time-projection chambers filled with ultra-pure xenon. Our group has an opening for a motivated MSc student to do analysis with the new data coming from the XENONnT detector. The work will consist of understanding the detector signals and applying a deep neural network  to improve the (gas-) background discrimination in our Python-based analysis tool to improve the sensitivity for low-mass dark matter particles. The work will continue a study started by a recent graduate.  There will also be opportunity to do data-taking shifts at the Gran Sasso underground laboratory in Italy.
  
- further improvement of the construction of the initial conditions of binary neutron star simulations
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''Contact: [mailto:decowski@nikhef.nl Patrick Decowski] and [mailto:z37@nikhef.nl Auke Colijn]''
  
- code improvements of the evolution code incorporating additional microphysical aspects as magnetic fields, tabulated equation of states, or neutrino leakage schemes.
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===Dark Matter: The Ultimate Dark Matter Experiment - DARWIN Sensitivity Studies===
 +
DARWIN is the “ultimate” direct detection dark matter experiment, with the goal to reach the so-called “neutrino floor”, when neutrinos become a hard-to-reduce background. The large and exquisitely clean xenon mass will allow DARWIN to also be sensitive to other physics signals such as solar neutrinos, double-beta decay from Xe-136, axions and axion-like particles etc. While the experiment will only start in 2027, we are in the midst of optimizing the experiment, which is driven by simulations. We have an opening for a student to work on the GEANT4 Monte Carlo simulations for DARWIN, as part of a simulation team together with the University of Freiburg and Zurich. We are also working on a “fast simulation” that could be included in this framework. It is your opportunity to steer the optimization of a large and unique experiment. This project requires good programming skills (Python and C++) and data analysis/physics interpretation skills.
 +
''Contact: [mailto:decowski@nikhef.nl Patrick Decowski] and [mailto:z37@nikhef.nl Auke Colijn]''
  
- studying the merger properties of neutron stars with exotic objects as boson or axion stars.  
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===Detector R&D: Test beam with a bent ALPIDE monolithic active pixel sensor===
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The next ALICE inner tracking system that is to be installed in 2025 at the large hadron collider (LHC) will feature ultrathin silicon monolithic active pixel sensors (MAPS). The current ALICE tracking system that has just been installed already features this new, very thin pixel detectors with low noise and low power consumption, but for the next tracker they will be bent around the beam pipe. In this project, you will be part of the international ALICE collaboration. You will analyze data from beam tests performed at CERN and DESY to characterize bent pixel detectors. You will be part of the Nikhef R&D group and will also have the opportunity to perform your own measurements in the lab on the ALICE pixel detector (ALPIDE) or on an even thinner version thereof. If the travel situation allows, you will have the opportunity to join the ALICE test beam group in Hamburg at DESY to take part in the exciting experience of taking real data.
 +
''Contact: [mailto:jory.sonneveld@nikhef.nl Jory Sonneveld]''
  
''Contact: [mailto:diettim@nikhef.nl Tim Dietrich]''
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===Detector R&D: Modeling radiation damage for the next generation ATLAS pixel detector===
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In 2026 the ATLAS tracker will be upgraded to the largest silicon tracker in the world. This tracker will have to cope with very large data rates foreseen in the upgraded high luminosity large hadron collider (HL-LHC). From then on, this tracker will see very high rates of radiation, particularly in the inner tracker closest to the LHC beam line. In this project you will evaluate the performance of the silicon pixel sensors for the new ATLAS inner tracker. You will learn to use commercial technology computer aided design software (TCAD) for modeling semiconductors widely used in the semiconductor industry and compare your simulation results with data from the beam tests performed on the new modules for ATLAS ITk at CERN. You will also use and develop fast simulation tools like Allpix Squared for which you will use your C++ programming skills. As a member of the international ATLAS collaboration you will present your work in an international environment, and you will be part of the Nikhef detector R&D group where you will learn about the newest fast timing silicon detector technologies for LHC experiments and beyond.
 +
''Contact: [mailto:jory.sonneveld@nikhef.nl Jory Sonneveld]''
  
=== Virgo: Measuring cosmological parameters from gravitational-wave observations of compact binaries ===
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===Detector R&D: Characterisation of Trench Isolated Low Gain Avalanche Detectors (TI-LGAD) ===
 +
The future vertex detector of the LHCb Experiment needs to measure the spatial coordinates and time of the particles originating in the LHC proton-proton collisions with resolutions better than 10 um and 50 ps, respectively. Several technologies are being considered to achieve these resolutions.  Among those is a novel sensor  technology called Trench Isolated Low Gain Avalanche Detector.
 +
Prototype pixelated sensors have been manufactured recently and have to be characterised. Therefore these new sensors will be bump bonded to a Timepix4 ASIC which provides charge and time measurements in each of 230 thousand pixels. Characterisation will be done using a lab setup at Nikhef, and includes tests with a micro-focused laser beam, radioactive sources, and possibly with particle tracks obtained in a test-beam.  This project involves data taking with these new devices and analysing the data to determine the performance parameters such as the spatial and temporal resolution. as function of temperature and other operational conditions.
  
Gravitational wave observation of the binary neutron star merger GW170817 with its coincident optical counterpart led to a first "standard siren" measurement of the Hubble parameter independent of the cosmological distance ladder. While multiple similar observations are expected to improve the precision of the measurement, a statistical method of cross correlation with galaxy catalogues of gravitational-wave distance estimates is expected to work even without identified electromagnetic transients, and for binary black hole mergers in particular. The project would primarily be a study of various systematic effects in this analysis and correcting for them. The work will involve use of computational techniques to analyze LIGO-Virgo data. Some prior experience of programmimg is expected.
+
''Contacts: [mailto:kazu.akiba@nikhef.nl Kazu Akiba] and [mailto:martinb@nikhef.nl Martin van Beuzekom]''
  
''Contact: [mailto:archis@nikhef.nl Archisman Ghosh] and [mailto:vdbroeck@nikhef.nl Chris Van Den Broeck]''
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=== Detector R&D: Studying fast timing detectors===
 +
Fast timing detectors are the solution for future tracking detectors. In future LHC operation conditions and future colliders, more and more particles are produced per collision. The high particle densities make it increasingly more difficult to separate particle trajectories with the spatial information that current silicon tracking detectors provide. A solution would be to add very precise (in order of 10ps) timestamps to the spatial measurements of the particle trackers. A good understanding of the performance of fast timing detectors is necessary. With the user of a pulsed laser in the lab we study the characteristics of several prototype detectors.
  
=== Detector R&D: Spectral X-ray imaging - Looking at colours the eyes can't see ===
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''Contact: [mailto:hella.snoek@.nl Hella Snoek] or [mailto:kazu.akiba@nikhef.nl Kazu Akiba]''
 +
===Detector R&D: Laser Interferometer Space Antenna (LISA) - Wavefront sensors for gravitational wave detection===
 +
The space-based gravitational wave antenna LISA is one of the most challenging space missions ever proposed. ESA plans to launch around 2030 three spacecraft separated by a few million kilometres. This constellation measures tiny variations in the distances between test-masses located in each satellite to detect gravitational waves from sources such as supermassive black holes. LISA is based on laser interferometry, and the three satellites form a giant Michelson interferometer. LISA measures a relative phase shift between one local laser and one distant laser by light interference. The phase shift measurement requires sensitive wavefront sensors. The Nikhef DR&D group fabricated prototype sensors in 2020 together with the Photonics industry and the Dutch institute for space research SRON. As an MSc student, you will work on various aspects of the wavefront sensor development: study the performance of the epitaxial stacks of Indium-Gallium-Arsenide, setting up test benches to characterize the sensors, and performing the actual tests and data analysis.
  
When a conventional X-ray image is made to analyse the composition of a sample, or to perform a medical examination on a patient, one acquires an image that only shows intensities. One obtains a ‘black and white’ image. Most of the information carried by the photon energy is lost. Lacking spectral information can result in an ambiguity between material composition and amount of material in the sample. If the X-ray intensity as a function of the energy can be measured (i.e. a ‘colour’ X-ray image) more information can be obtained from a sample. This translates to less required dose and/or to a better understanding of the sample that is being investigated. For example, two fields that can benefit from spectral X-ray imaging are mammography and real time CT.
+
''Contact: [mailto:nielsvb@nikhef.nl Niels van Bakel]''
  
X-ray detectors based on Medipix/Timepix pixel chips have spectral resolving capabilities and can be used to make polychromatic X-ray images. Medipix and Timepix chips have branched from pixel chips developed for detectors for high energy physics collider experiments.
+
===Detector R&D: Time tracking Cosmic rays===
 +
One of the main challenges in particle physics detector technologies is to perform precise time measurements while maintaining, or even improving, the excellent spatial resolution. New sensor prototypes need to be characterised using charged particles in order to determine the actual temporal resolution.  Such a characterisation can be done for instance with high energy cosmic rays.  In this project you will work on building, commissioning and characterising a compact timing cosmic ray setup, aiming to achieve a resolution better than 100 picoseconds. The work will take place in the R&D labs at Nikhef using a combination of existing detectors and readout electronics as well as new silicon detectors with internal gain (LGADs), and/or fast Micro Channel Plates (MCPs).
  
Activities in the field of (spectral) CT scans are performed in a collaboration between two institutes (Nikhef and CWI) and two companies (ASI and XRE).
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''Contacts: [mailto:kazu.akiba@nikhef.nl Kazu Akiba] and [mailto:martinb@nikhef.nl Martin van Beuzekom]''
  
Some activities that students can work on:  
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===Neutrinos: Searching for Majorana Neutrinos with KamLAND-Zen===
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The KamLAND-Zen experiment, located in the Kamioka mine in Japan, is a large liquid scintillator experiment with 750kg of ultra-pure Xe-136 to search for neutrinoless double-beta decay (0n2b). The observation of the 0n2b process would be evidence for lepton number violation and the Majorana nature of neutrinos, i.e. that neutrinos are their own anti-particles. Current limits on this extraordinary rare hypothetical decay process are presented as a half-life, with a lower limit of 10^26 years. KamLAND-Zen, the world’s most sensitive 0n2b experiment, is currently taking data and there is an opportunity to work on the data analysis, analyzing data with the possibility of taking part in a ground-breaking discovery. The main focus will be on developing new techniques to filter the spallation backgrounds, i.e.  the production of radioactive isotopes by passing muons. There will be close collaboration with groups in the US (MIT, Berkeley, UW) and Japan (Tohoku Univ).
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''Contact: [mailto:decowski@nikhef.nl Patrick Decowski]''
  
- Medical X-ray imaging (CT and ‘flat’ X-ray images): Detection of iodine contrast agent. Detection of calcifications (hint for a tumour).
+
=== Neutrinos: acoustic detection of ultra-high energy neutrinos===
  
- Material research: Using spectral information to identify materials and recognise compounds.
+
The study of the cosmic neutrinos of energies above 1017 eV, the so-called ultra-high energy neutrinos, provides a unique view on the universe and may provide insight in the origin of the most violent astrophysical sources, such as gamma ray bursts, supernovae or even dark matter. In addition, the observation of high energy neutrinos may provide a unique tool to study interactions at high energies. The energy deposition of these extreme neutrinos in water induce a thermo-acoustic signal, which can be detected using sensitive hydrophones. The expected neutrino flux is however extremely low and the signal that neutrinos induce is small. TNO is presently developing sensitive hydrophone technology based on fiber optics. Optical fibers form a natural way to create a distributed sensing system. Using this technology a large scale neutrino telescope can be built in the deep sea. TNO is aiming for a prototype hydrophone which will form the building block of a future telescope.
  
- Determine how much existing applications can benefit from spectral X-ray imaging and look for potential new applications.  
+
The work will be executed at the Nikhef institute and/or the TNO laboratories in Delft. In this project master students have the opportunity to contribute in the following ways:
  
- Characterise, calibrate, optimise X-ray imaging detector systems.  
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'''Project 1:''' Hardware development on fiber optics hydrophones technology Goal: characterize existing prototype optical fibre hydrophones in an anechoic basin at TNO laboratory. Data collection, calibration, characterization, analysis of consequences for design future acoustic hydrophone neutrino telescopes;
 +
Keywords: Optical fiber technology, signal processing, electronics, lab.
  
''Contact: [mailto:martinfr@nikhef.nl Martin Fransen]''
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'''Project 2:''' Investigation of ultra-high energy neutrinos and their interactions with matter. Goal: Discriminate the neutrino signals from the background noises, in particular clicks from whales and dolphins in the deep sea. Study impact on physics reach for future acoustic hydrophone neutrino telescopes;
 +
Keywords: Monte Carlo simulations, particle physics, neutrino physics, data analysis algorithms.
  
=== Detector R&D: Compton camera ===
+
Further information: Info on ultra-high energy neutrinos can be found at: http://arxiv.org/abs/1102.3591; Info on acoustic detection of neutrinos can be found at: http://arxiv.org/abs/1311.7588
  
In the Nikhef R&D group we develop instrumentation for particle physics but we also investigate how particle physics detectors can be used for different purposes. A successful development is the Medipix chip that can be used in X-ray imaging. For use in large scale medical applications compton scattering limits however the energy resolving possibilities. You will investigate whether it is in principle possible to design a X-ray application that detects the compton scattered electron and the absorbed photon. Your ideas can be tested in practice in the lab where a X-ray scan can be performed.
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''Contact: [mailto:ernst-jan.buis@tno.nl Ernst Jan Buis]'' or ''[mailto:ivo.van.vulpen@nikhef.nl Ivo van Vulpen]''
  
''Contact: [mailto:martinfr@nikhef.nl Martin Fransen]''
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=== Neutrinos: Oscillation analysis with the first data of KM3NeT===
  
=== Detector R&D: Holographic projector ===
+
The neutrino telescope KM3NeT is under construction in the Mediterranean Sea aiming to detect cosmic neutrinos. Its first few strings with sensitive photodetectors have been deployed at both the Italian and the French detector sites. Already these few strings provide for the option to reconstruct in the detector the abundant muons stemming from interactions of cosmic rays with the atmosphere and to identify neutrino interactions. In this project the available data will be used together with simulations to best reconstruct the event topologies and optimally identify and reconstruct the first neutrino interactions in the KM3NeT detector. The data will then be used to measure neutrino oscillation parameters, and prepare for a future neutrino mass ordering determination.
  
A difficulty in generating holograms (based on the interference of light) is the required dense spatial light field sampling. One would need pixels of less than 200 nanometer. With larger pixels artefacts occur due to spatial under sampling. A pixel pitch of 200 nm or less is difficult, if not, impossible, to achieve, especially for larger areas. Another challenge is the massive amount of computing power that would be required to control such a dense pixel matrix.  
+
Programming skills are essential, mostly root and C++ will be used.
 +
''Contact: [mailto:bruijn@nikhef.nl Ronald Bruijn] [mailto:h26@nikhef.nl Paul de Jong]''
  
A new holographic projection method has been developed that reduces under sampling artefacts, regardless of spatial sample density. The trick is to create 'pixels' at random but known positions, resulting in an array of (coherent) light points that lacks (or has strongly surpressed) spatial periodicity. As a result a holographic emitter can be built with a significantly lower sample density and less required computing power. This could bring holography in reach for many applications like display, lithography, 3D printing, metrology, etc...
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===Neutrinos: Searching for New Heavy Neutrinos or Other Exotic Particles in KM3NeT===
  
The big question: How does the performance of the holographic emitter depend on sample density and sample positions?
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In this project we will be searching for a new heavy neutrino, looking at signatures created by atmospheric neutrinos interacting in the detector volume of KM3NeT-ORCA. The aim of this project is to study a specific event topology which appears as double blobs of signals detected separately by densely instrumented ORCA detector units. We will be exploiting the tau reconstruction algorithms to verify the possibility of ORCA to detect such signals and to estimate the potential sensitivity of the experiment as well. The data also opens up the possibility to search for other exotic new particles, such as magnetic monopoles. Basic knowledge of elementary particle physics and data analysis techniques will be advantageous. The knowledge of programming languages e.g. python (and possibly C++) and ROOT are advantageous but not mandatory.
  
For this project we are building a proof of concept holographic projector. This set-up will be used to verify simulation results (and also to project some cool holograms of course).
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''Contact: [mailto:suzanbp@nikhef.nl Suzan B. du Pree] [mailto:dveijk@nikhef.nl Daan van Eijk] [mailto:h26@nikhef.nl Paul de Jong]''
  
The aspects of a holographic image we are investigating are:
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===Neutrinos: Dark Matter with KM3NeT-ORCA===
 
- Noise
 
  
- Contrast
+
Dark Matter is thought to be everywhere (we should be swimming through it), but we have no idea what it is. Using the good energy and angular resolutions of the KM3NeT neutrino telescope, we can search for Dark Matter signatures that originate from the center of our galaxy. In this project, we will search for such signatures using the reconstructed track and shower events with the KM3NeT-ORCA detector to discover relatively light Dark Matter particles. Since this year, the KM3NeT-ORCA  experiment has 6 detection lines under the Mediterranean Sea: fully operational and continuously taking data. Using the available data, it is possible to compare data and simulation for different event topologies and to estimate the experiment's sensitivity. The project is suitable for a student who is interested to explore new physics scenarios and willing to develop new skills. Basic knowledge of elementary particle physics and data analysis techniques will be advantageous. The knowledge of programming languages e.g. python (possibly C++) and ROOT data analysis tool are advantageous but not mandatory.
  
- Suppression of under sampling artefacts
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''Contact: [mailto:suzanbp@nikhef.nl Suzan B. du Pree] [mailto:dveijk@nikhef.nl Daan van Eijk]''
  
- Resolution
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===Neutrinos: the Deep Underground Neutrino Experiment (DUNE)===
 
This project offers a very broad field in which you can be active, for that reason a supervisor with the matching expertise must be found based on what you would like to do within this project. If you are interested in this topic, please contact me in an early stage of your orientation such that we can arrange for a proper supervision.
 
  
''Contact: [mailto:martinfr@nikhef.nl Martin Fransen]
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The Deep Underground Neutrino Experiment (DUNE) is under construction in the USA, and will consist of a powerful neutrino beam originating at Fermilab, a near detector at Fermilab, and a far detector in the SURF facility in Lead, South Dakota, 1300 km away. During travelling, neutrinos oscillate and a fraction of the neutrino beam changes flavour; DUNE will determine the neutrino oscillation parameters to unrivaled precision, and try and make a first detection of CP-violation in neutrinos. In this project, various elements of DUNE can be studied, including the neutrino oscillation fit, neutrino physics with the near detector, event reconstruction and classification (including machine learning), or elements of data selection and triggering.
  
=== Detector R&D: Laser Interferometer Space Antenna (LISA) ===
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''Contact: [mailto:h26@nikhef.nl Paul de Jong]''
  
The space-based gravitational wave antenna LISA is without doubt one of the most challenging space missions ever proposed. ESA plans to launch around 2030 three spacecrafts that are separated by a few million kilometers to measure tiny variations in the distances between test-masses located in each spacecraft to detect the gravitational waves from sources such as supermassive black holes. The triangular constellation of the LISA mission is dynamic requiring a constant fine tuning related to the pointing of the laser links between the spacecrafts and a simultaneous refocusing of the telescope. The noise sources related to the laser links are expected to provide a dominant contribution to the LISA performance.
 
  
An update and extension of the LISA science simulation software is needed to assess the hardware development for LISA at Nikhef, TNO and SRON. A position is therefore available for a master student to study the impact of instrumental noise on the performance of LISA. Realistic simulations based on hardware (noise) characterization measurements that were done at TNO will be carried out and compared to the expected tantalizing gravitational wave sources.
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===Gravitational Waves: Computer modelling to design the laser interferometers for the Einstein telescope===
  
Key words: LISA, space, gravitational waves, simulations, signal processing
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A new field of instrument science led to the successful detection of gravitational waves by the LIGO detectors in 2015. We are now preparing the next generation of gravitational wave observatories, such as the Einstein Telescope, with the aim to increase the detector sensitivity by a factor of ten, which would allow, for example, to detect stellar-mass black holes from early in the universe when the first stars began to form. This ambitious goal requires us to find ways to significantly improve the best laser interferometers in the world.
  
''Contact: [mailto:nielsvb@nikhef.nl Niels van Bakel],[mailto:ernst-jan.buis@tno.nl  Ernst-Jan Buis]''
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Gravitational wave detectors, such as LIGO and VIRGO, are complex Michelson-type interferometers enhanced with optical cavities. We develop and use numerical models to study these laser interferometers, to invent new optical techniques and to quantify their performance. For example, we synthesize virtual mirror surfaces to study the effects of higher-order optical modes in the interferometers, and we use opto-mechanical models to test schemes for suppressing quantum fluctuations of the light field. We can offer several projects based on numerical modelling of laser interferometers. All projects will be directly linked to the ongoing design of the Einstein Telescope.
  
=== KM3NeT : Reconstruction of first neutrino interactions in KM3NeT ===
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''Contact: [mailto:a.freise@nikhef.nl Andreas Freise]''
  
The neutrino telescope KM3NeT is under construction in the Mediterranean Sea aiming to detect cosmic neutrinos. Its first two strings with sensitive photodetectors have been deployed 2015&2016. Already these few strings provide for the option to reconstruct in the detector the abundant muons stemming from interactions of cosmic rays with the atmosphere and to identify neutrino interactions. In order to identify neutrinos an accurate reconstruction and optimal understanding of the backgrounds are crucial. In this project we will use the available data to identify and reconstruct the first neutrino interactions in the KM3NeT detector and with this pave the path towards neutrino astronomy.
 
  
Programming skills are essential, mostly root and C++ will be used.
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===Gravitational Waves: Digging away the noise to find the signal===
  
'' Contact: [mailto:bruijn@nikhef.nl Ronald Bruijn]''
+
Gravitational Wave interferometers are extremely sensitive, but suffer
 +
from instrumental issues that produce noise that mimics astrophysical
 +
signals. This needs to be solved as much as possible before the data
 +
analysis. The problem is that  instrumentalists don't know about
 +
analysis pipelines, and data analysts don't know about experimental
 +
details. We need your help to bridge the gap. This is a good opportunity
 +
to learn about both sides and contribute directly to a booming
 +
international field. We have several tools and new ideas for correlating
 +
noises with the state of the instrument. These need to be developed
 +
further, used on years of data, and written up. Will require Python,
 +
signal processing and statistics.
  
=== ANTARES: Analysis of IceCube neutrino sources. ===
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''Contact: [mailto:swinkels@nikhef.nl Bas Swinkels] and [mailto:physarah@gmail.com Sarah Caudill]''
  
The only evidence for high energetic neutrinos from cosmic sources so far comes from detections with the IceCube detector. Most of the detected events were reconstructed with a large uncertainty on their direction, which has prevented an association to astrophysical sources. Only for the high energetic muon neutrino candidates a high resolution in the direction has been achieved, but also for those no significant correlation to astrophysical sources has to date been detected.
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===Theory: The electroweak phase transition and baryogenesis/gravitational wave production===
The ANTARES neutrino telescope has since 2007 continuously taken neutrino data with high angular resolution, which can be exploited to further scrutinize the locations of these neutrino sources. In this project we will address the neutrino sources in a stacked analysis to further probe the origin of the neutrinos with enhanced sensitivity.
 
  
Programming skills are essential, mainly C++ and root will be used.  
+
In extensions of the Standard Model the electroweak phase transition can be first order and proceed via the nucleation of bubbles. Colliding bubbles can produce gravitational waves [1] and plasma particles interacting with the bubbles can generate a matter-antimatter asymmetry [2]. A detailed understanding of the dynamics of the phase transitions is needed to accurately describe these processes.  One project is to study QFT at finite temperature and compare/apply methods that address the non-perturbative IR dynamics of the thermal processes [3,4].  Another project is to calculate the velocity by which the bubbles expand, which is an important parameter for gravitational waves production and baryogensis. A final option is to study the phase transition in conformal Higgs models, which naturally have a strong 1st order phase transition [5].
  
'' Contact: [mailto:dosamt@nikhef.nl Dorothea Samtleben]''
+
[1]https://arxiv.org/abs/1705.01783
 +
[2]https://arxiv.org/pdf/hep-ph/0609145.pdf
 +
[3]https://arxiv.org/pdf/1609.06230.pdf
 +
[4]https://arxiv.org/pdf/1612.00466.pdf
 +
[5]https://arxiv.org/abs/1910.13460.pdf
  
=== VU LaserLaB: Measuring the electric dipole moment (EDM) of the electron ===
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''Contact: [mailto:mpostma@nikhef.nl Marieke Postma]''
  
In collaboration with Nikhef and the Van Swinderen Institute for Particle Physics and Gravity at the University of Groningen, we have recently started an exciting project to measure the electric dipole moment (EDM) of the electron in cold beams of barium-fluoride molecules. The eEDM, which is predicted by the Standard Model of particle physics to be extremely small, is a powerful probe to explore physics beyond this Standard Model. All extensions to the Standard Model, most prominently supersymmetry, naturally predict an electron EDM that is just below the current experimental limits. We aim to improve on the best current measurement by at least an order of magnitude. To do so we will perform a precision measurement on a slow beam of laser-cooled BaF molecules. With this low-energy precision experiment, we test physics at energies comparable to those of LHC!
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===Theory: Higgs inflation===
  
At LaserLaB VU, we are responsible for building and testing a cryogenic source of BaF molecules. The main parts of this source are currently being constructed in the workshop. We are looking for enthusiastic master students to help setup the laser system that will be used to detect BaF. Furthermore, projects are available to perform simulations of trajectory simulations to design a lens system that guides the BaF molecules from the exit of the cryogenic source to the experiment.
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The Higgs boson can drive cosmic inflation provided it has new couplings to gravity [1]. Although classically the model is in excellent agreement with the data, in the full quantum theory there are theoretical consistency issues. One possible project would be to embed Higgs inflation in [2] -- motivated to solve the Strong CP problem and explain the matter-antimatter asymmetry -- as the extended Higgs sector can alleviate the theoretical constraints. Another direction is to consider multiple new couplings to gravity [3], to see whether the ensuing inflationary dynamics allows for the production of primordial black holes.  
  
'' Contact: [mailto:H.L.Bethlem@vu.nl Rick Bethlem]''
+
[1]https://arxiv.org/pdf/1307.0708.pdf
 +
[2]https://arxiv.org/pdf/2007.12711.pdf
 +
[3]https://arxiv.org/abs/2011.09485.pdf
  
 +
''Contact: [mailto:mpostma@nikhef.nl Marieke Postma]''
  
=== VU LaserLab: Physics beyond the Standard model from molecules ===
+
===Theory: Neutrinos, hierarchy problem and cosmology===
  
Our team, with a number of staff members (Ubachs, Eikema, Salumbides, Bethlem, Koelemeij) focuses on precision measurements in the hydrogen molecule, and its isotopomers. The work aims at testing the QED calculations of energy levels in H2, D2, T2, HD, etc. with the most precise measurements, where all kind of experimental laser techniques play a role (cw and pulsed lasers, atomic clocks, frequency combs, molecular beams). Also a target of studies is the connection to the "Proton size puzzle", which may be solved  through studies in the hydrogen molecular isotopes.
+
The electroweak hierachy is radiatively stable if the quadratic term in the Higgs potential is generated dynamically. This is achieved in 'the neutrino option' [1] where the Higgs potential stems exclusively from quantum effects of heavy right-handed neutrinos, which can also generate the mass pattern of the oberved left-handed neutrinos.  The project focusses on model building aspects (e.g. [2]) and the cosmology (e.g. leptogenesis [3]) of these set-ups.
  
In the past half year we have produced a number of important results that are described in
+
[1] https://arxiv.org/pdf/1703.10924.pdf
the following papers:
+
[2] https://arxiv.org/pdf/1807.11490.pdf
* Frequency comb (Ramsey type) electronic  excitations in the  H2 molecule:
+
[3] https://arxiv.org/pdf/1905.12642.pdf
see: Deep-ultraviolet frequency metrology of H2 for tests of molecular quantum theory
 
http://www.nat.vu.nl/~wimu/Publications/Altmann-PRL-2018.pdf
 
* ''Precision measurement of an infrared transition in the HD molecule''
 
see: Sub-Doppler frequency metrology in HD for tests of fundamental physics: https://arxiv.org/abs/1712.08438
 
* ''The first precision study in molecular tritium T2''
 
see: Relativistic and QED effects in the fundamental vibration of T2:  http://arxiv.org/abs/1803.03161
 
* ''Dissociation energy of the hydrogen molecule at 10^-9 accuracy'' paper submitted to Phys. Rev. Lett.
 
* ''Probing QED and fundamental constants through laser spectroscopy of vibrational transitions in HD+''
 
This is also a study of the hydrogen molecular ion HD+, where important results were  obtained not so long ago, and where we have a strong activity: http://www.nat.vu.nl/~wimu/Publications/ncomms10385.pdf
 
  
These five results mark the various directions we are pursuing, and in all directions we aim at obtaining improvements. Specific projects with students can be defined; those are mostly experimental, although there might be some theoretical tasks, like:
+
''Contact: [mailto:mpostma@nikhef.nl Marieke Postma]''
* Performing calculations of hyperfine structures
 
  
As for the theory there might also be an international connection for specifically bright theory students: we collaborate closely with prof. Krzystof Pachucki; we might find an opportunity
 
for a student to perform (the best !) QED calculations in molecules, when working in Warsaw and partly in Amsterdam. Prof Frederic Merkt from the ETH Zurich, an expert in the field, will come to work with us on "hydrogen"
 
during August - Dec 2018 while on sabbatical.
 
  
'' Contact: [mailto:w.m.g.ubachs@vu.nl Wim Ubachs] [mailto:k.s.e.eikema@vu.nl Kjeld Eikema] [mailto:h.l.bethlem@vu.nl Rick Bethlem]''
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----
  
  

Latest revision as of 12:32, 13 September 2021

Master Thesis Research Projects

The following Master thesis research projects are offered at Nikhef. If you are interested in one of these projects, please contact the coordinator listed with the project.

Projects with a 2021 start

ALICE: The next-generation multi-purpose detector at the LHC

This main goal of this project is to focus on the next-generation multi-purpose detector planned to be built at the LHC. Its core will be a nearly massless barrel detector consisting of truly cylindrical layers based on curved wafer-scale ultra-thin silicon sensors with MAPS technology, featuring an unprecedented low material budget of 0.05% X0 per layer, with the innermost layers possibly positioned inside the beam pipe. The proposed detector is conceived for studies of pp, pA and AA collisions at luminosities a factor of 20 to 50 times higher than possible with the upgraded ALICE detector, enabling a rich physics program ranging from measurements with electromagnetic probes at ultra-low transverse momenta to precision physics in the charm and beauty sector.

Contact: Panos Christakoglou and Alessandro Grelli and Marco van Leeuwen

ALICE: Searching for the strongest magnetic field in nature

In case of a non-central collision between two Pb ions, with a large value of impact parameter (b), the charged nucleons that do not participate in the interaction (called spectators) create strong magnetic fields. A back of the envelope calculation using the Biot-Savart law brings the magnitude of this filed close to 10^19Gauss in agreement with state of the art theoretical calculation, making it the strongest magnetic field in nature. The presence of this field could have direct implications in the motion of final state particles. The magnetic field, however, decays rapidly. The decay rate depends on the electric conductivity of the medium which is experimentally poorly constrained. Overall, the presence of the magnetic field, the main goal of this project, is so far not confirmed experimentally.

Contact: Panos Christakoglou

ALICE: Looking for parity violating effects in strong interactions

Within the Standard Model, symmetries, such as the combination of charge conjugation (C) and parity (P), known as CP-symmetry, are considered to be key principles of particle physics. The violation of the CP-invariance can be accommodated within the Standard Model in the weak and the strong interactions, however it has only been confirmed experimentally in the former. Theory predicts that in heavy-ion collisions, in the presence of a deconfined state, gluonic fields create domains where the parity symmetry is locally violated. This manifests itself in a charge-dependent asymmetry in the production of particles relative to the reaction plane, what is called the Chiral Magnetic Effect (CME). The first experimental results from STAR (RHIC) and ALICE (LHC) are consistent with the expectations from the CME, however further studies are needed to constrain background effects. These highly anticipated results have the potential to reveal exiting, new physics.

Contact: Panos Christakoglou

ALICE: Machine learning techniques as a tool to study the production of heavy flavour particles

There was recently a shift in the field of heavy-ion physics triggered by experimental results obtained in collisions between small systems (e.g. protons on protons). These results resemble the ones obtained in collisions between heavy ions. This consequently raises the question of whether we create the smallest QGP droplet in collisions between small systems. The main objective of this project will be to study the production of charm particles such as D-mesons and Λc-baryons in pp collisions at the LHC. This will be done with the help of a new and innovative technique which is based on machine learning (ML). The student will also extend the studies to investigate how this production rate depends on the event activity e.g. on how many particles are created after every collision.

Contact: Panos Christakoglou and Alessandro Grelli

ALICE: Energy Loss of Energetic Quarks and Gluons in the Quark-Gluon Plasma

One of the ways to study the quark-gluon plasma that is formed in high-energy nuclear collisions, is using high-energy partons (quarks or gluons) that are produced early in the collision and interact with the quark-gluon plasma as they propagate through it. There are several current open questions related to this topic, which can be explored in a Master's project. For example, we would like to use the new Monte Carlo generator framework JetScape to simulate collisions to see whether we can extract information about the interaction with the quark-gluon plasma. In the project you will collaborate with one of the PhD students or postdocs in our group to use the model to generate predictions of measurements and compare those to data analysis results. Depending on your interests, the project can focus more on the modeling aspects or on the analysis of experimental data from the ALICE detector at the LHC.

Contact: Marco van Leeuwen and Marta Verweij

ALICE: Extreme Rare Probes of the Quark-Gluon Plasma

The quark-gluon plasma is formed in high-energy nuclear collisions and also existed shortly after the big bang. With the large amount of data collected in recent years at the Large Hadron Collider at CERN, rare processes that previously were not accessible provide now new ways to study how the quark-gluon plasma emerges from the fundamental theory of strong interaction. One of such processes is the heavy W boson which in many cases decays to two quarks. The W boson itself doesn’t interact with the quark-gluon plasma because it doesn’t carry color, but the quark decay products do interact with the plasma and therefore provide an ideal tool to study the space-time evolution of this hot and dense medium. In this project you will use data from the ALICE detector at the LHC and simulated data from generators to study various physics mechanisms that could be happening in the real collisions.

Contact: Marta Verweij and Marco van Leeuwen

ALICE: Jet Quenching with Machine Learning

Machine learning applications are rising steadily as a vital tool in the field of data science but are relatively new in the particle physics community. In this project machine learning tools will be used to gain insights into the modification of a parton shower in the quark-gluon plasma (QGP). The QGP is created in high-energy nuclear collisions and only lives for a very short period of time. Highly energetic partons created in the same collisions interact with the plasma while they travers it and are observed as a collimated spray of particles, known as jets, in the detector. One of the key recent insights is that the internal structure of jets provides information about the evolution of the QGP. With data recorded by the ALICE experiment, you will use jet substructure techniques in combination with machine learning algorithms to dissect the structure of the QGP. Machine learning will be used to select the regions of radiation phase space that are affected by the presence of the QGP.

Contact: Marta Verweij and Marco van Leeuwen


ATLAS: Top Spin and EFTs in the Wtb vertex

The top quark has an exceptional high mass, close to the electroweak symmetry breaking scale and therefore sensitive to new physics effects. Theoretically, new physics is well described in the EFT framework [1]. The (EFT) operators are experimentally well accessible in single top t-channel production where the top quark is produced spin polarized. The focus at Nikhef is the operator O_{tW} with a possible imaginary phase, leading to CP violation. Experimentally, many angular distribution are reconstructed in the top rest frame to hunt for these effects. There are several challenging analysis-topics for master students, which can also be tailored a bit your interests: 1) MC study EFT effects from background substraction. 2) NLO reweighting (as function of EFT parameters) based on Madgraph 3) Kinematic Fitter neural network estimation vs analytic as available 4) Pt dependent analysis of existing analysis 5) Make a combination with a higgs channel? (difficult) 6) Make a combination with other top channels? (difficult)

More info in this presentation: www.nikhef.nl/~h73/top_masterstudenten_mrt2021.pptx and/or in the video: https://video.uva.nl/media/t/0_0f2fuazf


[1] https://arxiv.org/abs/1807.03576

Contact: Marcel Vreeswijk [1] and Jordy Degens [2]

ATLAS: The Next Generation

After the observation of the coupling of Higgs bosons to fermions of the third generation, the search for the coupling to fermions of the second generation is one of the next priorities for research at CERN's Large Hadron Collider. The search for the decay of the Higgs boson to two charm quarks is very new [1] and we see various opportunities for interesting developments. For this project we propose improvements in reconstruction (using exclusive decays), advanced analysis techiques (using deep learning methods) and expanding the theory interpretation. Another opportunity would be the development of the first statistical combination of results between the ATLAS and CMS experiment, which could significantly improve the discovery potentional.

[1] https://arxiv.org/abs/1802.04329

Contact: Tristan du Pree

ATLAS: The Most Energetic Higgs Boson

The production of Higgs bosons at the highest energies could give the first indications for deviations from the standard model of particle physics, but production energies above 500 GeV have not been observed yet [1]. The LHC Run-2 dataset, collected during the last 4 years, might be the first opportunity to observe such processes, and we have various ideas for new studies. Possible developments include the improvement of boosted reconstruction techniques, for example using multivariate deep learning methods. Also, there are various opportunities for unexplored theory interpretations (using the MadGraph event generator), including effective field theory models (with novel ‘morphing’ techniques) and new interpretations of the newly observed boosted VZ(bb) process.

[1] https://arxiv.org/abs/1709.05543

Contact: Tristan du Pree

ATLAS: Searching for new particles in very energetic diboson production

The discovery of new phenomena in high-energy proton–proton collisions is one of the main goals of the Large Hadron Collider (LHC). New heavy particles decaying into a pair of vector bosons (WW, WZ, ZZ) are predicted in several extensions to the Standard Model (e.g. extended gauge-symmetry models, Grand Unified theories, theories with warped extra dimensions, etc). In this project we will investigate new ideas to look for these resonances in a region that is yet unexplored in the data. We will focus on the final states where both vector bosons decay into quarks as they are expected to bring the highest sensitivity [1]. We will try to reconstruct and exploit the polarisation of the vector bosons (using machine learning methods) and then tackle the problem of estimating contributions from beyond the Standard Model processes in the tails of the mass distribution.

[1] https://arxiv.org/abs/1906.08589

Contact: Flavia de Almeida Dias

ATLAS R&D: Study of LGAD sensors

The Atlas detector has been installed more than a decade ago. Several upgrades of the detector are being worked on that will adapt the ATLAS experiment to the so-called High Luminosity LHC. A new (sub)detector that will be installed and become part of the Atlas detector is the High-Granularity Timing Detector (HGTD) detector. The HGTD will measure very precisely the passage time of particles in the detector and will help identify from which of the plurious proton-proton collisions the particle originates from. The HGTD is partly made of LGAD sensors. These are granulated silicon sensors dedicatedly designed for the HGTD. In this project we will characterise the LGAD sensors.

Contact: Hella Snoek

LHCb: Measuring differences between electrons and muons, beyond the Standard Model

A current “hot topic” in the field of particle physics is the potential violation of lepton-universality. At the LHCb experiment, lepton-universality tests are performed by looking at the ratio of decays into muons and into electrons/taus. Recent measurements in meson modes show hints (2 ? 3?) of lepton non-universality. Baryonic modes, however, have been less studied and provide an independent test of lepton-universality. At Nikhef, we study the decay Lambdab->Lambda l+l- , where l can be an electron or a muon. There are two possible project topics:

1. Identifying novel analysis techniques in the high di-lepton invariant mass region. Electrons in this region undergo more Bremsstrahlung, and therefore have a worse momentum resolution, meaning background from the resonant Psi(2S) mode can leak into our signal. Since we expect most of our signal in this region, it is important to improve this, most likely using machine learning techniques.

2. Identifying, simulating, and setting up a rejection for partially reconstructed Lambdab->Lambda* l+l- backgrounds. By not fully reconstructing the excited Lambda*0, we can mis-reconstruct it as a signal candidate. Machine learning techniques could be explored.

Contact: Lex Greeven and Niels Tuning

LHCb: New physics in the angular distributions of B decays to K*ee

Lepton flavour violation in B decays can be explained by a variety of non-standard model interactions. Angular distributions in decays of a B meson to a hadron and two leptons are an important source of information to understand which model is correct. Previous analyses at the LHCb experiment have considered final states with a pair of muons. Our LHCb group at Nikhef concentrates on a new measurement of angular distributions in decays with two electrons. The main challenge in this measurement is the calibration of the detection efficiency. In this project you will confront estimates of the detection efficiency derived from simulation with decay distributions in a well known B decay. Once the calibration is understood, the very first analysis of the angular distributions in the electron final state can be performed.

Contact: Wouter Hulsbergen and Mara Soares

LHCb: Discovering heavy neutrinos in B decays

Neutrinos are the lightest of all fermions in the standard model. Mechanisms to explain their small mass rely on the introduction of new, much heavier, neutral leptons. If the mass of these new neutrinos is below the b-quark mass, they can be observed in B hadron decays.

In this project we search for the decay of B+ mesons in into an ordinary electron or muon and the yet undisovered heavy neutrino. The heavy neutrino is expected to be unstable and in turn decay quickly into a charged pion and another electron or muon. The final state in which the two leptons differ in flavour, "B+ to e mu pi", is particularly interesting: It is forbidden in the standard model, such that backgrounds are small. The analysis will be performed within the LHCb group at Nikhef using LHCb run-2 data.


Contact: Lera Lukashenko and Wouter Hulsbergen

LHCb: Searching for dark matter in exotic six-quark particles

3/4 of the mass in the Universe is of unknown type. Many hypotheses about this dark matter have been proposed, but none confirmed. Recently it has been proposed that it could be made of particles made of the six quarks uuddss. Such a particle could be produced in decays of heavy baryons. It is proposed to use Xi_b baryons produced at LHCb to search for such a state. The latter would appear as missing 4-momentum in a kinematically constrained decay. The project consists in optimising a selection and applying it to LHCb data. See arXiv:1708.08951

Contact: Patrick Koppenburg

With the Dark Matter group: Fine structure constant

The fine-structure constant has been measured by many experiments in the past and it is one of the most precisely known constants in nature. The goal of this project is to design and build an experiment to do an in-house measurement of the fine structure constant by investigating positron annihilation to two and to three photons. The work within this project encompasses the full breadth of experimental physics: from a conceptual design to the final analysis of the data. In addition, there is a budget of 10kEuro available to purchase the necessary hardware for the project. Supervision will be done by Colijn and the Nikhef director Bentvelsen.

Contact: Auke-Pieter Colijn

Dark Matter: Sensitive tests of wavelength-shifting properties of materials for dark matter detectors

Rare event search experiments that look for neutrino and dark matter interactions are performed with highly sensitive detector systems, often relying on scintillators, especially liquid noble gases, to detect particle interactions. Detectors consist of structural materials that are assumed to be optically passive, and light detection systems that use reflectors, light detectors, and sometimes, wavelength-shifting materials. MSc theses are available related to measuring the efficiency of light detection systems that might be used in future detectors. Furthermore, measurements to ensure that presumably passive materials do not fluoresce, at the low level relevant to the detectors, can be done. Part of the thesis work can include Monte Carlo simulations and data analysis for current and upcoming dark matter detectors, to study the effect of different levels of desired and nuisance wavelength shifting. In this project, students will acquire skills in photon detection, wavelength shifting technologies, vacuum systems, UV and extreme-UV optics, detector design, and optionally in C++ programming, data analysis, and Monte Carlo techniques.

Contact: Tina Pollmann and Patrick Decowski

Dark Matter: Building better Dark Matter Detectors - the XAMS R&D Setup

The Amsterdam Dark Matter group operates an R&D xenon detector at Nikhef. The detector is a dual-phase xenon time-projection chamber and contains about 4kg of ultra-pure liquid xenon. We use this detector for the development of new detection techniques - such as utilizing our newly installed silicon photomultipliers - and to improve the understanding of the response of liquid xenon to various forms of radiation. The results could be directly used in the XENONnT experiment, the world’s most sensitive direct detection dark matter experiment at the Gran Sasso underground laboratory, or for future Dark Matter experiments like DARWIN. We have several interesting projects for this facility. We are looking for someone who is interested in working in a laboratory on high-tech equipment, modifying the detector, taking data and analyzing the data him/herself. You will "own" this experiment.

Contact: Patrick Decowski and Auke Colijn

Dark Matter: Searching for Dark Matter Particles - XENONnT Data Analysis

The XENON collaboration has used the XENON1T detector to achieve the world’s most sensitive direct detection dark matter results and is currently starting the XENONnT successor experiment. The detectors operate at the Gran Sasso underground laboratory and consist of so-called dual-phase xenon time-projection chambers filled with ultra-pure xenon. Our group has an opening for a motivated MSc student to do analysis with the new data coming from the XENONnT detector. The work will consist of understanding the detector signals and applying a deep neural network to improve the (gas-) background discrimination in our Python-based analysis tool to improve the sensitivity for low-mass dark matter particles. The work will continue a study started by a recent graduate. There will also be opportunity to do data-taking shifts at the Gran Sasso underground laboratory in Italy.

Contact: Patrick Decowski and Auke Colijn

Dark Matter: The Ultimate Dark Matter Experiment - DARWIN Sensitivity Studies

DARWIN is the “ultimate” direct detection dark matter experiment, with the goal to reach the so-called “neutrino floor”, when neutrinos become a hard-to-reduce background. The large and exquisitely clean xenon mass will allow DARWIN to also be sensitive to other physics signals such as solar neutrinos, double-beta decay from Xe-136, axions and axion-like particles etc. While the experiment will only start in 2027, we are in the midst of optimizing the experiment, which is driven by simulations. We have an opening for a student to work on the GEANT4 Monte Carlo simulations for DARWIN, as part of a simulation team together with the University of Freiburg and Zurich. We are also working on a “fast simulation” that could be included in this framework. It is your opportunity to steer the optimization of a large and unique experiment. This project requires good programming skills (Python and C++) and data analysis/physics interpretation skills. Contact: Patrick Decowski and Auke Colijn

Detector R&D: Test beam with a bent ALPIDE monolithic active pixel sensor

The next ALICE inner tracking system that is to be installed in 2025 at the large hadron collider (LHC) will feature ultrathin silicon monolithic active pixel sensors (MAPS). The current ALICE tracking system that has just been installed already features this new, very thin pixel detectors with low noise and low power consumption, but for the next tracker they will be bent around the beam pipe. In this project, you will be part of the international ALICE collaboration. You will analyze data from beam tests performed at CERN and DESY to characterize bent pixel detectors. You will be part of the Nikhef R&D group and will also have the opportunity to perform your own measurements in the lab on the ALICE pixel detector (ALPIDE) or on an even thinner version thereof. If the travel situation allows, you will have the opportunity to join the ALICE test beam group in Hamburg at DESY to take part in the exciting experience of taking real data. Contact: Jory Sonneveld

Detector R&D: Modeling radiation damage for the next generation ATLAS pixel detector

In 2026 the ATLAS tracker will be upgraded to the largest silicon tracker in the world. This tracker will have to cope with very large data rates foreseen in the upgraded high luminosity large hadron collider (HL-LHC). From then on, this tracker will see very high rates of radiation, particularly in the inner tracker closest to the LHC beam line. In this project you will evaluate the performance of the silicon pixel sensors for the new ATLAS inner tracker. You will learn to use commercial technology computer aided design software (TCAD) for modeling semiconductors widely used in the semiconductor industry and compare your simulation results with data from the beam tests performed on the new modules for ATLAS ITk at CERN. You will also use and develop fast simulation tools like Allpix Squared for which you will use your C++ programming skills. As a member of the international ATLAS collaboration you will present your work in an international environment, and you will be part of the Nikhef detector R&D group where you will learn about the newest fast timing silicon detector technologies for LHC experiments and beyond. Contact: Jory Sonneveld

Detector R&D: Characterisation of Trench Isolated Low Gain Avalanche Detectors (TI-LGAD)

The future vertex detector of the LHCb Experiment needs to measure the spatial coordinates and time of the particles originating in the LHC proton-proton collisions with resolutions better than 10 um and 50 ps, respectively. Several technologies are being considered to achieve these resolutions. Among those is a novel sensor technology called Trench Isolated Low Gain Avalanche Detector. Prototype pixelated sensors have been manufactured recently and have to be characterised. Therefore these new sensors will be bump bonded to a Timepix4 ASIC which provides charge and time measurements in each of 230 thousand pixels. Characterisation will be done using a lab setup at Nikhef, and includes tests with a micro-focused laser beam, radioactive sources, and possibly with particle tracks obtained in a test-beam. This project involves data taking with these new devices and analysing the data to determine the performance parameters such as the spatial and temporal resolution. as function of temperature and other operational conditions.

Contacts: Kazu Akiba and Martin van Beuzekom

Detector R&D: Studying fast timing detectors

Fast timing detectors are the solution for future tracking detectors. In future LHC operation conditions and future colliders, more and more particles are produced per collision. The high particle densities make it increasingly more difficult to separate particle trajectories with the spatial information that current silicon tracking detectors provide. A solution would be to add very precise (in order of 10ps) timestamps to the spatial measurements of the particle trackers. A good understanding of the performance of fast timing detectors is necessary. With the user of a pulsed laser in the lab we study the characteristics of several prototype detectors.

Contact: Hella Snoek or Kazu Akiba

Detector R&D: Laser Interferometer Space Antenna (LISA) - Wavefront sensors for gravitational wave detection

The space-based gravitational wave antenna LISA is one of the most challenging space missions ever proposed. ESA plans to launch around 2030 three spacecraft separated by a few million kilometres. This constellation measures tiny variations in the distances between test-masses located in each satellite to detect gravitational waves from sources such as supermassive black holes. LISA is based on laser interferometry, and the three satellites form a giant Michelson interferometer. LISA measures a relative phase shift between one local laser and one distant laser by light interference. The phase shift measurement requires sensitive wavefront sensors. The Nikhef DR&D group fabricated prototype sensors in 2020 together with the Photonics industry and the Dutch institute for space research SRON. As an MSc student, you will work on various aspects of the wavefront sensor development: study the performance of the epitaxial stacks of Indium-Gallium-Arsenide, setting up test benches to characterize the sensors, and performing the actual tests and data analysis.

Contact: Niels van Bakel

Detector R&D: Time tracking Cosmic rays

One of the main challenges in particle physics detector technologies is to perform precise time measurements while maintaining, or even improving, the excellent spatial resolution. New sensor prototypes need to be characterised using charged particles in order to determine the actual temporal resolution. Such a characterisation can be done for instance with high energy cosmic rays. In this project you will work on building, commissioning and characterising a compact timing cosmic ray setup, aiming to achieve a resolution better than 100 picoseconds. The work will take place in the R&D labs at Nikhef using a combination of existing detectors and readout electronics as well as new silicon detectors with internal gain (LGADs), and/or fast Micro Channel Plates (MCPs).

Contacts: Kazu Akiba and Martin van Beuzekom

Neutrinos: Searching for Majorana Neutrinos with KamLAND-Zen

The KamLAND-Zen experiment, located in the Kamioka mine in Japan, is a large liquid scintillator experiment with 750kg of ultra-pure Xe-136 to search for neutrinoless double-beta decay (0n2b). The observation of the 0n2b process would be evidence for lepton number violation and the Majorana nature of neutrinos, i.e. that neutrinos are their own anti-particles. Current limits on this extraordinary rare hypothetical decay process are presented as a half-life, with a lower limit of 10^26 years. KamLAND-Zen, the world’s most sensitive 0n2b experiment, is currently taking data and there is an opportunity to work on the data analysis, analyzing data with the possibility of taking part in a ground-breaking discovery. The main focus will be on developing new techniques to filter the spallation backgrounds, i.e. the production of radioactive isotopes by passing muons. There will be close collaboration with groups in the US (MIT, Berkeley, UW) and Japan (Tohoku Univ). Contact: Patrick Decowski

Neutrinos: acoustic detection of ultra-high energy neutrinos

The study of the cosmic neutrinos of energies above 1017 eV, the so-called ultra-high energy neutrinos, provides a unique view on the universe and may provide insight in the origin of the most violent astrophysical sources, such as gamma ray bursts, supernovae or even dark matter. In addition, the observation of high energy neutrinos may provide a unique tool to study interactions at high energies. The energy deposition of these extreme neutrinos in water induce a thermo-acoustic signal, which can be detected using sensitive hydrophones. The expected neutrino flux is however extremely low and the signal that neutrinos induce is small. TNO is presently developing sensitive hydrophone technology based on fiber optics. Optical fibers form a natural way to create a distributed sensing system. Using this technology a large scale neutrino telescope can be built in the deep sea. TNO is aiming for a prototype hydrophone which will form the building block of a future telescope.

The work will be executed at the Nikhef institute and/or the TNO laboratories in Delft. In this project master students have the opportunity to contribute in the following ways:

Project 1: Hardware development on fiber optics hydrophones technology Goal: characterize existing prototype optical fibre hydrophones in an anechoic basin at TNO laboratory. Data collection, calibration, characterization, analysis of consequences for design future acoustic hydrophone neutrino telescopes; Keywords: Optical fiber technology, signal processing, electronics, lab.

Project 2: Investigation of ultra-high energy neutrinos and their interactions with matter. Goal: Discriminate the neutrino signals from the background noises, in particular clicks from whales and dolphins in the deep sea. Study impact on physics reach for future acoustic hydrophone neutrino telescopes; Keywords: Monte Carlo simulations, particle physics, neutrino physics, data analysis algorithms.

Further information: Info on ultra-high energy neutrinos can be found at: http://arxiv.org/abs/1102.3591; Info on acoustic detection of neutrinos can be found at: http://arxiv.org/abs/1311.7588

Contact: Ernst Jan Buis or Ivo van Vulpen

Neutrinos: Oscillation analysis with the first data of KM3NeT

The neutrino telescope KM3NeT is under construction in the Mediterranean Sea aiming to detect cosmic neutrinos. Its first few strings with sensitive photodetectors have been deployed at both the Italian and the French detector sites. Already these few strings provide for the option to reconstruct in the detector the abundant muons stemming from interactions of cosmic rays with the atmosphere and to identify neutrino interactions. In this project the available data will be used together with simulations to best reconstruct the event topologies and optimally identify and reconstruct the first neutrino interactions in the KM3NeT detector. The data will then be used to measure neutrino oscillation parameters, and prepare for a future neutrino mass ordering determination.

Programming skills are essential, mostly root and C++ will be used. Contact: Ronald Bruijn Paul de Jong

Neutrinos: Searching for New Heavy Neutrinos or Other Exotic Particles in KM3NeT

In this project we will be searching for a new heavy neutrino, looking at signatures created by atmospheric neutrinos interacting in the detector volume of KM3NeT-ORCA. The aim of this project is to study a specific event topology which appears as double blobs of signals detected separately by densely instrumented ORCA detector units. We will be exploiting the tau reconstruction algorithms to verify the possibility of ORCA to detect such signals and to estimate the potential sensitivity of the experiment as well. The data also opens up the possibility to search for other exotic new particles, such as magnetic monopoles. Basic knowledge of elementary particle physics and data analysis techniques will be advantageous. The knowledge of programming languages e.g. python (and possibly C++) and ROOT are advantageous but not mandatory.

Contact: Suzan B. du Pree Daan van Eijk Paul de Jong

Neutrinos: Dark Matter with KM3NeT-ORCA

Dark Matter is thought to be everywhere (we should be swimming through it), but we have no idea what it is. Using the good energy and angular resolutions of the KM3NeT neutrino telescope, we can search for Dark Matter signatures that originate from the center of our galaxy. In this project, we will search for such signatures using the reconstructed track and shower events with the KM3NeT-ORCA detector to discover relatively light Dark Matter particles. Since this year, the KM3NeT-ORCA experiment has 6 detection lines under the Mediterranean Sea: fully operational and continuously taking data. Using the available data, it is possible to compare data and simulation for different event topologies and to estimate the experiment's sensitivity. The project is suitable for a student who is interested to explore new physics scenarios and willing to develop new skills. Basic knowledge of elementary particle physics and data analysis techniques will be advantageous. The knowledge of programming languages e.g. python (possibly C++) and ROOT data analysis tool are advantageous but not mandatory.

Contact: Suzan B. du Pree Daan van Eijk

Neutrinos: the Deep Underground Neutrino Experiment (DUNE)

The Deep Underground Neutrino Experiment (DUNE) is under construction in the USA, and will consist of a powerful neutrino beam originating at Fermilab, a near detector at Fermilab, and a far detector in the SURF facility in Lead, South Dakota, 1300 km away. During travelling, neutrinos oscillate and a fraction of the neutrino beam changes flavour; DUNE will determine the neutrino oscillation parameters to unrivaled precision, and try and make a first detection of CP-violation in neutrinos. In this project, various elements of DUNE can be studied, including the neutrino oscillation fit, neutrino physics with the near detector, event reconstruction and classification (including machine learning), or elements of data selection and triggering.

Contact: Paul de Jong


Gravitational Waves: Computer modelling to design the laser interferometers for the Einstein telescope

A new field of instrument science led to the successful detection of gravitational waves by the LIGO detectors in 2015. We are now preparing the next generation of gravitational wave observatories, such as the Einstein Telescope, with the aim to increase the detector sensitivity by a factor of ten, which would allow, for example, to detect stellar-mass black holes from early in the universe when the first stars began to form. This ambitious goal requires us to find ways to significantly improve the best laser interferometers in the world.

Gravitational wave detectors, such as LIGO and VIRGO, are complex Michelson-type interferometers enhanced with optical cavities. We develop and use numerical models to study these laser interferometers, to invent new optical techniques and to quantify their performance. For example, we synthesize virtual mirror surfaces to study the effects of higher-order optical modes in the interferometers, and we use opto-mechanical models to test schemes for suppressing quantum fluctuations of the light field. We can offer several projects based on numerical modelling of laser interferometers. All projects will be directly linked to the ongoing design of the Einstein Telescope.

Contact: Andreas Freise


Gravitational Waves: Digging away the noise to find the signal

Gravitational Wave interferometers are extremely sensitive, but suffer from instrumental issues that produce noise that mimics astrophysical signals. This needs to be solved as much as possible before the data analysis. The problem is that instrumentalists don't know about analysis pipelines, and data analysts don't know about experimental details. We need your help to bridge the gap. This is a good opportunity to learn about both sides and contribute directly to a booming international field. We have several tools and new ideas for correlating noises with the state of the instrument. These need to be developed further, used on years of data, and written up. Will require Python, signal processing and statistics.

Contact: Bas Swinkels and Sarah Caudill

Theory: The electroweak phase transition and baryogenesis/gravitational wave production

In extensions of the Standard Model the electroweak phase transition can be first order and proceed via the nucleation of bubbles. Colliding bubbles can produce gravitational waves [1] and plasma particles interacting with the bubbles can generate a matter-antimatter asymmetry [2]. A detailed understanding of the dynamics of the phase transitions is needed to accurately describe these processes. One project is to study QFT at finite temperature and compare/apply methods that address the non-perturbative IR dynamics of the thermal processes [3,4]. Another project is to calculate the velocity by which the bubbles expand, which is an important parameter for gravitational waves production and baryogensis. A final option is to study the phase transition in conformal Higgs models, which naturally have a strong 1st order phase transition [5].

[1]https://arxiv.org/abs/1705.01783 [2]https://arxiv.org/pdf/hep-ph/0609145.pdf [3]https://arxiv.org/pdf/1609.06230.pdf [4]https://arxiv.org/pdf/1612.00466.pdf [5]https://arxiv.org/abs/1910.13460.pdf

Contact: Marieke Postma

Theory: Higgs inflation

The Higgs boson can drive cosmic inflation provided it has new couplings to gravity [1]. Although classically the model is in excellent agreement with the data, in the full quantum theory there are theoretical consistency issues. One possible project would be to embed Higgs inflation in [2] -- motivated to solve the Strong CP problem and explain the matter-antimatter asymmetry -- as the extended Higgs sector can alleviate the theoretical constraints. Another direction is to consider multiple new couplings to gravity [3], to see whether the ensuing inflationary dynamics allows for the production of primordial black holes.

[1]https://arxiv.org/pdf/1307.0708.pdf [2]https://arxiv.org/pdf/2007.12711.pdf [3]https://arxiv.org/abs/2011.09485.pdf

Contact: Marieke Postma

Theory: Neutrinos, hierarchy problem and cosmology

The electroweak hierachy is radiatively stable if the quadratic term in the Higgs potential is generated dynamically. This is achieved in 'the neutrino option' [1] where the Higgs potential stems exclusively from quantum effects of heavy right-handed neutrinos, which can also generate the mass pattern of the oberved left-handed neutrinos. The project focusses on model building aspects (e.g. [2]) and the cosmology (e.g. leptogenesis [3]) of these set-ups.

[1] https://arxiv.org/pdf/1703.10924.pdf [2] https://arxiv.org/pdf/1807.11490.pdf [3] https://arxiv.org/pdf/1905.12642.pdf

Contact: Marieke Postma





Last year's MSc Projects