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.  
  
 +
== Projects with September 2019 start ==
  
−
== New Projects [start in September 2018] ==
+
=== Theory: The Effective Field Theory Pathway to New Physics at the LHC ===
  
 +
A very promising framework to parametrise in a robust and model-independent way deviations from the Standard Model (SM) induced by new heavy particles is the Standard  Model Effective Field Theory (SMEFT). In this formalism, Beyond the SM effects are encapsulated in higher-dimensional operators constructed from SM fields respecting their symmetry properties. In this project, we aim to carry out a global analysis of the SMEFT from high-precision LHC data, including Higgs boson production, flavour observables, and low-energy measurements. This analysis will be carried out in the context of the recently developed SMEFiT approach [1] based on Machine Learning techniques to efficiently explore the complex theory parameter space. The ultimate goal is either to uncover glimpses of new particles or interactions at the LHC, or to derive the most stringent model-independent bounds to date on general theories of New Physics.
  
−
=== The XENON Dark Matter Experiment: Data Analysis ===
+
''Contact: [mailto:j.rojo@vu.nl Juan Rojo]"
  
−
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.  
+
[1] https://arxiv.org/abs/1901.05965
  
−
''Contact: [mailto:decowski@nikhef.nl Patrick Decowski]''
+
=== Theory: Pinning down the initial state of heavy-ion collisions with Machine Learning ===
  
−
=== The Modulation Experiment: Data Analysis ===
+
It has been known for more than three decades that the parton distribution functions (PDFs) of nucleons bound within heavy nuclei are modified with respect to their free-nucleon counterparts. Despite active experimental and theoretical investigations, the underlying mechanisms that drive these in-medium modifications of nucleon substructure have yet to be fully understood.  The determination of nuclear PDFs is a topic of high relevance in order both to improve our fundamental understanding of the strong interactions in the nuclear environment, as well as and for the interpretation of heavy ion collisions at RHIC and the LHC, in particular for the characterization of the Quark-Gluon Plasma. The goal of this project is to exploit Machine Learning and Artificial Intelligence tools [1,2] (neural networks trained by stochastic gradient descent) to pin down the initial state of heavy ion collisions  by using recent measurements from proton-lead collisions at the LHC. Emphasis will be put on the poorly-known nuclear modifications of the gluon PDFs, which are still mostly ''terra incognita'' and highly relevant for phenomenological applications. In addition to theory calculations, the project will also involve code development using modern AI/ML tools such as TensorFlow and Keras.
  
−
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.
+
[1] https://arxiv.org/abs/1811.05858
 +
[2] https://arxiv.org/abs/1410.8849
  
−
''Contact: [mailto:z37@nikhef.nl Auke Colijn]''
+
''Contact: [mailto:j.rojo@vu.nl Juan Rojo]"
  
−
=== Theory:  Stress-testing the Standard Model at the high-energy frontier ===
 
  
−
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.
+
=== Dark Matter: XENON1T 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 building 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 data from the XENON1T detector. The work will consist of understanding the detector signals and applying machine learning tools such as deep neutral networks to improve the reconstruction performance in our Python-based analysis tool, following the approach described in arXiv:1804.09641. The final goal is to improve the energy and position reconstruction uncertainties for the dark matter search. There will also be opportunity to do data-taking shifts at the Gran Sasso underground laboratory in Italy.  
  
−
''Contact: [mailto:j.rojo@vu.nl Juan Rojo]''
+
''Contact: [mailto:decowski@nikhef.nl Patrick Decowski] and [mailto:z37@nikhef.nl Auke Colijn]''
  
−
=== Theory:  The quark and gluon internal structure of heavy nuclei in the LHC era  ===
+
=== Dark Matter: 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 plan to use this detector for the development of new detection techniques (such as utilizing new photosensors) and to improve the understanding of the response of liquid xenon to various forms of radiation. The results could be directly used in the XENON experiment, the world’s most sensitive direct detection dark matter experiment at the Gran Sasso underground laboratory. 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.
  
−
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).  
+
''Contact: [mailto:decowski@nikhef.nl Patrick Decowski] and [mailto:z37@nikhef.nl Auke Colijn]''
  
−
"Further information [[http://pcteserver.mi.infn.it/~nnpdf/VU/2018-MasterProject-nPDFs.pdf here]]
+
=== Dark Matter: 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 2025, 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:j.rojo@vu.nl Juan Rojo]''
+
''Contact: [mailto:decowski@nikhef.nl Patrick Decowski] and [mailto:z37@nikhef.nl Auke Colijn]''
  
−
=== Theory: Combined QCD analysis of parton distribution and fragmentation functions ===
+
=== The Modulation Experiment: Data Analysis ===
 +
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.
  
−
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.
+
''Contact: [mailto:z37@nikhef.nl Auke Colijn]''
  
−
"Further information [[http://pcteserver.mi.infn.it/~nnpdf/VU/2018-MasterProject-FFpPDFs.pdf here]]
+
=== ATLAS : Excited lepton searches with multiple leptons ===
  
−
''Contact: [mailto:j.rojo@vu.nl Juan Rojo]''
+
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).
  
 +
''Contact: [mailto:O.Igonkina@nikhef.nl Olya Igonkina and Marcus Morgenstern and Pepijn Bakker]''
  
−
=== (ALICE) Charm is in the Quark Gluon Plasma ===
+
=== ATLAS : A search for lepton non-universality in Bc meson decays ===
−
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]''
+
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).
  
−
=== (ALICE) Probing the time evolution of particle production in the Quark-Gluon Plasma ===
+
''Contact: [mailto:O.Igonkina@nikhef.nl Olya Igonkina and JJ Teoh]''
−
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]''
 
  
−
=== (ALICE) CP violating effects in QCD: looking for the chiral magnetic effect with ALICE at the LHC ===
+
=== LHCb :  Measurement of Central Exclusive Production Rates of Chi_c using converted photons in LHCb ===
−
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]''
+
Central exclusive production (CEP) of particles at the LHC is characterised by a extremely clean signature. Differently from the typical inelastic collisions where many particles are created resulting in a so-called Primary Vertex, CEP events have only the final state particles of interest. In this project the particle of interest is a pair of charmed quarks creating a chi_c particle. In theory this process is generated by a long range gluon exchange and can elucidate the nature of the strong force, described by the quantum chromodynamics in the the standard model. The proposed work involves  analysing a pre-existing dataset with reconstructed chi_c and simulating events at the LHCb in order to obtain the relative occurrence rate of each chi_c species (spins 0, 1, 2), a quantity that can be easily compared to theoretical predictions.
  
−
=== (ALICE) Particle polarisation in strong magnetic fields ===
+
"Contact: [mailto:K.Akiba@nikhef.nl Kazu Akiba]"
−
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]''
+
=== LHCb : Optimization studies for Vertex detector at the High Lumi LHCb  ===
  
 +
The LHCb experiment is dedicated to measure tiny differences between matter and antimatter through the precise study of rare processes involving b or c quarks.  The LHCb detector will undergo a major modification in order to dramatically increase the luminosity and be able to  measure indirect effects of physics beyond the standard model.  In this environment, over 42 simultaneous collisions are expected to happen at a time interval of 200 ps where the two proton bunches overlap. The particles of interest have a relatively long lifetime and therefore the best way to distinguish them from the background collisions is through the precise reconstruction of displaced vertices and pointing directions.  The new detector considers using extremely recent or even future technologies to measure space (with resolutions below 10 um) and time (100 ps or better) to efficiently reconstruct the events of interest for physics.  The project involves changing completely  the LHCb Vertex Locator (VELO) design in simulation and determine what can be the best performance for the upgraded detector, considering different spatial and temporal resolutions.
  
−
=== ATLAS : Double Higgs searches with multiple leptons ===
+
"Contact: [mailto:K.Akiba@nikhef.nl Kazu Akiba]"
  
−
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 reconstruct events with two Higgs bosons 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).
+
=== LHCb :  Measurement of charge multiplication in heavily irradiated sensors ===
  
−
''Contact: [mailto:O.Igonkina@nikhef.nl Olya Igonkina and Marcus Morgenstern and Pepijn Bakker]''
+
During the R&D phase for the LHCb VELO Upgrade detector a few sensor prototypes were irradiated to the extreme fluence expected to be achieved during the detector lifetime. These samples were tested using high energy particles at the SPS facility at CERN with their trajectories reconstructed by the Timepix3 telescope. A preliminary analysis revealed that at the highest irradiation levels the amount of signal observed is higher than expected, and even larger than the signal obtained at lower doses.  At the Device Under Test (DUT) position inside the telescope, the spatial resolution attained by this system is below 2 um. This means that a detailed analysis can be performed in order to study where and how this signal amplification happens within  the 55x55 um^2 pixel cell.  This project involves analysing the telescope and DUT data to investigate the charge multiplication mechanism at the microscopic level.
  
−
=== ATLAS : A search for lepton flavor violation with tau decays ===
+
"Contact: [mailto:K.Akiba@nikhef.nl Kazu Akiba]"
  
−
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
 
−
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).
 
  
−
''Contact: [mailto:O.Igonkina@nikhef.nl Olya Igonkina and Edwin Chow]''
 
  
  
−
=== ATLAS : A search for lepton non-universality in Bc meson decays ===
 
  
−
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).
+
== Projects with September 2018 start ==
  
−
''Contact: [mailto:O.Igonkina@nikhef.nl Olya Igonkina and Edwin Chow]''
 
  
  
−
=== LHCb: Searching for dark matter in exotic six-quark particles ===
+
=== Theory: Stress-testing the Standard Model at the high-energy frontier ===
−
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]''
+
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.
  
−
=== Virgo: Searching for gravitational waves from compact binary coalescence ===
+
''Contact: [mailto:j.rojo@vu.nl Juan Rojo]''
  
−
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.
+
=== Theory:  The quark and gluon internal structure of heavy nuclei in the LHC era  ===
  
−
''Contact: [mailto:caudills@nikhef.nl Sarah Caudill]''
+
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).  
  
 +
"Further information [[http://pcteserver.mi.infn.it/~nnpdf/VU/2018-MasterProject-nPDFs.pdf here]]
  
−
=== Detector R&D: Spectral X-ray imaging - Looking at colours the eyes can't see ===
+
''Contact: [mailto:j.rojo@vu.nl Juan Rojo]''
  
−
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.
+
=== Theory:  Combined QCD analysis of parton distribution and fragmentation functions ===
  
−
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.
+
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.
  
−
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).
+
"Further information [[http://pcteserver.mi.infn.it/~nnpdf/VU/2018-MasterProject-FFpPDFs.pdf here]]
  
−
Some activities that students can work on:  
+
''Contact: [mailto:j.rojo@vu.nl Juan Rojo]''
  
−
- Medical X-ray imaging (CT and ‘flat’ X-ray images): Detection of iodine contrast agent. Detection of calcifications (hint for a tumour).
 
  
−
- Material research: Using spectral information to identify materials and recognise compounds.
+
=== 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.  
  
−
- Determine how much existing applications can benefit from spectral X-ray imaging and look for potential new applications.
+
''Contact: [mailto:Panos.Christakoglou@nikhef.nl Panos Christakoglou and Paul Kuijer]''
  
−
- Characterise, calibrate, optimise X-ray imaging detector systems.  
+
=== ALICE: Probing the time evolution of particle production in the Quark-Gluon Plasma ===
 +
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:d77@nikhef.nl Els Koffeman], [mailto:martinfr@nikhef.nl Martin Fransen]''
+
''Contact: [mailto:Panos.Christakoglou@nikhef.nl Panos Christakoglou]''
  
−
=== Detector R&D: Compton camera ===
+
=== ALICE: CP violating effects in QCD: looking for the chiral magnetic effect with ALICE at the LHC ===
 +
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.
  
−
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.
+
''Contact: [mailto:Panos.Christakoglou@nikhef.nl Panos Christakoglou]''
  
−
''Contact: [mailto:d77@nikhef.nl Els Koffeman]
+
=== 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 [https://arxiv.org/abs/1708.08951 arXiv:1708.08951]
  
−
=== Detector R&D: Holographic projector ===
+
''Contact: [mailto:patrick.koppenburg@cern.ch Patrick Koppenburg]''
  
−
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.
 
  
−
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...
+
=== LHCb: Measurement of BR(B0 → Ds+ Ds-) ===
  
−
The big question: How does the performance of the holographic emitter depend on sample density and sample positions?
+
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.
 +
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
  
−
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).
+
''Contact: [mailto:niels.tuning@nikhef.nl Niels Tuning], [mailto:m.veronesi@nikhef.nl Michele Veronesi (PhD)], [mailto:s.esen@nikhef.nl Sevda Esen (postdoc)]''
  
−
The aspects of a holographic image we are investigating are:
+
=== LHCb: Measurement of relative ratio of B+ → D0D+ and B+ → D0Ds decays ===
−
 
−
- Noise
 
  
−
- Contrast
+
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.
 +
Relevant information:
 +
[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
  
−
- Suppression of under sampling artefacts
+
''Contact: [mailto:niels.tuning@nikhef.nl Niels Tuning], [mailto:m.veronesi@nikhef.nl Michele Veronesi (PhD)], [mailto:s.esen@nikhef.nl Sevda Esen (postdoc)]''
  
−
- Resolution
 
−
 
−
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]
 
−
----
 
  
−
=== KM3NeT : Reconstruction of first neutrino interactions in KM3NeT ===
+
=== Virgo: Searching for gravitational waves from compact binary coalescence ===
  
−
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.
+
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.
  
−
Programming skills are essential, mostly root and C++ will be used.
+
''Contact: [mailto:caudills@nikhef.nl Sarah Caudill]''
  
−
'' Contact: [mailto:bruijn@nikhef.nl Ronald Bruijn]''
+
=== Virgo: Simulations of Binary Neutron Star Mergers and applications for multimessenger astronomy ===
  
−
=== ANTARES: Analysis of IceCube neutrino sources. ===
+
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.
 +
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:
  
−
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.
+
- the estimation of the ejected material released from the merger and the development of models for the electromagnetic signals
−
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.
+
- further improvement of gravitational waveform models including numerical relativity information
  
−
'' Contact: [mailto:dosamt@nikhef.nl Dorothea Samtleben]''
+
- further improvement of the construction of the initial conditions of binary neutron star simulations
  
−
== OLD Projects [from last year] ==
+
- code improvements of the evolution code incorporating additional microphysical aspects as magnetic fields, tabulated equation of states, or neutrino leakage schemes.
  
 +
- studying the merger properties of neutron stars with exotic objects as boson or axion stars. 
  
 +
''Contact: [mailto:diettim@nikhef.nl Tim Dietrich]''
  
−
=== The Modulation Experiment: Data Analysis ===
+
=== Virgo: Measuring cosmological parameters from gravitational-wave observations of compact binaries ===
  
−
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 an all-round physicist with interest in both lab-work and data-analysis. The student 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.
+
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.
  
−
''Contact: [mailto:z37@nikhef.nl Auke Colijn]''
+
''Contact: [mailto:archis@nikhef.nl Archisman Ghosh] and [mailto:vdbroeck@nikhef.nl Chris Van Den Broeck]''
  
−
=== The XENON Dark Matter Experiment: Data Analysis ===
+
=== Detector R&D: Spectral X-ray imaging - Looking at colours the eyes can't see ===
  
−
The XENON collaboration has started 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 data-analysis on this new detector. The work will consist of understanding the signals that come out of the detector and in particular focus on the so-called double scatter events. We are interested in developing methods in order to interpret the response of the detector better and are developing sophisticated statistical tools to do this. This work will include looking at data and developing new algorithms in our Python-based analysis tool. There will also be opportunity to do data-taking shifts at the Gran Sasso underground laboratory in Italy.  
+
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:decowski@nikhef.nl Patrick Decowski]''
+
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.
  
−
=== XAMS Dark Matter R&D Setup ===
+
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).
  
−
The Amsterdam Dark Matter group has built 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 plan to use this detector for the development of new detection techniques (such as utilizing new photosensors) and to improve the understanding of the response of liquid xenon to various forms of radiation. The results could be directly used in the XENON experiment, the world’s most sensitive direct detection dark matter experiment at the Gran Sasso underground laboratory. 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.
+
Some activities that students can work on:
  
−
''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).
  
−
=== LHCb: A Scintillator Fibers Tracker ===
+
- Material research: Using spectral information to identify materials and recognise compounds.
  
−
The LHCb collaboration is upgrading the present tracking system
+
- Determine how much existing applications can benefit from spectral X-ray imaging and look for potential new applications.  
−
constructing a new tracker based on scintillating fibers combined
 
−
with silicon photo-multipliers (SiPM): the SciFi Tracker!
 
−
Nikhef plays a key role in the project, as we will build the
 
−
SciFi fibers modules, the cold-box enclosure housing the SiPMs,
 
−
and a large part of the on-detector electronics. In all these
 
−
areas, interesting test hardware and software has to be realized,
 
−
and several research topics for a Master project are available,
 
−
taking the student in contact with state-of-the-art particle detectors,
 
−
in a large team of physicists and engineers. Possible collaborations
 
−
with the Nikhef R&D group can also be envisaged.
 
  
−
''Contact: [mailto:antonio@nikhef.nl Antonio Pellegrino]''
+
- Characterise, calibrate, optimise X-ray imaging detector systems.  
  
−
=== LHCb: Discovery of the Decay Lb --> p Ds+ ===
+
''Contact: [mailto:martinfr@nikhef.nl Martin Fransen]''
−
This project aims to measure the branching fraction of the decay Lb->p Ds+ (bud -> uud + ds).
 
−
The decay Lb->p Ds+ is quite rare, because it occurs through the transition of a b-quark to a u-quark.
 
−
It has not been measured yet (although some LHCb colleagues claim to have seen it).
 
−
This decay is interesting, because
 
  
−
1) It is sensitive to the b->u coupling (CKM-element Vub), which determination is heavily debated.
+
=== Detector R&D: Compton camera ===
−
2) It can quantify non-factorisable QCD effects in b-baryon decays.
 
  
−
The decay is closely related to B0->pi-Ds+, which proceeds through a similar Feynman diagram.
+
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.
−
Also, the final state of B0->pi-Ds+ is almost identical to Lb->p Ds+.  
 
−
The aim is to determine the relative branching fraction of Lb->pDs+ with respect to B0->D+pi- decays,
 
−
in close collaboration with the PhD (who will study BR(B0->pi-Ds+)/BR(B0->D+pi-) ).
 
−
This project will result in a journal publication on behalf of the LHCb collaboration, written by you.
 
−
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] R.Aaij et al. [LHCb Collaboration], ``Determination of the branching fractions of B0s->DsK and B0->DsK, JHEP 05 (2015) 019 [arXiv:1412.7654 [hep-ex]].
+
''Contact: [mailto:martinfr@nikhef.nl Martin Fransen]''
−
[2] R. Fleischer, N. Serra and N. Tuning, ``Tests of Factorization and SU(3) Relations in B Decays into Heavy-Light Final States, Phys. Rev. D 83, 014017 (2011) [arXiv:1012.2784 [hep-ph]].
 
  
−
''Contact: [mailto:h71@nikhef.nl Niels Tuning and Lennaert Bel and Mick Mulder]''
+
=== Detector R&D: Holographic projector ===
  
−
=== LHCb:  Measurement of B0 -> pi Ds- , the b -> u quark transition ===
+
A difficulty in generating holograms (based on the interference of light) is the required dense pixel pitch. One would need a pixel pitch of less than 200 nanometer. With larger pixels artefacts occur due to spatial under sampling. A pixel pitch of 200 nanometer 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.
  
−
This project aims to measure the branching fraction of the decay B0->pi Ds+.
+
A new holographic projection method has been developed that reduces under sampling artefacts for projectors with a ‘low’ pixel density. It is using '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 projector can be built with a significantly lower pixel density and correspondingly less required computing power. This could bring holography in reach for many applications like display, lithography, 3D printing, metrology, etc..
−
This decay is closely related to Lb->p Ds+ (see above), and close collaboration between the two master projects is foreseen.
+
−
This research was started by a previous master student.  
+
Of course, nothing comes for free: With less pixels, holograms become noisier and the contrast will be reduced. The big question: How do we determine the requirements (in terms of pixel density, pixel positioning, etc..) for the holographic projector based on requirements for the holograms?
−
The new measurement will finish the work, and include the new data from 2015 and 2016.
+
Requirements for a hologram can be expressed in terms of: Noise, contrast, resolution, suppression of under sampling artefacts, etc..  
  
−
See Mick Mulders [http://www.nikhef.nl/pub/experiments/bfys/lhcb/Theses/master/2015_MickMulder.pdf master thesis] for more information.
+
For this project we are building a proof of concept holographic emitter. This set-up will be used to verify simulation results (and also to project some cool holograms of course).  
  
−
''Contact: [mailto:h71@nikhef.nl Niels Tuning and Lennaert Bel and Mick Mulder]''
+
Students can do hands on lab-work (building and testing the proto type projector) and/or work on setting up simulation methods and models. Simulations in this field can be highly parallelized and are preferably written for parallel computing and/or GPU computing.
  
−
=== LHCb: A search for heavy neutrinos in the decay of W bosons at LHCb ===
 
  
−
Neutrinos are arguably the most mysterious of all known fundamental fermions as they are both much lighter than all others and only weakly interacting. It is thought that the tiny mass of neutrinos can be explained by their mixing with so-far unknown, much heavier, neutrino-like particles. In this research proposal we look for these new neutrinos in the decay of the SM W-boson using data with the LHCb experiment at CERN. The W boson is assumed to decay to a heavy neutrino and a muon. The heavy neutrino subsequently decays to a muon and a pair of quarks. Both like-sign and opposite-sign muon pairs will be studied. The result of the analysis will either be a limit on the production of the new neutrinos or the discovery of something entirely new.
+
''Contact: [mailto:martinfr@nikhef.nl Martin Fransen]
−
 
 
−
''Contact: [mailto:wouterh@nikhef.nl Wouter Hulsbergen and Elena Dall'Occo]''
 
−
 
 
−
 
 
−
=== ALICE : Particle polarisation in strong magnetic fields ===
 
−
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 and Panos Christakoglou]''
 
−
 
 
−
=== ALICE : Blast-Wave Model in heavy-ion collisions ===
 
−
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 elliptic flow. A reasonable reproduction of the same observables is also achieved with models that use parameterisations that resemble the hydrodynamical evolution of the system assuming a given freeze-out scenario, usually referred to as blast-wave models. The goal of this project is to work on different blast wave parametrisations, test their dependence on the input parameters and extend their applicability by including more observables studied in heavy-ion collisions in the global fit.
 
−
 
 
−
''Contact: [mailto:Panos.Christakoglou@nikhef.nl Panos Christakoglou and Paul Kuijer]''
 
−
 
 
−
=== ALICE : Higher Harmonic Flow ===
 
−
When two ions collide, if the impact parameter is not zero, the overlap region is not isotropic. This spatial anisotropy of the overlap region is transformed into an anisotropy in momentum space through interactions between partons and at a later stage between the produced particles. It was recently realized that the overlap region of the colliding nuclei exhibits an irregular shape. These irregularities originate from the initial density profile of nucleons participating in the collision which is not smooth and is different from one event to the other. The resulting higher order flow harmonics (e.g. v3, v4, and v5, usually referred to as triangular, quadrangular, and pentangular flow, respectively) and in particular their transverse momentum dependence are argued to be more sensitive probes than elliptic flow not only of the initial geometry and its fluctuations but also of shear viscosity over entropy density (η/s). The goal of this project is to study v3, v4, and v5 for identified particles in collisions of heavy-ions at the LHC.
 
−
 
 
−
''Contact: [mailto:Panos.Christakoglou@nikhef.nl Panos Christakoglou and Paul Kuijer]''
 
−
 
 
−
=== ALICE : Chiral Magnetic Effect and the Strong CP Problem ===
 
−
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 and Paul Kuijer]''
+
=== Detector R&D: Laser Interferometer Space Antenna (LISA) ===
  
−
=== DR&D : Medical X-ray Imaging ===
+
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.
−
With the upcoming of true multi-threshold X-Ray detectors the possibilities for Spectral Imaging with low dose, including spectral CT, is now a reality around the corner. The Medipix3RX chip, from the Medipix Collaboration (CERN) features up to 8 programmable thresholds which can select energy bins without a threshold scan. A number of projects could be derived from the R&D activities with the Medipix3RX within the Nikhef R&D group on X-ray imaging for medical applications:
 
−
* Medipix3RX characterization in all its operation modes and gains.  
 
−
* Spectral CT and scarce sampling 3D reconstruction
 
−
* Charge sharing: the charge-sum capabilities of the chip can be exploited to further understand the problem of charge sharing in pixelized detectors. A combination of the characterization of the charge-summing mode plus the use of both planar, and 3D sensors, at the light of MC simulation, could reveal valuable information about charge sharing.
 
  
−
''Contact: [mailto:koffeman@nikhef.nl Els Koffeman],[mailto:martinfr@nihef.nl Martin Fransen]''
+
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.
  
−
=== DR&D : Compton camera ===
+
Key words: LISA, space, gravitational waves, simulations, signal processing
−
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 succesfull 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.
 
  
−
''Contact: [mailto:koffeman@nikhef.nl Els Koffeman]''
+
''Contact: [mailto:nielsvb@nikhef.nl Niels van Bakel],[mailto:ernst-jan.buis@tno.nl  Ernst-Jan Buis]''
  
 
=== KM3NeT : Reconstruction of first neutrino interactions in KM3NeT ===
 
=== KM3NeT : Reconstruction of first neutrino interactions in KM3NeT ===
  
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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, in total 30 to be deployed til end of next year. 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.
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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.
 
Programming skills are essential, mostly root and C++ will be used.
Line 294: Line 250:
 
'' Contact: [mailto:dosamt@nikhef.nl Dorothea Samtleben]''
 
'' Contact: [mailto:dosamt@nikhef.nl Dorothea Samtleben]''
  
 +
=== VU LaserLaB: Measuring the electric dipole moment (EDM) of the electron ===
  
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=== ATLAS: Implementation of Morphing techniques for ATLAS top physics analysis. ===
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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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Perhaps the most promising gateway to physics beyond the Standard Model is the top quark, the heaviest elementary particle. Particularly
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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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interesting is how the different top quark spin states influence the angular distribution of electrons and other decays products, which can be measured very accurately. New interactions would alter this coupling, leading to decay patterns that are different from those predicted by
 
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the Standard Model. At Nikhef we are implementing NLO predictions of the so called dimension-6 operators to describe several measurable distributions. To confront these distributions with data, a continues parametrization is required. For this purpose, we want to introduce a novel technique in top quark analysis which is based on Morphing. The project consist of an implementation of Morphing to parametrize the top's angular distributions and to demonstrate that the paramdeters can be extracted in a fitting procedure using (pseudo)data.  
 
  
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Affinity with software is essential, mainly C++ and root will be used.  
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'' Contact: [mailto:H.L.Bethlem@vu.nl Rick Bethlem]''
  
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'' Contact: [mailto:h73@nikhef.nl Marcel Vreeswijk]''
 
  
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=== Theory – Probing electroweak symmetry breaking with Higgs pair production at the LHC and beyond ===
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=== VU LaserLab: Physics beyond the Standard model from molecules ===
  
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The measurement of Higgs pair production will be a cornerstone of the LHC program in the coming years. Double Higgs production provides a crucial window upon the mechanism of electroweak symmetry breaking, and has a unique sensitivity to a number of currently unknown Higgs couplings, like the Higgs self-coupling λ and the coupling between a pair of Higgs bosons and two vector bosons. In this project, the student will explore the feasibility of the measurement of Higgs pair production in the 4b final state both at the LHC and at future 100 TeV collider. A number of production modes will be considered, including gluon-fusion, vector-boson-fusion, as well as Higgs pair production in association with a top-quark pair. A key ingredient of the project will be the exploitation of multivariate techniques such as Artificial Neural Networks and other multivariate discriminants to enhance the ratio of di-Higgs signal over backgrounds.  
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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.
  
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The project involves to estimate the precision that can be achieved in the extraction of the Higgs self-coupling for a number of assumptions about the performance of the LHC detectors, and in particular to quantify the information that can be extracted from the Run II dataset with L = 300 1/fb . A similar approach will be applied to the determination of other unknown properties of the Higgs sector, such as the coupling between two Higgs bosons and two weak vector bosons, as well as the Wilson coefficients of higher-dimensional operators in the Standard Model Effective Field Theory (SM-EFT). Additional information on this project can be found here: [http://pcteserver.mi.infn.it/~nnpdf/VU/2017-MasterProject-HH.pdf].
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In the past half year we have produced a number of important results that are described in
 +
the following papers:
 +
* Frequency comb (Ramsey type) electronic  excitations in the H2 molecule:
 +
see: Deep-ultraviolet frequency metrology of H2 for tests of molecular quantum theory
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http://www.nat.vu.nl/~wimu/Publications/Altmann-PRL-2018.pdf
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* ''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
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* ''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
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* ''Dissociation energy of the hydrogen molecule at 10^-9 accuracy'' paper submitted to Phys. Rev. Lett.
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* ''Probing QED and fundamental constants through laser spectroscopy of vibrational transitions in HD+''
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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
  
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''Contact: [mailto:j.rojo@vu.nl Juan Rojo]''
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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:
 +
* Performing calculations of hyperfine structures
  
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=== Theory – Constraining the proton structure with Run II LHC data ===
+
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.
  
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The non-perturbative dynamics that determine the energy distribution of quarks and gluons inside protons, the so-called parton distribution functions (PDFs), cannot be computed from first principles from Quantum Chromodynamics (QCD), and need to be determined from experimental data. PDFs are an essential ingredient for the scientific program at the Large Hadron Collider (LHC), from Higgs characterisation to searches for New Physics beyond the Standard Model. One recent breakthrough in PDF analysis has been the exploitation of the constraints from LHC data. From direct photons to top quark pair production cross-sections and charmed meson differential distributions, LHC measurements are now a central ingredient of PDF fits, providing important information on poorly-known PDFs such as the large and small-x gluon or the large-x antiquarks. With the upcoming availability of data from the Run II of the LHC, at a center-of-mass energy of 13 TeV, these constraints are expected to become even more stringent.
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'' 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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In this project, the implications of PDF-sensitive measurements at the LHC 13 TeV will be quantified. Processes that will be considered include jet and dijet production at the multi-TeV scale, single-top quark production, and weak boson production in association with heavy quarks, among several others. These studies will be performed using the NNPDF fitting framework, based on artificial neural networks and genetic algorithms. The  phenomenological implications of the improved PDF modelling for Higgs and new physics searches at the LHC will also be explored. Additional information on this project can be found here: [http://pcteserver.mi.infn.it/~nnpdf/talks/MSc_projects/2017-MasterProject-PDFs.pdf].
 
  
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''Contact: [mailto:j.rojo@vu.nl Juan Rojo]''
 
  
  
 
[[Last years MSc Projects|Last year's MSc Projects]]
 
[[Last years MSc Projects|Last year's MSc Projects]]

Revision as of 16:27, 19 March 2019

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 September 2019 start

Theory: The Effective Field Theory Pathway to New Physics at the LHC

A very promising framework to parametrise in a robust and model-independent way deviations from the Standard Model (SM) induced by new heavy particles is the Standard Model Effective Field Theory (SMEFT). In this formalism, Beyond the SM effects are encapsulated in higher-dimensional operators constructed from SM fields respecting their symmetry properties. In this project, we aim to carry out a global analysis of the SMEFT from high-precision LHC data, including Higgs boson production, flavour observables, and low-energy measurements. This analysis will be carried out in the context of the recently developed SMEFiT approach [1] based on Machine Learning techniques to efficiently explore the complex theory parameter space. The ultimate goal is either to uncover glimpses of new particles or interactions at the LHC, or to derive the most stringent model-independent bounds to date on general theories of New Physics.

Contact: Juan Rojo"

[1] https://arxiv.org/abs/1901.05965

Theory: Pinning down the initial state of heavy-ion collisions with Machine Learning

It has been known for more than three decades that the parton distribution functions (PDFs) of nucleons bound within heavy nuclei are modified with respect to their free-nucleon counterparts. Despite active experimental and theoretical investigations, the underlying mechanisms that drive these in-medium modifications of nucleon substructure have yet to be fully understood. The determination of nuclear PDFs is a topic of high relevance in order both to improve our fundamental understanding of the strong interactions in the nuclear environment, as well as and for the interpretation of heavy ion collisions at RHIC and the LHC, in particular for the characterization of the Quark-Gluon Plasma. The goal of this project is to exploit Machine Learning and Artificial Intelligence tools [1,2] (neural networks trained by stochastic gradient descent) to pin down the initial state of heavy ion collisions by using recent measurements from proton-lead collisions at the LHC. Emphasis will be put on the poorly-known nuclear modifications of the gluon PDFs, which are still mostly terra incognita and highly relevant for phenomenological applications. In addition to theory calculations, the project will also involve code development using modern AI/ML tools such as TensorFlow and Keras.

[1] https://arxiv.org/abs/1811.05858 [2] https://arxiv.org/abs/1410.8849

Contact: Juan Rojo"


Dark Matter: XENON1T 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 building 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 data from the XENON1T detector. The work will consist of understanding the detector signals and applying machine learning tools such as deep neutral networks to improve the reconstruction performance in our Python-based analysis tool, following the approach described in arXiv:1804.09641. The final goal is to improve the energy and position reconstruction uncertainties for the dark matter search. 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: 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 plan to use this detector for the development of new detection techniques (such as utilizing new photosensors) and to improve the understanding of the response of liquid xenon to various forms of radiation. The results could be directly used in the XENON experiment, the world’s most sensitive direct detection dark matter experiment at the Gran Sasso underground laboratory. 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: 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 2025, 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

The Modulation Experiment: Data Analysis

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.

Contact: Auke Colijn

ATLAS : Excited lepton searches with multiple leptons

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).

Contact: Olya Igonkina and Marcus Morgenstern and Pepijn Bakker

ATLAS : A search for lepton non-universality in Bc meson decays

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).

Contact: Olya Igonkina and JJ Teoh


LHCb : Measurement of Central Exclusive Production Rates of Chi_c using converted photons in LHCb

Central exclusive production (CEP) of particles at the LHC is characterised by a extremely clean signature. Differently from the typical inelastic collisions where many particles are created resulting in a so-called Primary Vertex, CEP events have only the final state particles of interest. In this project the particle of interest is a pair of charmed quarks creating a chi_c particle. In theory this process is generated by a long range gluon exchange and can elucidate the nature of the strong force, described by the quantum chromodynamics in the the standard model. The proposed work involves analysing a pre-existing dataset with reconstructed chi_c and simulating events at the LHCb in order to obtain the relative occurrence rate of each chi_c species (spins 0, 1, 2), a quantity that can be easily compared to theoretical predictions.

"Contact: Kazu Akiba"

LHCb : Optimization studies for Vertex detector at the High Lumi LHCb

The LHCb experiment is dedicated to measure tiny differences between matter and antimatter through the precise study of rare processes involving b or c quarks. The LHCb detector will undergo a major modification in order to dramatically increase the luminosity and be able to measure indirect effects of physics beyond the standard model. In this environment, over 42 simultaneous collisions are expected to happen at a time interval of 200 ps where the two proton bunches overlap. The particles of interest have a relatively long lifetime and therefore the best way to distinguish them from the background collisions is through the precise reconstruction of displaced vertices and pointing directions. The new detector considers using extremely recent or even future technologies to measure space (with resolutions below 10 um) and time (100 ps or better) to efficiently reconstruct the events of interest for physics. The project involves changing completely the LHCb Vertex Locator (VELO) design in simulation and determine what can be the best performance for the upgraded detector, considering different spatial and temporal resolutions.

"Contact: Kazu Akiba"

LHCb : Measurement of charge multiplication in heavily irradiated sensors

During the R&D phase for the LHCb VELO Upgrade detector a few sensor prototypes were irradiated to the extreme fluence expected to be achieved during the detector lifetime. These samples were tested using high energy particles at the SPS facility at CERN with their trajectories reconstructed by the Timepix3 telescope. A preliminary analysis revealed that at the highest irradiation levels the amount of signal observed is higher than expected, and even larger than the signal obtained at lower doses. At the Device Under Test (DUT) position inside the telescope, the spatial resolution attained by this system is below 2 um. This means that a detailed analysis can be performed in order to study where and how this signal amplification happens within the 55x55 um^2 pixel cell. This project involves analysing the telescope and DUT data to investigate the charge multiplication mechanism at the microscopic level.

"Contact: Kazu Akiba"



Projects with September 2018 start

Theory: Stress-testing the Standard Model at the high-energy frontier

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.

Contact: Juan Rojo

Theory: The quark and gluon internal structure of heavy nuclei in the LHC era

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).

"Further information [here]

Contact: Juan Rojo

Theory: Combined QCD analysis of parton distribution and fragmentation functions

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 [here]

Contact: Juan Rojo


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: Panos Christakoglou and Paul Kuijer

ALICE: Probing the time evolution of particle production in the Quark-Gluon Plasma

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: Panos Christakoglou

ALICE: CP violating effects in QCD: looking for the chiral magnetic effect with ALICE at the LHC

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: Panos Christakoglou

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


LHCb: Measurement of BR(B0 → Ds+ Ds-)

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. 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: Niels Tuning, Michele Veronesi (PhD), Sevda Esen (postdoc)

LHCb: Measurement of relative ratio of B+ → D0D+ and B+ → D0Ds decays

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. Relevant information: [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: Niels Tuning, Michele Veronesi (PhD), Sevda Esen (postdoc)


Virgo: Searching for gravitational waves from compact binary coalescence

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.

Contact: Sarah Caudill

Virgo: Simulations of Binary Neutron Star Mergers and applications for multimessenger astronomy

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. 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:

- the estimation of the ejected material released from the merger and the development of models for the electromagnetic signals

- further improvement of gravitational waveform models including numerical relativity information

- further improvement of the construction of the initial conditions of binary neutron star simulations

- code improvements of the evolution code incorporating additional microphysical aspects as magnetic fields, tabulated equation of states, or neutrino leakage schemes.

- studying the merger properties of neutron stars with exotic objects as boson or axion stars.

Contact: Tim Dietrich

Virgo: Measuring cosmological parameters from gravitational-wave observations of compact binaries

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.

Contact: Archisman Ghosh and Chris Van Den Broeck

Detector R&D: Spectral X-ray imaging - Looking at colours the eyes can't see

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.

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.

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).

Some activities that students can work on:

- Medical X-ray imaging (CT and ‘flat’ X-ray images): Detection of iodine contrast agent. Detection of calcifications (hint for a tumour).

- Material research: Using spectral information to identify materials and recognise compounds.

- Determine how much existing applications can benefit from spectral X-ray imaging and look for potential new applications.

- Characterise, calibrate, optimise X-ray imaging detector systems.

Contact: Martin Fransen

Detector R&D: Compton camera

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.

Contact: Martin Fransen

Detector R&D: Holographic projector

A difficulty in generating holograms (based on the interference of light) is the required dense pixel pitch. One would need a pixel pitch of less than 200 nanometer. With larger pixels artefacts occur due to spatial under sampling. A pixel pitch of 200 nanometer 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.

A new holographic projection method has been developed that reduces under sampling artefacts for projectors with a ‘low’ pixel density. It is using '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 projector can be built with a significantly lower pixel density and correspondingly less required computing power. This could bring holography in reach for many applications like display, lithography, 3D printing, metrology, etc..

Of course, nothing comes for free: With less pixels, holograms become noisier and the contrast will be reduced. The big question: How do we determine the requirements (in terms of pixel density, pixel positioning, etc..) for the holographic projector based on requirements for the holograms? Requirements for a hologram can be expressed in terms of: Noise, contrast, resolution, suppression of under sampling artefacts, etc..

For this project we are building a proof of concept holographic emitter. This set-up will be used to verify simulation results (and also to project some cool holograms of course).

Students can do hands on lab-work (building and testing the proto type projector) and/or work on setting up simulation methods and models. Simulations in this field can be highly parallelized and are preferably written for parallel computing and/or GPU computing.


Contact: Martin Fransen

Detector R&D: Laser Interferometer Space Antenna (LISA)

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.

Key words: LISA, space, gravitational waves, simulations, signal processing

Contact: Niels van Bakel,Ernst-Jan Buis

KM3NeT : Reconstruction of first neutrino interactions in KM3NeT

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.

Contact: Ronald Bruijn

ANTARES: Analysis of IceCube neutrino sources.

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. 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.

Contact: Dorothea Samtleben

VU LaserLaB: Measuring the electric dipole moment (EDM) of the electron

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!

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.

Contact: Rick Bethlem


VU LaserLab: Physics beyond the Standard model from molecules

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.

In the past half year we have produced a number of important results that are described in the following papers:

  • Frequency comb (Ramsey type) electronic excitations in the H2 molecule:

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:

  • 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: Wim Ubachs Kjeld Eikema Rick Bethlem



Last year's MSc Projects

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