Master Projects

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(New Projects [start in September 2018])
(LHCb: Searching for dark matter in exotic six-quark particles)
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=== LHCb: Measurement of BR(B0 -> Ds+ Ds-)  
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=== 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.
 
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(*).
 
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(*).
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''Contact: [mailto:niels.tuning@nikhef.nl Niels Tuning], [mailto:m.veronesi@nikhef.nl Michele Veronesi (PhD)], [mailto:s.esen@nikhef.nl Sevda Esen (postdoc)]''
 
''Contact: [mailto:niels.tuning@nikhef.nl Niels Tuning], [mailto:m.veronesi@nikhef.nl Michele Veronesi (PhD)], [mailto:s.esen@nikhef.nl Sevda Esen (postdoc)]''
  
=== LHCb: Measurement of relative ratio of B+ → D0D+ and B+ -> D0Ds decays
+
=== 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.
 
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:  
 
Relevant information:  
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''Contact: [mailto:niels.tuning@nikhef.nl Niels Tuning], [mailto:m.veronesi@nikhef.nl Michele Veronesi (PhD)], [mailto:s.esen@nikhef.nl Sevda Esen (postdoc)]''
 
''Contact: [mailto:niels.tuning@nikhef.nl Niels Tuning], [mailto:m.veronesi@nikhef.nl Michele Veronesi (PhD)], [mailto:s.esen@nikhef.nl Sevda Esen (postdoc)]''
 
  
 
=== Virgo: Searching for gravitational waves from compact binary coalescence ===
 
=== Virgo: Searching for gravitational waves from compact binary coalescence ===

Revision as of 10:19, 12 April 2018

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.


Contents

New Projects [start in September 2018]

The XENON Dark Matter Experiment: Data Analysis

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.

Contact: Patrick Decowski

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

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

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: Paul Kuijer


ATLAS : Double Higgs 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 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).

Contact: Olya Igonkina and Marcus Morgenstern and Pepijn Bakker

ATLAS : A search for lepton flavor violation with tau decays

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: 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).

Contact: Olya Igonkina and Edwin Chow


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


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: Els Koffeman, 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: Els Koffeman

Detector R&D: Holographic projector

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...

The big question: How does the performance of the holographic emitter depend on sample density and sample positions?

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).

The aspects of a holographic image we are investigating are:

- Noise

- Contrast

- Suppression of under sampling artefacts

- 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: 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

OLD Projects [from last year]

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 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.

Contact: Auke Colijn

The XENON Dark Matter Experiment: Data Analysis

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.

Contact: Patrick Decowski

XAMS Dark Matter R&D Setup

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.

Contact: Patrick Decowski

LHCb: A Scintillator Fibers Tracker

The LHCb collaboration is upgrading the present tracking system 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: Antonio Pellegrino

LHCb: Discovery of the Decay Lb --> p Ds+

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. 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. 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]]. [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: Niels Tuning and Lennaert Bel and Mick Mulder

LHCb: Measurement of B0 -> pi Ds- , the b -> u quark transition

This project aims to measure the branching fraction of the decay B0->pi Ds+. 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. The new measurement will finish the work, and include the new data from 2015 and 2016.

See Mick Mulders master thesis for more information.

Contact: Niels Tuning and Lennaert Bel and Mick Mulder

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: 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: 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: 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: 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: Panos Christakoglou and Paul Kuijer

DR&D : Medical X-ray Imaging

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: Els Koffeman,Martin Fransen

DR&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 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: Els Koffeman

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, 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.

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


ATLAS: Implementation of Morphing techniques for ATLAS top physics analysis.

Perhaps the most promising gateway to physics beyond the Standard Model is the top quark, the heaviest elementary particle. Particularly 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 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.

Affinity with software is essential, mainly C++ and root will be used.

Contact: Marcel Vreeswijk

Theory – Probing electroweak symmetry breaking with Higgs pair production at the LHC and beyond

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.

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: [1].

Contact: Juan Rojo

Theory – Constraining the proton structure with Run II LHC data

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.

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: [2].

Contact: Juan Rojo


Last year's MSc Projects

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