Master Projects

Master Thesis Research Projects

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

Projects with a 2022 start

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

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

Contact: Panos Christakoglou and Alessandro Grelli and Marco van Leeuwen

ALICE: Searching for the strongest magnetic field in nature

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

Contact: Panos Christakoglou

ALICE: Looking for parity violating effects in strong interactions

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

Contact: Panos Christakoglou

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

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

Contact: Panos Christakoglou and Alessandro Grelli

ATLAS: The Higgs boson's self-coupling

The coupling of the Higgs boson to itself is one of the main unobserved interactions of the Standard Model and its observation is crucial to understand the shape of the Higgs potential. Here we propose to study the 'ttHH' final state: two top quarks and two Higgs bosons produced in a single collision. This topology is yet unexplored at the ATLAS experiment and the project consists of setting up the new analysis (including multivariate analysis techniques to recognise the complicated final state), optimising the sensitivity and including the result in the full ATLAS study of the Higgs boson's coupling to itself. With the LHC data from the upcoming Run-3, we might be able to see its first glimpses!

Contact: Tristan du Pree

ATLAS: The Next Generation

After the observation of the coupling of Higgs bosons to fermions of the third generation, the search for the coupling to fermions of the second generation is one of the next priorities for research at CERN's Large Hadron Collider. The search for the decay of the Higgs boson to two charm quarks is very new [1] and we see various opportunities for interesting developments. For this project we propose improvements in reconstruction (using exclusive decays) and advanced analysis techiques (using deep learning methods).

[1]https://atlas.cern/updates/briefing/charming-Higgs-decay

Contact: Tristan du Pree

ATLAS: Searching for new particles in very energetic diboson production

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

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

Contact: Flavia de Almeida Dias

ATLAS top-quark and Higgs-boson analysis combination, and Effective Field Theory interpretation

We are looking for a master student with interest in theory and data-analysis in the search for physics beyond the Standard Model in the top-quark and Higgs-boson sectors.

Your master-project starts just at the right time for preparing the Run-3 analysis of the ATLAS experiment at the LHC. In Run-3 (2022-2026), three times more data becomes available, enabling analysis of rare processes with innovative software tools and techniques.

This project aims to explore the newest strategy to combine the top-quark and Higgs-boson measurements in the perspective of constraining the existence of new physics beyond the Standard Model (SM) of Particle Physics. We selected the pp->tZq and gg->HZ processes as promising candidates for a combination to constrain new physics in the context of Standard Model Effective Field Theory (SMEFT). SMEFT is the state-of-the-art framework for theoretical interpretation of LHC data. In particular, you will study the SMEFT OtZ and Ophit operators, which are not well constrained by current measurements.

Besides affinity with particle physics theory, the ideal candidate for this project has developed python/C++ skills and is eager to learn advanced techniques. You start with a simulation of the signal and background samples using existing software tools. Then, an event selection study is required using Machine Learning techniques. To evaluate the SMEFT effects, a fitting procedure based on the innovative Morphing technique is foreseen, for which the basic tools in the ROOT and RooFit framework are available. The work is carried out in the ATLAS group at Nikhef and may lead to an ATLAS note.

Contact: > Geoffrey Gilles and Wouter Verkerke and Marcel Vreeswijk

ATLAS Machine learning to enhance reconstruction of very rare Higgs decays

Since the Higgs boson discovery in 2012 at the ATLAS experiment, the investigation of the properties of the Higgs boson has been a priority for research at the Large Hadron Collider (LHC). However, there are still a many open questions: Is the Higgs boson the only origin of Electroweak Symmetry Breaking? Is there a mechanism which can explain the observed mass pattern of SM particles? Many of these questions are linked to the Higgs boson coupling structure.

While the Higgs boson coupling to fermions of the third generation has been clearly, the investigation of the Higgs boson coupling to the light fermions of the second generation will be a major project for the upcoming data-taking period starting this year. The Higgs boson decay to muons is most sensitive channel to establish a coupling of the Higgs boson to second generation fermions. In this project you will work on an improvement of the H-->mumu search: In about 5% of the events, a photon is radiated off the outgoing muons. By recognizing these photons and taking their effect into account we can improve the reconstruct these events better. For this project we will use machine learning to best identify these special events and to take their energy contribution into account to improve the overall sensitivity.

Contact: Oliver Rieger and Wouter Verkerke and Peter Kluit

ATLAS: Scrutinising Higgs decaying into W bosons

Observation of the Higgs boson happened 10 years ago and since then scientists’ interest has shifted towards measuring precisely its properties. An example is a coupling strength telling us how does the Higgs boson interact with different particles such as W bosons. Measuring H→ WW →lnu lnu process allows us to not only probe the Standard Model (SM), by measuring the coupling strength or indirectly probe Higgs boson width, but also test against the theories beyond (for instance in the context of the effective field theory framework).

The student will take active part in the ATLAS HWW group. There are multiple possible areas of contribution within the group depending on the interest of the student. For instance, utilising machine learning techniques to optimise for the selection of HWW signal process, determining the fake background processes, interpreting the results through the beyond SM theories and others. Contact: Matouš Vozák and Ivo van Vulpen

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

The Amsterdam Dark Matter group operates an R&D xenon detector at Nikhef. The detector is a dual-phase xenon time-projection chamber and contains about 0.5kg of ultra-pure liquid xenon in the central volume. We use this detector for the development of new detection techniques - such as utilizing our newly installed silicon photomultipliers - and to improve the understanding of the response of liquid xenon to various forms of radiation. The results could be directly used in the XENONnT experiment, the world’s most sensitive direct detection dark matter experiment at the Gran Sasso underground laboratory, or for future Dark Matter experiments like DARWIN. We have several interesting projects for this facility. We are looking for someone who is interested in working in a laboratory on high-tech equipment, modifying the detector, taking data and analyzing the data themselves You will "own" this experiment.

Contact: Patrick Decowski and Auke Colijn

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

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

Contact: Patrick Decowski and Auke Colijn

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

DARWIN is the “ultimate” direct detection dark matter experiment, with the goal to reach the so-called “neutrino floor”, when neutrinos become a hard-to-reduce background. The large and exquisitely clean xenon mass will allow DARWIN to also be sensitive to other physics signals such as solar neutrinos, double-beta decay from Xe-136, axions and axion-like particles etc. While the experiment will only start in 2027, we are in the midst of optimizing the experiment, which is driven by simulations. We have an opening for a student to work on the GEANT4 Monte Carlo simulations for DARWIN. 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: Tina Pollmann, Patrick Decowski or Auke Colijn

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

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

Contact: Tina Pollmann and Patrick Decowski

Detector R&D: Time resolution of ultrathin monolithic timing detectors

For the upgrade of ALICE and LHCb vertex detectors, new silicon pixel detectors are being developed now that can register the passing particles with a time precision of tens of picoseconds. ALICE is the first experiment at the LHC to have installed monolithic sensors where electronics is integrated into the sensor. New prototypes of their sensors have arrived at Nikhef. New prototypes of other sensors able to withstand very high radiation fluences of the LHC are arriving soon. In this project, you will tackle the challenge to accurately measure the time resolution of one of these sensors with our laser setups in the laboratory. You will have the chance to work in an international collaboration where you will report about the performance of these novel sensors. There may even be an opportunity to join beam tests at CERN. For this project, we are looking for someone who is interested to work with high-tech sensors and equipment in our Nikhef laboratory and with python programming skills.

Contact: Jory Sonneveld

Detector R&D: Performance of monolithic sensors for the ALICE upgrade from test beam data

For the upgrade of the ALICE detector, ultrathin picosecond timing integrated sensors are being developed now, of which the first prototypes are now at Nikhef and are being studied in test beams at CERN and DESY in Hamburg. Sensors are studied with the ALPIDE (ALICE PIxel DEtector) telescope that uses the same sensors that have recently installed in the heart of the ALICE experiment at CERN. In this project, you will analyze data from beam tests to measure the efficiency and time resolution of the new prototypes for the ALICE upgrade with the latest data from test beams at CERN. If the travel situation allows, you will have the opportunity to join the ALICE test beam group at CERN or in Hamburg at DESY to take part in the exciting experience of taking real data. We are looking for someone with good programming and data analysis skills.

Contact: Jory Sonneveld

Detector R&D: Modeling radiation damage in silicon sensors

In the coming years, the ATLAS experiment at the LHC works on upgrades to prepare for the high-luminosity LHC, where many more collisions will take place than today. Both analysis of data and decisions made in preparation of these detectors and on data taking heavily rely on simulations, especially those that model the damage done to sensors after many collisions. It may sound counterintuitive, but particle detectors do not actually like particles: after many collisions at the LHC, a silicon pixel detector has seen so many particles that its bulk gathers defects. Charge generated by traversing particles can get trapped in defects resulting in less charge induced in the readout electrodes, reducing detector performance in resolution and efficiency. In this project, you will be a member of the international ATLAS collaboration where you will compare different models of radiation damage with measured data. You will learn technology computer aided design (TCAD), widely used in industry, and contribute to the open source program Allpix Squared that is widely used for simulations in many areas of particle physics. Here we are looking for someone with good programming and data analysis skills who would like to contribute to upgrades of collider experiments.

Contact: Jory Sonneveld

Detector R&D: Fast trigger

Muons in cosmic rays are for free! In this project we are not looking for where cosmic rays come from or what physics can be studied with them. Instead, we are using them to test some of our particle detectors. Muons are short lived particles that carry the same charge as electrons, have a high penetrating power and can be detected relatively easy. In practice a test set-up consists of a ‘trigger’ and a device under test. The ‘trigger’ is a detector that gives a signal when a muon passes by, which is a signal to check the result in the device under test. Did the device under test respond to the muon in the expected way?

For the planned upgrades of particle detectors at CERN, for LHC experiments (LHCb, ATLAS, ALICE, CMS), new particle detectors are under development. Some of these new detectors must be able to measure within tens of ps (10e-12 s) precise when a particle was detected.

To facilitate testing these new detectors by using muons we need a trigger set up with a matching precision in timing (order tens of ps). We want to investigate several potentially interesting technologies to develop such a fast trigger. In one scenario the trigger could be based on the use of Cherenkov light. Cherenkov light is generated when a charged particle traverses a medium faster than the speed of light in that medium. This light can be generated in for example plexiglass, which in turn can be mounted on top of a light sensor. In our case the light sensor could be a so called silicon photo multiplier, which is capable of detecting only a few photons and gives a signal within a few hundred ps. Another possible scenario would be to use a so called LGAD (Low Gain Avalanche Diode) to measure the signal that a muon generates as it traverses the sensor.

The Question(s): Which technology should we use for a fast trigger and what is the best timing precision that we can achieve?

This project will involve a lot of 'hands on work' in the lab.

Contact: Martin Fransen and Jory Sonneveld

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

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

Contacts: [Akiba] and [van Beuzekom]

Detector R&D: Simulation of 3D silicon sensors

For the upgrade of the vertex detector of the LHCb experiment novel silicon pixel detectors have to be developed that can register the passing particles with a time precision of tens of picoseconds. Given the harsh radiation environment very close to the LHCb interaction point only a limited number of technologies can be applied. One of the most promising technologies are the so-called 3D sensors whose readout electrodes are pillars that are placed into the sensor perpendicular to the surface; this in contrast to ’standard’ planar silicon sensors where the pixel electrodes are at the surface, similar to the camera in your smartphone. To understand the time response of these 3D sensors, simulations with TCAD software have to be performed and the results will be compared to measured data. These simulations involve the creation/adaptation of the 3D structures of the model, optimising the simulation speed, and analysing the signals as function voltage, track impact point and deposited charge. Hands-on experience with such 3D sensors in the R&D labs at Nikhef is planned within the scope of this project.

Contacts: [van Beuzekom] and [Akiba]

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

The space-based gravitational wave antenna LISA is one of the most challenging space missions ever proposed. ESA plans to launch around 2034 three spacecraft separated by a few million kilometres. This constellation measures tiny variations in the distances between test-masses located in each satellite to detect gravitational waves from sources such as supermassive black holes. LISA is based on laser interferometry, and the three satellites form a giant Michelson interferometer. LISA measures a relative phase shift between one local laser and one distant laser by light interference. The phase shift measurement requires sensitive wavefront sensors. The Nikhef DR&D group fabricated prototype sensors in 2020 together with the Photonics industry and the Dutch institute for space research SRON. Nikhef & SRON are responsible for the Quadrant PhotoReceiver (QPR) system: the sensors, the housing including a complex mount to align the sensors with 10's of nanometer accuracy, various environmental tests at the European Space Research and Technology Centre (ESTEC), and the overall performance of the QPR in the LISA instrument. Currently we are discussing possible sensor improvements for a second fabrication run in 2022, optimizing the mechanics and preparing environmental tests. As a MSc student, you will work on various aspects of the wavefront sensor development: study the performance of the epitaxial stacks of Indium-Gallium-Arsenide, setting up test benches to characterize the sensors and QPR system, performing the actual tests and data analysis, in combination with performance studies and simulations of the LISA instrument.

Contact: Niels van Bakel

FCC: The Next Collider

After the LHC, the next planned large collider at CERN is the proposed 100 kilometer circular collider "FCC". In the first stage of the project, as a high-luminosity electron-positron collider, precision measurements of the Higgs boson are the main goal. One of the channels that will improve by orders of magnitude at this new accelerator is the decay of the Higgs boson to a pair of charm quarks. This project will estimate a projected sensitivity for the coupling of the Higgs boson to second generation quarks, and in particular target the improved reconstruction of the topology of long-lived mesons in the clean environment of a precision e+e- machine.

Contact: Tristan du Pree

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

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

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

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

Contact: Lex Greeven and Niels Tuning

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

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

Contact: Wouter Hulsbergen and Mara Soares

LHCb: Discovering heavy neutrinos in B decays

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

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

Contact: Lera Lukashenko and Wouter Hulsbergen

LHCb: The exotic 4-quark state X(3872) in exclusive production

The nature of the X(3872) is still unknown. Is it a regular charmonium with an unexpected mass, a compact 4-quark state, or a DD molecule? Or a quantum superposition of all that? Either way, finding out will tell us something about how quark organise in hadrons and colour confinement. The project is to measure a very peculiar production mode: pp->Xpp. Only the X is seen in the detector and nothing else. Data from LHCb run 2 will be used and the analysis will build on previous work.

Contact: Patrick Koppenburg

LHCb: Scintillating Fibre tracker software

The installation of the scintillating-fibre tracker in LHCb’s underground cavern was recently completed. This detector uses 10000 km of fibres to track particle trajectories in the LHCb detector when the LHC starts up again later this year. The light emitted by the scintillating fibres when a particle interacts with them is measured using photon multiplier tubes. The studies proposed for this project will focus on software, and could include writing a framework to monitor the detector output, improving the detector simulation or working on the data processing.

Contact: Emmy Gabriel

Neutrinos: Neutrino scattering: the ultimate resolution

Neutrino telescopes like IceCube and KM3NeT aim at detecting neutrinos from cosmic sources. The neutrinos are detected with the best resolution when charged current interactions with nucleons produce a muon, which can be detected with high accuracy (depending on the detector). A crucial ingredient in the ultimate achievable pointing accuracy of neutrino telescopes is the scattering angle between the neutrino and the muon. While published computations have investigated the cross-section of the process in great detail, this important scattering angle has not received much attention. The aim of the project is to compute and characterize the distribution of this angle, and that the ultimate resolution of a neutrino telescope. If successful, the results of this project can lead to publication of interest to the neutrino telescope community.

Depending on your interests, the study could be based on a first-principles calculation (using the deep-inelastic scattering formalism), include state-of-the-art parton distribution functions, and/or exploit existing event-generation software for a more experimental approach.

Contacts: Aart Heijboer

Neutrinos: acoustic detection of ultra-high energy neutrinos

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

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

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

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

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

Contact: Ernst Jan Buis or Ivo van Vulpen

Neutrinos: Oscillation analysis with the first data of KM3NeT

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

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

Neutrinos: the Deep Underground Neutrino Experiment (DUNE)

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

Contact: Paul de Jong

Neutrinos: Searching for Majorana Neutrinos with KamLAND-Zen

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

Cosmic Rays/Neutrinos: Seasonal muon flux variations and the pion/kaon ratio

The KM3NeT ARCA and ORCA detectors, located kilometers deep in the Mediterranean Sea, have neutrinos as primary probes. Muons from cosmic ray interactions reach the detectors in relatively large quantities too. These muons, exploiting the capabilities and location of the detectors allow the study of cosmic rays and their interactions. In this way, questions about their origin, type, propagation can be addressed. In particular these muons are tracers of hadronic interactions at energies inaccessible at particle accelerators.

The muons reaching the depths of the detectors result from decays of mesons, mostly pions and kaons, created in interactions of high-energy cosmic rays with atoms in the upper atmosphere. Seasonal changes of the temperature – and thus density - profile of the atmosphere modulate the balance between the probability for these mesons to decay (producing muons) or to re-interact. Pions and kaons are affected differently, allowing to extract their production ratio by determining how changes in muon rate depend on changes in the effective temperature – an integral over the atmospheric temperature profile weighted by a depth dependent meson production rate.

In this project, the aim is to measure the rate of muons in the detectors and to calculate the effective temperature above the KM3NeT detectors from atmospheric data, both as function of time. The relation between these two can be used to extract the pion to kaon ratio.

Contact: Ronald Bruijn

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

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

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

Contact: Andreas Freise

Theory: Effective Field Theories of Particle Physics from low- to high-energies

Known elementary matter particles exhibit a surprising three-fold structure. The particles belonging to each of these three “generations” seem to display a remarkable pattern of identical properties, yet have vastly different masses. This puzzling pattern is unexplained. Equally unexplained is the bewildering imbalance between matter and anti-matter observed in the universe, despite minimal differences in the properties of particles and anti-particles. These two mystifying phenomena may originate from a deeper, still unknown, fundamental structure characterised by novel types of particles and interactions, whose unveiling would revolutionise our understanding of nature. Until recently, it was widely assumed that matter particles from each of the three generations interact with the same (“universal”) strength. This hypothesis is being challenged by new measurements at the Large Hadron Collider (LHC) at CERN, which hint towards non-universal interactions. If confirmed, these measurements will be the first signs of new particles and interactions in high-energy colliders. These exciting findings indicate the urgent need to explore such phenomena in depth. The ultimate goal of particle physics is uncovering a fundamental theory which allows the coherent interpretation of phenomena taking place at all energy and distance scales. In this project, the students will exploit the Effective Field Theory (EFT) formalism, which allows the theoretical interpretation of particle physics data in terms of new fundamental quantum interactions which relate seemingly disconnected processes. Specifically, the goal is to connect measurements from ATLAS and LHCb among them and to jointly interpret this information with that provided by other experiments, from CMS and Belle-II to very low-energy probes such as the anomalous magnetic moment of the muon or electric dipole moments of the electron and neutron.

This project will be based on theoretical calculations in particle physics, numerical simulations in Python, analysis of existing data from the LHC and other experiments, as well as formal developments in understanding the operator structure of effective field theories. This project accommodates several students, who would work together in developing the main formalism while each of them focuses on a specific sub-project. Depending on the student profile, sub-projects with a strong computational and/or machine learning component are also possible.

Subproject #1: SMEFT & Flavour symmetries. While the power of the Standard Model EFT (named SMEFT) framework is its generality and lack of assumptions, the number of operators is somewhat daunting. A popular way to trim the number of operators is to assume flavour symmetries that relate operators with different quark and lepton flavours. In this project you will investigate the theoretical basis for commonly-used flavour symmetries and what they imply for the connection between high-energy observables involving third-generation particles (top and bottom quarks and tau leptons) and low-energy precision tests involving first- and second-generation particles.

Subproject #2: SMEFT & magnetic moment of the muon. The magnetic moment of the muon appears to differ from the Standard Model expectations by a large amount, well beyond the known experimental and theoretical uncertainties. Recent experiments have only strengthened the significance of this anomaly. In this project, the students will investigate the feasibility of implementing the measurement of the magnetic moment of the muon into a global SMEFT analysis, by exploiting recently provided calculations. Special attention will be devoted to the flavour assumptions required to consistently match this measurement with the LHC data. The SMEFiT analysis framework will be used to connect the g-2 data with high-energy LHC measurements.

References: arXiv:2105.00006, https://arxiv.org/abs/1901.05965 , https://arxiv.org/abs/1906.05296 ,  https://arxiv.org/abs/1908.05588,  https://arxiv.org/abs/1905.05215

Contacts: Juan Rojo, Keri Vos, Jordy de Vries

Theory: High-energy neutrino-nucleon interactions at the Forward Physics Facility

High-energy collisions at the High-Luminosity Large Hadron Collider (HL-LHC) produce a large number of particles along the beam collision axis, outside of the acceptance of existing experiments. The proposed Forward Physics Facility (FPF) to be located several hundred meters from the ATLAS interaction point and shielded by concrete and rock, will host a suite of experiments to probe Standard Model (SM) processes and search for physics beyond the Standard Model (BSM). High statistics neutrino detection will provide valuable data for fundamental topics in perturbative and non-perturbative QCD and in weak interactions. Experiments at the FPF will enable synergies between forward particle production at the LHC and astroparticle physics to be exploited. The FPF has the promising potential to probe our understanding of the strong interactions as well as of proton and nuclear structure, providing access to both the very low-x and the very high-x regions of the colliding protons. The former regime is sensitive to novel QCD production mechanisms, such as BFKL effects and non-linear dynamics, as well as the gluon parton distribution function (PDF) down to x=1e-7, well beyond the coverage of other experiments and providing key inputs for astroparticle physics. In addition, the FPF acts as a neutrino-induced deep-inelastic scattering (DIS) experiment with TeV-scale neutrino beams. The resulting measurements of neutrino DIS structure functions represent a valuable handle on the partonic structure of nucleons and nuclei, particularly their quark flavour separation, that is fully complementary to the charged-lepton DIS measurements expected at the upcoming Electron-Ion Collider (EIC).

In this project, the student(s) will carry out updated predictions for the neutrino fluxes expected at the FPF, assess the precision with which neutrino cross-sections will be measured, and quantify their impact on proton and nuclear structure by means of machine learning tools and state-of-the-art calculations in perturbative Quantum Chromodynamics.

References: arXiv:2109.10905, arXiv:2201.12363 , arXiv:2109.02653

Contacts: Juan Rojo

Theory: Probing the origin of the proton spin with machine learning

At energy-frontier facilities such as the Large Hadron Collider (LHC), scientists study the laws of Nature in their quest for novel phenomena both within and beyond the Standard Model of particle physics. An in-depth understanding of the quark and gluon substructure of protons and heavy nuclei is crucial to address pressing questions from the nature of the Higgs boson to the origin of cosmic neutrinos. The key to address some of these questions is by carrying out an universal analysis of nucleon structure from the simultaneous determination of the momentum and spin distributions of quarks and gluons and their fragmentation into hadrons. This effort requires combining an extensive experimental dataset and cutting-edge theory calculations within a machine learning framework where neural networks parametrise the underlying physical laws while minimizing ad-hoc model assumptions.

In this project, the student(s) will carry out a new global analysis of the spin structure of the proton by means of machine learning tools and state-of-the-art calculations in perturbative Quantum Chromodynamics, and integrate it within the corresponding global NNPDF analyses of unpolarised proton and nuclear structure in the framework of a combined integrated global analysis of non-perturbative QCD.

References: arXiv:2201.12363 , arXiv:2109.02653

Contacts: Juan Rojo

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PREVIOUS PROJECTS! Projects with a 2021 start

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

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

Contact: Panos Christakoglou and Alessandro Grelli and Marco van Leeuwen

ALICE: Searching for the strongest magnetic field in nature

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

Contact: Panos Christakoglou

ALICE: Looking for parity violating effects in strong interactions

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

Contact: Panos Christakoglou

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

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

Contact: Panos Christakoglou and Alessandro Grelli

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

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

Contact: Marco van Leeuwen and Marta Verweij

ALICE: Extreme Rare Probes of the Quark-Gluon Plasma

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

Contact: Marta Verweij and Marco van Leeuwen

ALICE: Jet Quenching with Machine Learning

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

Contact: Marta Verweij and Marco van Leeuwen

ATLAS: Top Spin and EFTs in the Wtb vertex

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

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

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

Contact: Marcel Vreeswijk [2] and Jordy Degens [3]

ATLAS: The Next Generation

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

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

Contact: Tristan du Pree

ATLAS: The Most Energetic Higgs Boson

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

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

Contact: Tristan du Pree

ATLAS: Searching for new particles in very energetic diboson production

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

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

Contact: Flavia de Almeida Dias

ATLAS R&D: Study of LGAD sensors

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

Contact: Hella Snoek

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

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

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

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

Contact: Lex Greeven and Niels Tuning

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

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

Contact: Wouter Hulsbergen and Mara Soares

LHCb: Discovering heavy neutrinos in B decays

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

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

Contact: Lera Lukashenko and Wouter Hulsbergen

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

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

Contact: Patrick Koppenburg

With the Dark Matter group: Fine structure constant

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

Contact: Auke-Pieter Colijn

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

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

Contact: Tina Pollmann and Patrick Decowski

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

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

Contact: Patrick Decowski and Auke Colijn

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

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

Contact: Patrick Decowski and Auke Colijn

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

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

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

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

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

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

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

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

Contacts: Kazu Akiba and Martin van Beuzekom

Detector R&D: Studying fast timing detectors

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

Contact: Hella Snoek or Kazu Akiba

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

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

Contact: Niels van Bakel

Detector R&D: Time tracking Cosmic rays

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

Contacts: Kazu Akiba and Martin van Beuzekom

Neutrinos: Searching for Majorana Neutrinos with KamLAND-Zen

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

Neutrinos: acoustic detection of ultra-high energy neutrinos

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

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

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

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

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

Contact: Ernst Jan Buis or Ivo van Vulpen

Neutrinos: Oscillation analysis with the first data of KM3NeT

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

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

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

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

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

Neutrinos: Dark Matter with KM3NeT-ORCA

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

Contact: Suzan B. du Pree Daan van Eijk

Neutrinos: the Deep Underground Neutrino Experiment (DUNE)

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

Contact: Paul de Jong

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

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

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

Contact: Andreas Freise

Gravitational Waves: Digging away the noise to find the signal

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

Contact: Bas Swinkels and Sarah Caudill

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

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

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

Contact: Marieke Postma

Theory: Higgs inflation

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

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

Contact: Marieke Postma

Theory: Neutrinos, hierarchy problem and cosmology

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

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

Contact: Marieke Postma

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Last year's MSc Projects