Bachelor Projects

Bachelor Projects 2022

Dark Matter

Response of materials to scintillation light from liquid noble gasses

The liquid form of the noble gases argon and xenon is a popular target material for neutrino and dark matter detectors. The scintillation light from noble gases is in the vacuum UV spectral region. Air and many materials used for optical studies are not transparent to these photons. Measurements of the optical properties of detector materials, such as their reflectivity for example, thus have to be performed with dedicated VUV optics and in vacuum. Additionally, to reproduce the conditions in the detectors, the samples must be cooled to cryogenic temperatures. In this BSc project, you will calibrate the photon detectors in an experimental setup designed to study the optical response of materials excited with VUV photons. You will learn about material requirements for rare event search detectors, vacuum instrumentation, vacuum UV optics including monochromators and spectrometers, and single-photon sensors.

Supervisors: T. Pollmann (t.pollmann_at_nikhef.nl)

ATLAS

The Higgs boson - did we miss anything and can we do better?

The Higgs boson is a key element of the Standard Model (SM) of particle physics, however, it can also represent a link between yet unexplored 'new' physics beyond the SM. What is the Higgs boson life-time? How precisely can we measure its mass? Is there an additional heavy Higgs boson? Do other particles, not contained in the SM, couple to the Higgs? All these questions can be studied by measuring Higgs properties using one of the Higgs decay modes to photons, vector bosons, quarks and leptons and comparing them with the (beyond) SM predictions.

As the restart of the Large Hadron Collider (LHC) is imminent, it is essential to develop and test new physics ideas and strategies. The ATLAS open data project will allow students to work on a real analysis digging through the LHC data collected during Run2. Students will go through all the key aspects of a Higgs analysis performed also by ATLAS physicists. They will learn about Higgs boson theory and its simulation, what objects are reconstructed in the ATLAS experiment, how well do we understand them and finally how does this project into our understanding of the Higgs boson and its properties.

The exact focus of the topic is flexible depending on the interest of a student. For instance, a student can delve into how precisely can we determine objects' energy and their positions and see whether we can improve our estimate of the Higgs mass (project 1). Another possibility is to focus on trying to find out whether there is an additional (heavier) Higgs (project 2) in the data and how confident we can be of that. Each of these projects will most likely yield new questions, so feel free to take a tangent and walk into yet unexplored territory and see what the data tells you.

Supervisor: Matouš Vozak (m.vozak_at_nikhef.nl) & Ivo van Vulpen (Ivo.van.Vulpen_at_nikhef.nl)

The Higgs boson life-time

The Higgs particle does not have eternal life. The Standard Model (SM) predicts that it decays into other particles and as these couplings are fixed we can predict its life-time with very high precision. Determining this life-time is a crucial test for the Standard Model. If the Higgs boson life-time is shorter that we expect this could mean that the Higgs boson could decay into non-SM particles. In this project we investigate a) how we can identify Higgs particles in the detector and b) how we plan to use quantum-interference to get a handle on the Higgs boson's life-time.

Supervisor: Wouter Verkerke (verkerke_at_nikhef.nl)

LHCb

Exotic 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, heavier, neutral leptons. In the LHCb group at Nikhef 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 bachelor project will contribute with the optimization of the selection using state-of-the-art tools for the multi-variate analysis.

Contact: Wouter Hulsbergen

Detector R&D

Answering big elementary particle physics questions requires pioneering experiments. The Detector R&D program at Nikhef is aimed at conceptualizing and testing of instrumentation concepts before they are implemented in scientific programs at Nikhef.

Time resolution of monolithic timing detectors

For the upgrade of the vertex detectors of the large LHC experiments like LHCb and ALICE, new silicon pixel detectors will 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 resulting in ultrathin, low-material detectors. In this project you will measure the time resolution of these promising integrated sensors with a laser setup in our laboratory.

Supervisor: Jory Sonneveld -- jory.sonneveld@nikhef.nl

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. Analyses of LHC data rely heavily on simulations of the detector. 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 part of the international ATLAS collaboration and compare different models of radiation damage with measured data and you will contribute to the open source program Allpix Squared that is widely used for simulations in many areas of particle physics.

Supervisor: Jory Sonneveld -- jory.sonneveld@nikhef.nl

Time resolution of a new digital pixel test structure from test beam data

For the upgrade of the ALICE detector, ultrathin picosecond timing integrated sensors are developed. To reduce power consumption, asynchronous readout is implemented in this prototype sensor in a digital pixel test structure. This structure was studied in test beams with an ALPIDE (ALICE PIxel DEtector) telescope at CERN. You will measure the efficiency and time resolution of this new sensor with the latest data from test beams at CERN.

Supervisor: Jory Sonneveld -- jory.sonneveld@nikhef.nl

KM3NeT

The KM3NeT collaboration is constructing a new generation neutrino telescope with a volume of several cubic kilometers (final configuration) in the deep waters of the Mediterranean Sea. With the data, scientists will look for the astrophysical sources of neutrinos such as supernovae, colliding stars or gamma-ray bursts. In the domain of particle physics the properties of neutrinos will be investigated, in particular the unknown neutrino mass hierarchy.

The KM3NeT telescope detects the Cherenkov light emitted by the secondary particles produced in neutrino interactions using an array of thousands of sensitive 3 inch photo-multiplier tubes housed in 17 inch pressure resistant glass spheres, digital-optical-modules (DOMs), together with electronics. The DOMs are oriented along 200-700m long vertical lines, called detection units.

Neutrino oscillation measurements with the first KM3NeT data

The ORCA block of the KM3NeT neutrino telescope is able to measure the oscillations of neutrinos produced in interactions of cosmic rays with the earth atmosphere. Fundamental neutrino properties can be deduced from these oscillations measurements. In this project we will use the first data of ORCA (more than one year with six detection units) to study neutrino oscillations and fit neutrino mixing parameters and mass differences between neutrino mass states. We will study data selection, event reconstruction, and effects of systematic uncertainties on the results.

Supervisors: Brian O'Fearraigh, Ronald Bruijn, Paul de Jong (paul.de.jong at nikhef.nl)

Search for sterile neutrinos with KM3NeT.

A detailed study of neutrino oscillations in the KM3NeT detector is sensitive to the existence of so-called sterile neutrinos: neutrinos that are not part of the Standard Model of particle physics, and have no ordinary interactions with matter. We will use a mixture of data and simulations to estimate KM3NeT sensitivity.

Supervisors: Alba Domi, Paul de Jong

Machine learning for event classification in KM3NeT

The classification of neutrino events recorded in the KM3NeT detector in terms of originating from electron neutrinos, muon neutrinos, or tau neutrinos, is very well suited for machine learning techniques. We will study the performance of a few advanced machine learning techniques on simulated high-energy neutrino events.

Supervisors: Alba Domi, Paul de Jong

Multi-messenger astronomy with neutrinos and radio signals

The main goal of neutrino telescopes, such as ANTARES, KM3NeT and IceCube, is to detect cosmic neutrinos from astrophysical sources. When an interesting neutrino candidate is detected they send out a message to alert the scientific community. Other scientific instruments, like the Murchison Widefield Array (MWA) radio telescope, can then do a follow-up observation, to see if there are other messengers coming from the same source as the neutrinos. In this project you will analyse MWA data that were taken after the reception of neutrino alerts, to search for a radio source that can be associated with a neutrino source.

Supervisor: Mieke Bouwhuis (mieke.bouwhuis at nikhef.nl)

Theory

Symmetries and sterile neutrinos

The fact that neutrinos have masses is problematic for the Standard Model. A plausible solution requires the existence of additional so-called sterile neutrinos. In this project we will study why such neutrinos could exist and describe their mixing with the active neutrinos we have seen in experiments. In particular, we will investigate how large active-sterile mixing can be while accounting for the small neutrino masses and what this tells us about possible lepton number violation.

Supervisor: Jordy de Vries

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.

Methodology and workplan

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. The maximum capacity of this project is 5 students.

Depending on the student profile, sub-projects with a strong computational / machine learning component are also possible.

During the first four weeks of the project, students will learn the required background material on effective field theories, following the guidelines from the supervisors. Afterwards, they will focus on different sub-projects, each covering a different aspect of the same global EFT program.

Required knowledge

Quantum Mechanics 2, Particle Physics 1 (required)

Advanced Quantum Mechanics, Particle Physics 2, Machine Learning (optional)

Available subprojects

Here we list the available subprojects, including the corresponding daily supervisor(s) in each case.

Subproject #1: SMEFT & Flavour symmetries

Daily supervisors: Jordy de Vries (UvA), Keri Vos (Maastricht University), Jaco ter Hoeve (VU), Giacomo Magni (VU)

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. The investigations of this project are connected with Subproject #2.

Subproject #2: SMEFT & magnetic moment of the muon

Daily supervisors: Keri Vos (Maastricht University), Juan Rojo (VU)

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, also at the light of the connection with Subproject #1. The SMEFiT analysis framework will be used to connect the g-2 data with high-energy LHC measurements.

Subproject #3: CP Violation and low-energy precision experiments

Most analyses of LHC data are performed under the assumption that CP symmetry (charge conjugation + parity, essentially the symmetry between particles and anti-particles) is conserved. More recent analyses attempt to also measure possible new sources of CP violation in SMEFT operators in the Higgs and top sector.

Subproject #3a: CP Violation and low-energy precision experiments

Daily supervisors: Jordy de Vries (UvA), Juan Rojo (VU)

Low-energy precision experiments can also set stringent constraints on new mechanisms of CP violation. In this project you will try to combine high- and low-energy data to put CP symmetry to the test.

Subproject #3b: CP Violation and flavour physics experiments

Daily supervisors: Keri Vos (Maastricht University), Juan Rojo (VU)

Besides low-energy precision experiments, also B-meson decays are excellent probes of CP violation. Unlike most low-energy experiments, this allows us to probe CP violation in the third generation. In this project you will link constraints on CP violation at high-energy to those from B meson decays.  

Subproject #4: SMEFT & optimal observables

Daily supervisors: Keri Vos (Maastricht University), Juan Rojo (VU), Tommaso Giani (VU & Nikhef)

In full generality, the number of operators in SMEFT spans a very large parameter space. These parameters are constrained by experimental inputs from ATLAS and CMS, depending on the precise parameters these constraints may be more or less stringent. In order to fully exploit the whole parameters space in SMEFT, it is necessary to devise statistically optimal observables that have a large constraining power. In this project, we will define such observables. This project has a strong computational / machine learning component and may involve simulations based on tools such as MadGraph and Pythia8.

Contacts:

Juan Rojo (VU Amsterdam & Nikhef): j.rojo at vu.nl

Keri Vos (UM & Nikhef): k.vos at maastrichtuniversity.nl

Jordy de Vries (UvA & Nikhef): j.devries4 at uva.nl

Bachelor Projects 2021

Dark Matter

XAMS

The Nikhef dark matter group has a small version of the XENON1T detector in the lab. With this detector which is more than a factor 1000 smaller than the newly built XENON1T detector in Gran Sasso we (i) investigate the properties of xenon as a detector, and (ii) aim to improve the methods we use in the XENON1T experiment to detect dark matter. The principles of operation of this smal detector are identical to its big sibling in Gran Sasso. We are looking for a student interested in dark matter physics, and with a focus on working in the lab (hands-on profile). The student will work with recently upgraded hardware to test a novel concept for UV light detection. The goal of this project will be to do the first measurements with the neutron source and analyze the data. Depending on the progress with the hardware we intend to complete the first measurements with our upgraded setup.

Supervisors: A.P. Colijn (colijn_at_nikhef.nl)

XENONnT reconstruction software

The XENONnT experiment becomes operational during 2021. While the hwardware is finished we keep on developing and perfecting our reconstruction software. For this project we are looking for a student with a keen interest in and talent for writing physics based event reconstruction software (we use python). Specifically we have an idea to improve the localization of events inside the XENONnT for which proto-type software exists. The proto-type software needs to be implemented in the XENONnT reconstruction framework and subsequently it needs to be validated on the first data from the experiment. The final goal of the project is to deliver the reconstruction software to the collaboration that will be used during teh full lifetime of the experiment.

Supervisors: A.P. Colijn (colijn_at_nikhef.nl)

Backgrounds in Radioactive Decay Measurements

At Nikhef, the XENON group has a working setup, continuously monitoring the radioactive decay of Cobalt-60, Caesium-137 and Titanium-44. This beautiful setup is however not shielded perfectly; it is still vulnerable to background radioactivity. Our current way of working around this background radiation is to subtract it from our waveforms. You as a BSc student could help us hands-on and with analyses: together, we can disassemble the setup, measure background spectra and implement this in the data analysis. You can use all the data to validate the lifetime of our isotopes!

Supervisors: A.P. Colijn (colijn_at_nikhef.nl)

Detection of scintillation light from liquid noble gasses

The liquid form of the noble gases argon and xenon is a popular target material for neutrino and dark matter detectors. The scintillation light from noble gases is in the vacuum UV spectral region. Air and many materials used for optics studies are not transparent to these photons. Measurements of the optical properties of detector materials, such as their reflectivity for example, thus have to be performed with dedicated VUV optics and in vacuum. Additionally, to reproduce the conditions in the detectors, the samples must be cooled to cryogenic temperatures. In this BSc project, you will design, using professional hardware design software, a vacuum chamber to hold the detector materials whose optical properties are to be investigated, as well as the cooling system and photon detectors. You will learn about material requirements for rare event search detectors, vacuum instrumentation, vacuum UV optics including monochromators and spectrometers, and single-photon sensors.

Supervisors: T. Pollmann (t.pollmann_at_nikhef.nl)

Detector R&D

Characterization of the new ultrathin ALPIDE monolithic active pixel sensor

At the Large Hadron Collider at CERN, major upgrades of experiments take place in the long shutdown years where particle collisions are paused. The ALICE inner tracking system (ITS) 2, the part of the ALICE experiment closest to the beam pipe, is currently being installed at CERN. This detector makes use of ultra-lightweight monolithic active pixel sensors, the first to use this technology at particle colliders after the STAR experiment at RHIC in Brookhaven. These very thin pixel detectors have a low power consumption, result in very little material in the detector, and still have optimal timing and resolution -- and are a promising technology for future experiments. To characterize the performance of these sensors, you will learn to set up experiments, carry out measurements, and analyze data using various instruments available in the detector R&D lab at Nikhef. This could lead to novel insights of monolithic active pixel sensors. It is also possible to do measurements from home using data from the first test beams with bent (yes, with a curvature!) ALPIDE sensors. You will work in an international, stimulating research environment in the detector R&D group at Nikhef at the forefront of silicon detector technologies for high energy physics. Contact: Jory Sonneveld

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. If time and Covid regulations permit, gaining some hands-on experience with such 3D sensors in the R&D labs at Nikhef is possible. Contacts: Martin van Beuzekom Kevin Heijhoff

Theory

Standard Model Effective Field Theory analysis of Z+dijet production

The goal of this project is to study the effect of higher dimensional operators from the Standard Model Effective Field Theory in Z-boson production measured at LHC. The ATLAS collaboration has just reported in 2020 the measurement of Z production alongside with a pair of jets, based on the full Run II luminosity. In this project we aim to study the effect of dimension six SMEFT operators on the signal (EW-induced) and/or background (QCD-induced), finding which is the kinematic variable that maximises the possible effect of beyond the SM operators and thus may provide the best constraint on New Physics. The outcome of this project may be the first step of the inclusion of Vector production in a global SMEFT fit.

References: https://arxiv.org/pdf/2006.15458.pdf, https://www.hepdata.net/record/ins1803608

Supervisor: J. Rojo (j.rojo_at_vu.nl)

Maximum precision on new physics through information theory

One way to look for physics beyond the standard model is through the framework of effective field theory. In this framework, deviations from the standard model are described by a set of continuous parameters. Finding constraints on these parameters might point to the discovery of new physics. With the large number of LHC experiments we currently face, we want to be able to quantify the maximum knowledge that (future) experiments can provide on new physics parameters. In this project, the student will study and quantify the maximum information that is contained in particle physics experiments through information theory. The central object of study will be the Fisher information matrix. The idea is to work with a simple toy experiment that describes Higgs physics and compute its associated Fisher information matrix to quantify the optimal bounds on new physics. The project will start with studying central objects from statistics and information theory. Later, we will apply these to open problems in particle physics.

Reference: https://arxiv.org/pdf/1612.05261.pdf

Supervisor: J. Rojo (j.rojo_at_vu.nl)

Seesaw mechanism and neutrino mass

Many unsolved questions in particle physics are related to the nature of the neutrino and its mass generation. The goal of this theoretical project is to understand and review one of the possible candidate theories that describe how neutrinos mix and get massive, namely the Seesaw mechanism. Among the many possible Seesaw mechanisms that can generate new phenomenology including lepton number non-conservation, the student will focus on one minimal model to understand the key processes that are currently used to probe the validity of the given theory.

References: https://cds.cern.ch/record/408119/files/9911364.pdf, https://arxiv.org/pdf/1711.02180.pdf

Supervisor: J. Rojo (j.rojo_at_vu.nl)

Mixing of sterile neutrinos

Neutrino oscillation experiments demonstrate that neutrinos are massive particles. However, the mass mechanism of neutrinos is unknown. A minimal solution requires the existence of so-called sterile neutrinos: neutrinos that are even more elusive than ordinary neutrinos. We will investigate how to parametrize the matrix that describes the mixing between ordinary and sterile neutrinos. We will then use this to calculate how sterile neutrinos induce rare nuclear decays and determine the sensitivity of ongoing experiments to observe sterile neutrinos.

Supervisor: Jordy de Vries (devries.jordy at gmail.com)

KM3NeT

The KM3NeT collaboration is constructing a new generation neutrino telescope with a volume of several cubic kilometers (final configuration) in the deep waters of the Mediterranean Sea. With the data, scientists will look for the astrophysical sources of neutrinos such as supernovae, colliding stars or gamma-ray bursts. In the domain of particle physics the properties of neutrinos will be investigated, in particular the unknown neutrino mass hierarchy.

The KM3NeT telescope detects the Cherenkov light emitted by the secondary particles produced in neutrino interactions using an array of thousands of sensitive 3 inch photo-multiplier tubes housed in 17 inch pressure resistant glass spheres, digital-optical-modules (DOMs), together with electronics. The DOMs are oriented along 700m long vertical lines, called detection units.

Data analysis of the first deployed KM3NeT detection lines

First detection lines of the KM3NeT neutrino telescope have been deployed in the Mediterranean Sea, and a first data set is available. The lines consist of light-sensitive detectors that record the time of arrival of photons produced by relativistic particles in the deep sea, and their number. In this project we will study the first data to separate various components: photons from potassium decay, bioluminesence, sparks in the photomultipliers, downgoing muons from cosmic rays, and first neutrinos.

Supervisors: Ronald Bruijn, Paul de Jong and Dorothea Samtleben (paul.de.jong at nikhef.nl)

Neutrino oscillation measurements with the KM3NeT neutrino telescope

The ORCA block of the KM3NeT neutrino telescope currently under construction will be able to measure the oscillations of neutrinos produced in interactions of cosmic rays with the earth atmosphere. Fundamental neutrino properties can be deduced from these oscillations measurements, in particular the so-called mass hierarchy of neutrinos. In this project we will simulate the ORCA measurements of neutrino oscillations, and study the dependence of the sensitivity on experimental uncertainties, such as energy resolution and neutrino flavour identification, and theoretical uncertainties, such as the atmospheric neutrino flux and neutrino cross sections. The results will help ORCA to identify the main sources of uncertainty, and therefore to actively try to reduce these and improve the final measurement.

Supervisors: Ronald Bruijn, Paul de Jong (paul.de.jong at nikhef.nl)

Performance Studies of ORCA for Dark Matter Detection

The interactions of neutrinos in KM3NeT-ORCA give different signatures which are categorised as track and shower events. This project involves the studies of muon, electron and tau neutrino interactions for the reconstruction performance of ORCA. Efficient reconstruction of such signals is important for Dark Matter searches in the low-mass regime. We will work on understanding the detector performance, e.g. effective acceptance, energy and angular resolution, with different configurations of the detector setup. The result of this study will be very useful to improve the sensitivity of the experiment for Dark Matter detection and its possible location. The student will have the opportunity to work closely with KM3NeT members at Nikhef and gain skills of analyzing data.

Supervisors: Suzan Basegmez du Pree, Aart Heijboer (s.basegmez.du.pree at nikhef.nl)

Study of Optical Properties of Sea Water using Hit Coincidences in MC Data

Data from the KM3NeT detector is coming from so-called Digital Optical Modules (DOMs) that are attached to long vertical ropes, which are anchored to the bottom of the Mediterranean Sea at depths down to 3.5 km. There are 18 DOMs in one Detection Unit (i.e. one line), vertically spaced along the length of the DU. Ultimately, hundreds of KM3NeT DUs will be deployed. Every DOM contains 31 photomultiplier tubes (PMTs). A so-called L1 hit is defined as a certain number of single PMT hits in one DOM in a certain time window.

By studying coincidences of L1 hits between neighbouring DOMs, for various Monte Carlo (MC) data sets with different sea water optical properties such as scattering and absorption coefficients, in this project we try to figure out if and how well we can quantify optical sea water properties by studying L1 hit coincidences in real KM3NeT data.

Supervisor: Daan van Eijk (dveijk at nikhef.nl)

Determination of Inter-DOM Distances using Hit Coincidences in KM3NeT Data

Data from the KM3NeT detector is coming from so-called Digital Optical Modules (DOMs) that are attached to long vertical ropes, which are anchored to the bottom of the Mediterranean Sea at depths down to 3.5 km. There are 18 DOMs in one Detection Unit (i.e. one line), vertically spaced along the length of the DU. Ultimately, hundreds of KM3NeT DUs will be deployed. Every DOM contains 31 photomultiplier tubes (PMTs). A so-called L1 hit is defined as a certain number of single PMT hits in one DOM in a certain time window.

The number of L1 hit coincidences from atmospheric muons between neighbouring DOMs on a DU is expected to decrease exponentially. By fitting the observed number of L1 hit coincidences between neighbouring DOMs in real data to the expected exponential decay, in this project we study how accurately we can determine the distances between DOMs on a single DU. In addition, we try to determine the distances between DUs by looking for L1 hit coincidences between DOMs on neighbouring DUs.

Supervisor: Daan van Eijk (dveijk at nikhef.nl)

ATLAS

The Higgs boson life-time

The Higgs particle does not have eternal life. The Standard Model (SM) predicts that it decays into other particles and as these couplings are fixed we can predict its life-time with very high precision. Determining this life-time is a crucial test for the Standard Model. If the Higgs boson life-time is shorter that we expect this could mean that the Higgs boson could decay into non-SM particles. In this project we investigate a) how we can identify Higgs particles in the detector and b) how we plan to use quantum-interference to get a handle on the Higgs boson's life-time.

Supervisor: Wouter Verkerke (verkerke_at_nikhef.nl)

The Higgs boson decaying to photons

One of the main channels used to analyse the properties of the Higgs boson is when the Higgs boson decays into two photons. The crucial building block in this analysis is our ability to reconstruct the energy and the direction of the photons in the ATLAS detector and in this project we will revisit the photon reconstruction. We will start by studying simulations and learning about photon reconstruction in general. Then our goal is to determine the energy and position resolution of photons in the ATLAS detector and see if we can exploit our knowledge on the photon resolution to get an (improved) estimate of the Higgs boson mass. For the analysis we will use the real data from the LHC - the ATLAS open data project.

Supervisor: Ashley McDougall and Ivo van Vulpen (Ivo.van.Vulpen_at_nikhef.nl)

LHCb (1)

One of the most fascinating mysteries in physics today is: how is it possible that universe is filled with matter? If the Big Bang produced equal amounts of matter and antimatter, we still do not understand the mechanism that lead to the excess of matter over antimatter that we observe today.

One interesting feature of some particles is that they can transform themselves into their antiparticles, then back to particle, and so forth, in an oscillatory way until they finally decay. In particular, beauty mesons (B) can oscillate into their antiparticle (B ̄). The parameters of this oscillation, such as amplitude, frequency and phase, are calculable mathematically: predictions for it are available in the standard model (SM) of particle physics. But the oscillations according to the SM alone would not lead to the imbalance of matter in the universe – we still need to find a new type of physics that may be able to explain it.

In this context, it is very important to measure B oscillations in the laboratory, and compare these observations with the expectations from the SM. Are the experimental data in good agreement with the SM, as we expect? If the aswer is not, i.e. if there are features of the oscillation that we do not understand well, then we may be observing “new physics”. In other words, the data may reveal a new mechanism that generates a different matter-antimatter balance than predicted by the SM, that may potentially solve the puzzle.

The LHCb experiment at CERN is dedicated to such studies: LHCb detectors are placed in a region along the LHC collider beamline, where a large number of B mesons are produced, arising from the proton-proton collision data from the LHC collider. Looking at the LHCb data we can obtain large samples of B mesons, and observe their oscillations. In this project we will learn how to select a sample of B mesons out of the data taken with the LHCb detector, measure the parameters that govern their oscillation and compare them with the SM.

For more information, please contact Mara Soares (msoares_at_nikhef.nl).

Bachelor Projects 2020

Dark Matter

XAMS

The Nikhef dark matter group has a small version of the XENON1T detector in the lab. With this detector which is more than a factor 1000 smaller than the newly built XENON1T detector in Gran Sasso we (i) investigate the properties of xenon as a detector, and (ii) aim to improve the methods we use in the XENON1T experiment to detect dark matter. The principles of operation of this smal detector are identical to its big sibling in Gran Sasso. We are looking for a student interested in dark matter physics, and with a focus on working in the lab (hands-on profile). The student will work with the new AmBe neutron source and liquid scintillatorneutron detector we have acquired for the project. With such a source we can generate signals in our lab setup that ar identical to the signals we expect from real dark matter interactions in xenon. The goal of this project will be to do the first measurements with the neutron source and analyze the data. Depending on the progress with the hardware we intend to complement the measurements with Monte Carlo study of neutron transport in xenon. Supervisors: A.P. Colijn (colijn_at_nikhef.nl)

Backgrounds in Radioactive Decay Measurements

At Nikhef, the XENON group has a working setup, continuously monitoring the radioactive decay of Cobalt-60, Caesium-137 and Titanium-44. This beautiful setup is however not shielded perfectly; it is still vulnerable to background radioactivity. Our current way of working around this background radiation is to subtract it from our waveforms. You as a BSc student could help us hands-on and with analyses: together, we can disassemble the setup, measure background spectra and implement this in the data analysis. You can use all the data to validate the lifetime of our isotopes!

Supervisors: A.P. Colijn (colijn_at_nikhef.nl)

ATLAS

Project ATLAS-ITk

Voor de ATLAS upgrade van de binneste detector, de tracking detector ITk zal op Nikhef een groot onderdeel worden gebouwd: de End-Cap met een doorsnede van 2meter en 1.6meter lang. De silicium detectoren worden gekoeld met CO2, waarvoor een testopstelling ontwikkeld en doorgerekend moet worden. Hier ligt een flinke uitdaging voor een bachelorstudent die kennis heeft van thermodynamica en die affiniteit heeft met technische toepassingen. De berekeningen maken gebruik van een software pakket COBRA waar eventueel nog verfijningen in zijn aan te brengen. Het werk zal onder begeleiding plaatsvinden van ir Jesse van Dongen en dr Marcel Vreeswijk. (h73_at_nikhef.nl)

The Most Energetic Higgs Boson

A common approach to search for physics beyond the standard model is by searching for the direct production of new particles. Alternatively, indirect quantum effects on the production of known particles -such as the Higgs Boson- could reveal the first cracks in the theory. Processes with high energy transfer are of particular potential since possible deviations are expected to increase with the square of the involved energy scale. Using the entire data-set collected by the ATLAS experiment at CERN during the four years of the LHC’s Run 2, a proof-of-principle analysis, targeting transverse momenta of the above 400 GeV, has been developed by Nikhef researchers. The first results of this Higgs boson study are expected to be published this year and this project aims to develop refinements of the analysis techniques. We will investigate the usage of sophisticated machine learning tools such as artificial neural networks, the search for new variables that can help discriminating the signal from its background, revisiting the analysis categorisation and improving the reconstruction techniques at these extreme momenta. Supervisors: Brian Moser and Tristan du Pree (tdupree_at_nikhef.nl)

Higgs: 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 has been developed by Nikhef researchers 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 a new statistical combination with various independent searches, which could significantly improve the discovery potential. Supervisors: Marko Stamenkovic and Tristan du Pree (tdupree_at_nikhef.nl)

Higgs interferentie

In 2012 hebben het ATLAS en het CMS experiment het Higgs deeltje gevonden. Inmiddels zijn we het Higgs boson aan het bestuderen, hoe gedraagt het zich precies, bestaan er meer soorten Higgs bosonen of is er echt maar eentje van? In dit project leer je hoe we een Higgs boson kunnen herkennen in de detector en gaan we kijken naar hoe de signalen veranderen als er meer Higgs bosonen bestaan of misschien wel andere exotische nieuwe deeltjes. Dit doen we door gebruik te maken van quantum interferentie wat plaats vindt tussen het Higgs boson en achtergrondprocessen. Hoe dit precies werkt leer je in het project. Supervisor: Hella Snoek (h.snoek_at_nikhef.nl)

B-Physics - LHCb

Time dependent CP violation

The LHCb experiment studies CP violation withB-meson decays. The project focusses on the measurement of the unitarity angle gamma using decays of the Bs mesons to Ds K. Supervisors: Sevda Esen & Michele Veronesi

Machine learning

Machine learning has proven to be an indispensable tool in the selection of interesting events in high energy physics. Such technologies will become increasingly important as detector upgrades are introduced and data rates increase by orders of magnitude. HEPDrone is a toolkit to enable the creation of a drone classifier from any machine learning classifier, such that different classifiers may be standardised into a single form and executed in parallel. A detailed evaluation of the performance of different drone models in the real production environment of LHCb will give the collaboration a complete idea of not only the advantages of the drone model, but also the limits of drone complexity given the available computing resources. Requirements: Advanced python and Advanced C++ Supervisor: Sean Benson

LHCb simulations of physics beyond the Standard Model

This project is of relatively theoretical and computing nature and performs simulation studies for physics beyond the Standard Model in the context of long lived particles. It is related to test the sensitivity of the LHCb experiment to detect specific signals of physics beyond the Standard Model. supervisor: Carlos Vazquez Sierra

Detector R&D

Fast timing detectoren

Op dit moment maken we veel gebruik van silicon detectoren in onze deeltjes experimenten. Deze zijn gevoelig voor geladen deeltjes en zijn bij uitstek geschikt om de paden vast te leggen die de deeltjes maken die in de botsingen worden gemaakt. Bijvoorbeeld in de Atlas en LHCb experimenten worden tientallen tot honderden deeltjes gemaakt bij elk botsingsgebeurtenis (event) die met 40MHz plaatsvinden. Voor toekomstige deeltjesdetectoren willen we niet alleen het traject vastleggen maar ook met grote precisie een tijdsmeting toevoegen. We hebben hiervoor dus nieuwe detectoren nodig die behalve met een hele hoge snelheid en efficientie de posities van de langsvliegende deeltjes kunnen vastleggen, maar hier ook een zeer nauwkeurige tijdsmeting (in orde van picosecondes) aan kunnen toevoegen. We hebben met verschillende detectoren metingen gedaan, in testbundels op CERN, maar ook in het lab op Nikhef kunnen we metingen doen. In dit project ga je samen met het fast-timing detectoren team op het Nikhef metingen verrichten en de resultaten hiervan bekijken. Contact: Hella Snoek (h.snoek@nikhef.nl)

Muon tomography

In this project we are not looking for where cosmic rays come from. We are looking for what we can use them for instead. The muons in cosmic rays can be used to ‘probe’ massive objects. Muons are short lived particles that carry the same charge as electrons, have a high penetrating power and can be detected relatively easy. It is possible to reconstruct a density distribution within an object by measuring muon scattering and absorption. In this context the objects may be freight containers, buildings, melting furnaces, etc…

Systems that scan objects through the use of muons are often large (objects often need to be enclosed by the system) and complex. The question we want to answer is: Can we develop a smaller, simpler and cheaper system for muon tomography?

A method to detect muons is by using a material that scintillates (emits light) when hit by an ionising particle. When this light emission is prompt after the passage of the muon, timing information of the light can be used to reconstruct the path of the muon. In this experiment we make a muon tracker based on two sheets of scintillating material and photo multiplier tubes (PMTs). Photo multiplier tubes are fast responding and very sensitive light detectors (capable of detecting single photons).

The big question is: How well does this system perform?

Currently a set-up is being build. You have a lot of freedom to choose a focus in this project (theory, simulation, hardware, or a combination of those).

Supervisor: Martin Fransen (martinfr-at-nikhef.nl)

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.

Some themes that students can work on:

- Optimising methods to acquire spectral X-ray images.

- Determining how much existing applications benefit from spectral X-ray imaging and looking for potential new applications.

- Characterising, calibrating, optimising X-ray imaging detector systems.

Supervisor: Martin Fransen (martinfr-at-nikhef.nl)

Holographic emitter

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 is 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 that lacks any 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?

The aspects of a holographic image we are interested in are:

- Noise

- Contrast

- Suppression of under sampling artefacts

- Resolution

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

Supervisor: Martin Fransen (martinfr-at-nikhef.nl)

KM3NeT

The KM3NeT collaboration is constructing a new generation neutrino telescope with a volume of several cubic kilometers (final configuration) in the deep waters of the Mediterranean Sea. With the data, scientists will look for the astrophysical sources of neutrinos such as supernovae, colliding stars or gamma-ray bursts. In the domain of particle physics the properties of neutrinos will be investigated, in particular the unknown neutrino mass hierarchy.

The KM3NeT telescope detects the Cherenkov light emitted by the secondary particles produced in neutrino interactions using an array of thousands of sensitive 3 inch photo-multiplier tubes housed in 17 inch pressure resistant glass spheres, digital-optical-modules (DOMs), together with electronics. The DOMs are oriented along 700m long vertical lines, called detection units.

Data analysis of the first deployed KM3NeT detection lines

First detection lines of the KM3NeT neutrino telescope have been deployed in the Mediterranean Sea, and a first data set is available. The lines consist of light-sensitive detectors that record the time of arrival of photons produced by relativistic particles in the deep sea, and their number. In this project we will study the first data to separate various components: photons from potassium decay, bioluminesence, sparks in the photomultipliers, downgoing muons from cosmic rays, and perhaps first neutrinos.

Supervisors: Ronald Bruijn, Paul de Jong and Dorothea Samtleben

Neutrino oscillation measurements with the KM3NeT neutrino telescope

The ORCA block of the KM3NeT neutrino telescope currently under construction will be able to measure the oscillations of neutrinos produced in interactions of cosmic rays with the earth atmosphere. Fundamental neutrino properties can be deduced from these oscillations measurements, in particular the so-called mass hierarchy of neutrinos. In this project we will simulate the ORCA measurements of neutrino oscillations, and study the dependence of the sensitivity on experimental uncertainties, such as energy resolution and neutrino flavour identification, and theoretical uncertainties, such as the atmospheric neutrino flux and neutrino cross sections. The results will help ORCA to identify the main sources of uncertainty, and therefore to actively try to reduce these and improve the final measurement.

Supervisors: Ronald Bruijn, Paul de Jong and Dorothea Samtleben

Performance Studies of ORCA for Dark Matter Detection

The interactions of neutrinos in KM3NeT-ORCA give different signatures which are categorised as track and shower events. This project involves the studies of muon, electron and tau neutrino interactions for the reconstruction performance of ORCA. Efficient reconstruction of such signals is important for Dark Matter searches in the low-mass regime. We will work on understanding the detector performance, e.g. effective acceptance, energy and angular resolution, with different configurations of the detector setup. The result of this study will be very useful to improve the sensitivity of the experiment for Dark Matter detection and its possible location. The student will have the opportunity to work closely with KM3NeT members at Nikhef and gain skills of analyzing data.

Supervisors: Suzan Basegmez du Pree, Aart Heijboer

A search for periodic sources in Antares data

The Antares deep-sea neutrino telescope has been operated for more then ten years. A search for periodic sources is proposed by applying a fast Fourier transformation (FFT) analysis on the available low-level data. This search will be combined with a (literature) study of pulsars which are thought to emit neutrinos.

Supervisor: Maarten de Jong

Study of Optical Properties of Sea Water using Hit Coincidences in MC Data

Data from the KM3NeT detector is coming from so-called Digital Optical Modules (DOMs) that are attached to long vertical ropes, which are anchored to the bottom of the Mediterranean Sea at depths down to 3.5 km. There are 18 DOMs in one Detection Unit (i.e. one line), vertically spaced along the length of the DU. Ultimately, hundreds of KM3NeT DUs will be deployed. Every DOM contains 31 photomultiplier tubes (PMTs). A so-called L1 hit is defined as a certain number of single PMT hits in one DOM in a certain time window.

By studying coincidences of L1 hits between neighbouring DOMs, for various Monte Carlo (MC) data sets with different sea water optical properties such as scattering and absorption coefficients, in this project we try to figure out if and how well we can quantify optical sea water properties by studying L1 hit coincidences in real KM3NeT data.

Supervisor: Daan van Eijk

Determination of Inter-DOM Distances using Hit Coincidences in KM3NeT Data

Data from the KM3NeT detector is coming from so-called Digital Optical Modules (DOMs) that are attached to long vertical ropes, which are anchored to the bottom of the Mediterranean Sea at depths down to 3.5 km. There are 18 DOMs in one Detection Unit (i.e. one line), vertically spaced along the length of the DU. Ultimately, hundreds of KM3NeT DUs will be deployed. Every DOM contains 31 photomultiplier tubes (PMTs). A so-called L1 hit is defined as a certain number of single PMT hits in one DOM in a certain time window.

The number of L1 hit coincidences from atmospheric muons between neighbouring DOMs on a DU is expected to decrease exponentially. By fitting the observed number of L1 hit coincidences between neighbouring DOMs in real data to the expected exponential decay, in this project we study how accurately we can determine the distances between DOMs on a single DU. In addition, we try to determine the distances between DUs by looking for L1 hit coincidences between DOMs on neighbouring DUs.

Supervisor: Daan van Eijk

VIRGO

The Advanced LIGO and Advanced Virgo interferometers have recently observed gravitational waves from binary neutron star mergers. Prior to merger, as two neutron stars spiral towards each other, the tidal field of one star will cause a deformation in the other. These deformations affect the orbital motion, which in turn gets imprinted onto the gravitational wave signal. This way we can find out how deformable a neutron star is in the first place, which will yield information about the interior of neutron stars; the latter is the main open problem in nuclear astrophysics.

To succeed in this, good models are needed for the gravitational waveforms. The best model currently available which can be generated sufficiently fast on a computer to be useful in data analysis, contains a state-of-the art description of tidal effects, but not neutron star spins. It is generally assumed that neutron stars are slowly spinning, but it needs to be determined how measurements of tides would be affected by the absence of spins in our analyses.

In practice, the project will consist of learning how to use pre-existing gravitational wave data analysis tools, setting up simulations based on them, and interpreting the results.

The VIRGO collaboration operates the advanced VIRGO gravitational waves detector in Italy, and forms together with the LIGO collaboration a consortium that analyzes the data from both VIRGO and LIGO. For projects in the Nikhef VIRGO group, please contact Frank Linde (frank.linde_at_nikhef.nl) or Chris van den Broeck (vdbroeck_at_nikhef.nl)

Bachelor Projects 2017

Extreme Astronomy – Preparing for CTA, the Next-Generation Gamma-Ray Observatory

The Cherenkov Telescope Array (CTA) is a planned facility for measuring gamma rays from space covering more than four orders of magnitude in energy, up to energies exceeding 100 TeV. CTA employs the imaging atmospheric Cherenkov technique to measure properties of cosmic gamma rays. This technique is based on measuring Cherenkov light emitted during the development of a gamma-ray air shower. CTA will be built at two experimental sites, one in the Northern, one in the Southern hemisphere, and will consist of up to 100 telescopes. It represents a major leap forward in sensitivity and precision for gamma-ray astronomy, and will allow us to explore very-high-energy processes of the extreme Universe at an unprecedented level.

Two projects for students are available at the CTA group of UvA in the field of optical and photonic R&D contributing to the starting phase of CTA. For the first project the student will conduct measurements to characterise novel kinds of single-photon detectors, referred to as silicon photomultipliers, and evaluate different types of these sensors for their use for CTA. For the second project the student will develop and test an imaging system making use of a liquid crystal display. This flexible light source will be able to mimic images from different light sources of the night sky as seen by cameras of CTA, for instance gamma-ray air showers or stars, and will be used for camera tests and calibration.

Supervisors: David Berge, Maurice Stephan (postdoc)

Dark Matter

Neutrinoless double beta decay sensitivity study in future dark matter detectors

The discovery of neutrino oscillation (Nobel Physics 2015) means that neutrinos have mass. We already know that their masses are tiny, more than one million times smaller than the next-lightest particle in the standard model, the electron. This raises the question if the mass-generation mechanism is the same for neutrinos as it is for the other subatomic particles. In particular, since neutrinos are electrically neutral, they could be their own anti-particles - we call these types of particles Majorana. The only practical way to discover if neutrinos are Majorana is through the search of an extremely rare radioactive decay called neutrinoless double beta decay (0n2b). A few isotopes are candidates for this process, among them Xe-136. The natural abundance of Xe-136 in natural xenon is about 9%, and this gives the opportunity to look for a 0n2b signal in xenon-based dark matter detectors like XENON1T and the future XENONnT and DARWIN detectors.

We are looking for a student interested in doing a sensitivity study for 0n2b in XENONnT and the DARWIN experiments. The first goal will be to understand the physics addressed in neutrinoless double beta decay. Then the student will inventory possible backgrounds for the signal, use a (controversial) claim of a 0n2b signal as a benchmark and finally obtain the sensitivity of these future detectors. The work will involve simulations and analysis, building on an existing framework developed in our group.

Supervisors: M.P. Decowski & A. Tiseni

Shaking Dark Matter detectors

Our XENON1T detector is built in the lab underneath the Gran Sasso mountains in central Italy. The lab is very well suited for low-background experiments due to the 1.5km of rock overburden. However, as you may know, cental Italy has been plagued by earthqaukes over the past decade, with the most recentones occurring in January 2017. We need a BSc student to investigate the details of such earthquakes in our underground lab. What are the magnitdues by which stuff is moving underground? What are the accelerations? What is the potential effect on our experimental setup? What would ahppen if an earthquake happens much closer to our lab? Furthermore we are interested to find out whether Earthquakes can be predicted. Some papers claim that before an earthquake the radon emanating from rock increases. In our lab we measure the radon concentration as a function of time: can you find a correlation between the measurements and recent earthquakes?

If you are interested in finding out more about earthquakes, please contact M.P. Decowski or A.P. Colijn

XAMS - a baby dark matter detector

The Nikhef dark matter group has a small version of the XENON1T detector in the lab. With this detector which is more than a factor 1000 smaller than the newly built XENON1T detector in Gran Sasso we (i) investigate the properties of xenon as a detector, and (ii) aim to improve the methods we use in the XENON1T experiment to detect dark matter. The principles of operation of this smal detector are identical to its big sibling in Gran Sasso.

We are looking for a student interested in dark matter physics, and with a focus on working in the lab (hands-on profile). The student will work with the new AmBe neutron source we have acquired before the start of the project. With such a source we can generate signals in our lab setup that ar identical to the signals we expect from real dark matter interactions in xenon. The goal of this project will be to do the first measurements with the neutron source and analyze the data. Depending on the progress with the hardware we intend to complement the measurements with Monte Carlo study of neutron transport in xenon.

Supervisors: A.P. Colijn & E. Hogenbirk

Radon is bad for Dark Matter

Radon is the dominant background for xenon based dark matter detectors, like the XENON1T experiment. In our lab at Nikhef we are investigating ways to reduce or eliminate the effect of radon on our sensitivity. For our lab setup XAMS we have designed and constructed a radon detector, that can be used in xenon systems at high-pressure. This completely new detector is now waiting for a BSc student to fully chracterize and use it. During this project you will first study the effect that radon contaminations have on dark matter detectors, then you will start working to understand our new radon detector in detail. You will learn howto use a radioactive source to calibrate the detector: this is something which is not easy and has not been done before in our lab. If you manage to succesfully calibrate the detector, we then want to incorporate it into our lab xenon system at Nikhef and maybe at some later stage in the real XENON1T detector!

The profile of the student to work on this project is broad. I expect a good theoretical knowledge in order to quickly get upto speed with understanding dark mater detectors, and in addition I need 'lab-creativity' in order to develop methods for calibrating the new detector. If a good method is developed, it will be used for many years by the Nikhef dark matter group and beyond.

Supervisors: A.P. Colijn & E. Hogenbirk

ATLAS

ATLAS (1): Searching for new physics with the Higgs and W bosons

The strength of the Higgs interactions with electroweak bosons are precisely defined in the Standard Model. Therefore they are sensitive probes of the mechanism of electroweak symmetry breaking and enable searches for new physics beyond the SM. With the data collected by the ATLAS experiment in years 2015-2016 we plan to measure separately the Higgs coupling to longitudinally and transversely polarised W bosons in a process of weak boson fusion. To maximise experimental sensitivity we are developing techniques to separate the signal from background processes. You will take part in investigating possible improvements from reconstructing events in reference frames boosted with respect to the detector. During the project you will learn modern experimental analysis techniques. This project is a part of Vector Boson Scattering Coordination and Action Network (VBSCan) which connects researchers studying this and related topics worldwide.

Supervisors: Pamela Ferrari, Magdalena Slawinska, Bob van Eijk

ATLAS (2): Dark-matter-motivated searches for supersymmetric particles at the LHC

Supersymmetry, a symmetry between fermions and bosons in particle physics, may provide a particle that could be the dark matter in the universe. The observation of an excess of gamma rays originating from the centre of our galaxy could be explained in a model where supersymmetric dark matter particles annihilate each other in the galactic centre, leading to gamma rays.

Given the model parameters, it should also be possible to produce such particles at the LHC, at CERN in Geneva. But it is not so easy to observe them: the signal is small, and the noise (background) is large. In this project, we will use simulations of signal and background to optimize experimental searches for such particles with the ATLAS detector, apply them to the data collected in 2015, and prepare for the new data in 2016 and later.Where possible, we will explore new machine learning techniques.

Supervisors: Paul de Jong, Broos Vermeulen

ATLAS (3): Simulations / Quality tests for the ATLAS High-Luminosity LHC Upgrade

One of the key sub-systems of the ATLAS experiment at the Large Hadron Collider (LHC) is the Inner Detector (ID), designed to provide excellent charged particles momentum and vertex resolution measurements.

At Phase-2 of the LHC run, in ~2025, the operating luminosity of the collider will be increased significantly. This will imply an upgrade of all ATLAS subsystems. In particular, the ID will be fully replaced with a tracker completely made of Silicon, having higher granularity and radiation hardness. The R&D process for the new ATLAS ID is now ongoing. Different geometrical layouts are simulated and their performance is studied under different operating conditions in search for the optimal detector architecture. Also, the performance of the new Si-sensors/modules is under investigation with dedicated laboratory tests.

The focus of the project could be on the simulation of the High-Luminosity LHC version of the ATLAS Inner Detector. The student will learn how a high-energy physics experiment is designed and optimized. Alternatively, if possible at that moment, the student could work on a project at the Nikhef Silicon laboratory at the test-bench for new ATLAS Si-strip detectors and participate in the quality assurance procedure for the new ATLAS Si detectors.

ATLAS (4): Higgs productie in Run-2 van de LHC

In de eerste run van de LHC is onder andere bij het ATLAS experiment het Higgs deeltje gevonden. Nu is de tweede run begonnen en kan het Higgs deeltje worden bevestigd. Door de verhoogde energie ziet de achtergrond er echter heel anders uit, dus is de optimalisatie van het wegsnijden van de achtergronden qua fysica anders. Voor je bachelor project kan met behulp van de ATLAS detector het Higgs deeltje in run twee komen vinden.

Supervisors: Lydia Brenner, Wouter Verkerke

ATLAS (5): De lange staart van het Higgs boson

Na de ontdekking van het Higgs boson in 2012 zijn we druk bezig om te kijken of zijn eigenschappen overeenkomen met de voorspellingen van het Standaard Model. Een van de belangrijkste eigenschappen is de zogenaamde breedte van het Higgs boson. Als het Higgs boson naast de Standaard Model deeltjes ook in exotische nieuwe speeltje uit elkaar kan vallen (bijvoorbeeld donkere materie) dan zal dat ale eerste zichtbaar worden in een afwijking van de breedte tov de verwachting. We gaan in dit project uitzoeken hoe de strategie die nu gebruikt wordt (meten van de hoeveelheid Higgs bosonen met een extreem hoge massa) precies werkt en kijken of we door het toevoegen van nieuwe ideeën een verbetering kunnen aanbrengen.

Specifiek: We gaan eerst in detail de eigenschappen bekijken van het Higgs signaal en de twee achtergronden die er het meest op lijken. Daarna gaan we op zoek naar de verschillen en een manier waarop we onze kennis daarover kunnen gebruiken om gevoeliger te worden voor het Higgs signaal.

Supervisors: Hella Snoek, Ivo van Vulpen

E-mail: H.Snoek_at_nikhef.nl & Ivo.van.Vulpen_at_nikhef.nl

ATLAS (6): Project ATLAS-ITk

Voor de ATLAS upgrade van de binneste detector, de tracking detector ITk zal op Nikhef een groot onderdeel worden gebouwd: de End-Cap met een doorsnede van 2meter en 1.6meter lang. De silicium detectoren worden gekoeld met CO2, waarvoor een testopstelling ontwikkeld en doorgerekend moet worden. Hier ligt een flinke uitdaging voor een bachelorstudent die kennis heeft van thermodynamica en die affiniteit heeft met technische toepassingen. De berekeningen maken gebruik van een software pakket COBRA waar eventueel nog verfijningen in zijn aan te brengen. Het werk zal onder begeleiding plaatsvinden van ir Jesse van Dongen en dr Marcel Vreeswijk. (h73_at_nikhef.nl)

KM3Net

The KM3NeT collaboration is constructing a new generation neutrino telescope with a volume of several cubic kilometers (final configuration) in the deep waters of the Mediterranean Sea. With the data, scientists will look for the astrophysical sources of neutrinos such as supernovae, colliding stars or gamma-ray bursts. In the domain of particle physics the properties of neutrinos will be investigated, in particular the unknown neutrino mass hierachy.

The KM3NeT telescope detects the Cherenkov light emitted by the secondary particles produced in neutrino interactions using an array of thousands of sensitive 3 inch photo-multiplier tubes housed in 17 inch pressure resistant glass spheres, digital-optical-modules (DOMs), together with electronics. The DOMs are oriented along 700m long vertical lines, called detection units.

The first phase of the KM3NeT neutrino telescope is currently under construction, with the first two detection units operational at 3500m depth in the Mediterranean Sea, 100 km off the coast of Sicily.

KM3NeT (1): Photon counting in KM3NeT

The details of a neutrino interaction, such as its incoming direction and energy, determine the pattern, time and amount, of recorded photons (´hits´) by the photo-multplier tubes. The time of arrival is recorded with nanosecond accuracy and the amount of photons is encoded in the length of the pulse(time-over-threshold, ToT). Currently, only the photon arrival time and the number of photo-multipliers that record a hit are used in reconstructing event properties. In this project, the distributions of the ToT mainly originating from photons from potassium-40 decays in the sea-water and from atmospheric muons passing through the water will be studied. The goals are to investigate the properties of the ToT distributions obtained from data and simulation, in particular the dependence on the photo-multiplier efficiency and atmospheric muon flux. In this project we will be extensively using the programming language C++ to analyse the data, so a reasonable proficiency is required.

Supervisors: Ronald Bruijn & Karel Melis

Email: rbruijn_at_nikhef.nl

VIRGO

"It is anticipated that in the next few years, Advanced LIGO and Advanced Virgo will start observing gravitational waves from binary neutron star mergers. Prior to merger, as two neutron stars spiral towards each other, the tidal field of one star will cause a deformation in the other. These deformations affect the orbital motion, which in turn gets imprinted onto the gravitational wave signal. This way we can find out how deformable a neutron star is in the first place, which will yield information about the interior of neutron stars; the latter is the main open problem in nuclear astrophysics.

To succeed in this, good models are needed for the gravitational waveforms. The best model currently available which can be generated sufficiently fast on a computer to be useful in data analysis, contains a state-of-the art description of tidal effects, but not neutron star spins. It is generally assumed that neutron stars are slowly spinning, but it needs to be determined how measurements of tides would be affected by the absence of spins in our analyses.

In practice, the project will consist of learning how to use pre-existing gravitational wave data analysis tools, setting up simulations based on them, and interpreting the results."

The VIRGO collaboration operates the advanced VIRGO gravitational waves detector in Italy, and forms together with the LIGO collaboration a consortium that analyzes the data from both VIRGO and LIGO. For projects in the Nikhef VIRGO group, please contact Jo van den Brand (jo_at_nikhef.nl) or Chris van den Broeck (vdbroeck_at_nikhef.nl)

LHCb

Begeleider: Sean Benson

Title: Searching for physics beyond the Standard Model with LHCb

The LHCb experiment is designed to study the "The Flavour Problem" in particle physics: Why is the universe dominated by matter over antimatter? Why are there three generations of elementary particles? What is the origin of quark flavour changing interactions.

To solve these riddles, LHCb performs precision measurements on b-quark particle decays. An intriguing signal has recently been observed in the decay of a B-meson to a K* and two muons: Bd→K*μμ, which does not seem to behave according to the predictions of the Standard Model In this project the bachelor student will investigate this further by studying the case where the K* particle decays to a so-called k-short particle and a π0. The observation of such a final state will provide valuable information in the search for physics beyond the Standard Model.

In this ambitious project the student is expected to study both a theory on the mechanism of CP violation with B mesons, in addition to data analysis with B decays. Programming experience in python is required.

The LHCb experiment at CERN analyzes the properties of B-hadrons produced in proton-proton collisions at the LHC. For projects in the LHCb group, please contact Marcel Mark (marcel.merk_at_nikhef.nl)

LHCb (1)

One of the most fascinating mysteries in physics today is: how is it possible that universe is filled with matter? If the Big Bang produced equal amounts of matter and antimatter, we still do not understand the mechanism that lead to the excess of matter over antimatter that we observe today.

One interesting feature of some particles is that they can transform themselves into their antiparticles, then back to particle, and so forth, in an oscillatory way until they finally decay. In particular, beauty mesons (B) can oscillate into their antiparticle (B ̄). The parameters of this oscillation, such as amplitude, frequency and phase, are calculable mathematically: predictions for it are available in the standard model (SM) of particle physics. But the oscillations according to the SM alone would not lead to the imbalance of matter in the universe – we still need to find a new type of physics that may be able to explain it.

In this context, it is very important to measure B oscillations in the laboratory, and compare these observations with the expectations from the SM. Are the experimental data in good agreement with the SM, as we expect? If the aswer is not, i.e. if there are features of the oscillation that we do not understand well, then we may be observing “new physics”. In other words, the data may reveal a new mechanism that generates a different matter-antimatter balance than predicted by the SM, that may potentially solve the puzzle.

The LHCb experiment at CERN is dedicated to such studies: LHCb detectors are placed in a region along the LHC collider beamline, where a large number of B mesons are produced, arising from the proton-proton collision data from the LHC collider. Looking at the LHCb data we can obtain large samples of B mesons, and observe their oscillations. In this project we will learn how to select a sample of B mesons out of the data taken with the LHCb detector, measure the parameters that govern their oscillation and compare them with the SM.

For more information, please contact Mara Soares (msoares_at_nikhef.nl).