The Large Hadron Collider (LHC) at CERN in Geneva is the largest particle accelerator in the world. It collides protons at a centre-of-mass energy of 13.6 TeV, probing physics at the highest energy scales ever achieved in collider experiments. The biggest success of the LHC so far was the discovery of the Higgs boson by the ATLAS and CMS experiments in 2012, an elementary particle whose study is crucial for the understanding of the origin of elementary particle masses. Since 2022, the LHC has resumed operations at even higher collision rates, which provides plenty of opportunities to improve precision measurements of elementary particles as well as to extend the reach of searches for new particles beyond the standard model (SM) of particle physics.
The experimental particle physics group at UGent is involved in data analysis with the Compact Muon Solenoid (CMS) detector, covering a wide range of topics including precision measurements of SM processes, new physics searches, and calibration of detectors and reconstruction methods. All data analysis projects make use of the Python programming language and employ specific high-energy-physics software packages. Some basic knowledge of Python (or another programming language) is required, while more advanced programming skills will be taught during the project. After the completion of one of the data analysis projects, the students will have – Gained insight in the design, technology, and software of one of the most advanced particle detectors in the world; – Improved their programming skills in the field of data analysis and visualization, possibly including machine-learning techniques; – Got experience in taking part in an international environment at the frontier of fundamental research.
We offer the possibility of staying at CERN in Geneva/Switzerland for a summer project to all master students that join the CMS analysis group.
Shining light on top quarks: Measuring the interplay between the heaviest particle and the massless photon with the highest-energy LHC data
The production of top quark-antiquark pairs (tt̄) is one of the most common processes at the LHC. Top quark production is so abundant that the LHC is even nicknamed “top quark factory”, and tt̄ measurements are among the most precise cross section measurements ever performed by the CMS Collaboration. To study the electroweak interactions of the top quark, measurements of the production in association with a vector boson are a crucial tool. In this project, the CMS data collected in 2022 and 2023 will be analysed to identify tt̄ production events that contain additional photons (tt̄+γ). This will include careful studies of systematic effects in the identification of electrons, muons, and photons, as well as in the reconstruction of jets and tagging of jets originating from b quarks. The goal is to perform the first cross section measurement of top quark pair production as a function of the number of additional photons, and to constrain modifications introduced by physics beyond the standard model to the coupling between photons and top quarks.
Feynman diagrams for tt̄+γ production, where the photon orginates either from a top quark (left), an incoming quark (middle), or a charged lepton in the top quark decay (right). From: JHEP 05 (2022) 091.The distribution of the photon transverse momentum in tt̄+γ events, shown for standard model (SM) couplings between photon and top quark (yellow filled area) and for different scenarios with modified couplings induced by new-physics at a higher energy scale (red and blue lines). From: JHEP 05 (2022) 091.
Promoter: Prof. Didar DobuR Supervisors: David Marckx, Dr. Joscha Knolle Contact | Topic 37183 on PLATO
Exploiting lepton flavour universality to constrain Higgs boson decays to muons
Electrons (e), muons (μ), and tau leptons (τ) are very similar particles that only differ in their mass but have the exact same couplings in the electroweak theory. As a result, most high-energy processes at the LHC adhere to lepton flavour universality, i.e., have the same probabilities for the three lepton flavours. The notable exception are Higgs boson (H) processes, since the strength of the Yukawa coupling between fermions and the Higgs boson are proportional to the fermion mass. Thus, Higgs bosons are much more likely to decay to τ⁺τ⁻ than to μ⁺μ⁻, and will almost never decay to e⁺e⁻. In this project, we will investigate top quark pair (tt̄) production in association with a Z boson and compare the selection efficiencies in Z→e⁺e⁻ and Z→μ⁺μ⁻ events. The goal is to use the observed number of tt̄+e⁺e⁻ events in data to predict the yield of tt̄+μ⁺μ⁻ events. This can then be applied to predict the standard model background for searches of tt̄H production with H->μ⁺μ⁻ decays from tt̄+e⁺e⁻ events, which have negligible contributions from tt̄H.
Summary of the coupling strengths between the Higgs boson and the different bosons and fermions as a function of the boson/fermion mass, as measured with the CMS experiment. The muon is the first second-generation fermion whose coupling with the Higgs boson is being measured, and the uncertainty is still very large. From: Nature 607 (2022) 60. Number of events as a function of the lepton type in a tt̄Z measurement. The tt̄Z signal is shown in red, and different background sources with other colours. While tt̄Z decays to the different lepton combinations with equal opportunities, the observed yields are different since the efficiency to reconstruct and select a muon is higher than for electrons. From: CERN-THESIS-2020-185.
Promoter: Prof. Didar DobuR Supervisors: Jules VandenBroeck, Dr. Joscha Knolle Contact | Topic 37184 on PLATO
At the mass frontier: Measuring four simultaneously produced top quarks in final states with hadronically decaying tau leptons
The top quark is the heaviest known elementary particle with a mass of about 173 GeV, and consequentially the simultaneous production of four top quarks (tt̄tt̄) is an extremely rare process to occur at the LHC. Still, the UGent CMS analysis group achieved the first observation of tt̄tt̄ production by analyzing events with two same-sign, three, or four electrons and/or muons (so-called “multilepton” events). In this project, we will build upon this great success and add the reconstruction of hadronically decaying tau leptons to the analysis strategy. By selecting multilepton events where one of the leptons is a tau lepton, we can improve the statistical uncertainty of the measurement and thus derive stricter constraints on new-physics scenarios with so-far unknown heavy particles that would modify tt̄tt̄ production. The goal is then to train a machine-learning discriminant to separate tt̄tt̄ production from the main background processes using information from the reconstructed electrons, muons, tau leptons, and jets in the event.
Left: Distribution of the number of b jets in multilepton events, with the tt̄tt̄ contribution shown in red and different background contributions in other colours. Since the background contributions are much larger than the signal, a machine-learning discriminant is trained to separate tt̄tt̄ from the background. Right: Distribution of the resulting machine-learning discriminant in events with a same-sign electron-muon pair. The purity of the tt̄tt̄ signal is much higher than in the plot on the left. From: Phys. Lett. B 847 (2023) 138290.
Promoter: Prof. Didar DobuR Supervisors: Niels Van den Bossche, Dr. Joscha Knolle Contact | Topic 37187 on PLATO
Into uncharted territory: Disentangling the interplay between Higgs, W, and Z bosons in associated top quark pair production
Associated production of a top quark pair (tt̄) with other particles is an important area of study: On the one hand, tt̄+X measurements probe the electroweak interactions of the top quark and thus help to improve our understanding of the SM. On the other hand, new physics beyond the SM is expected to be relevant at high energy scales, and thus be more noticeable in very massive final states like tt̄+X. Previous results include precision measurements of tt̄ production in association with one massive boson (Higgs, Z, or W boson) and the observation of tt̄tt̄ production. In all these measurements, tt̄ production in association with two vector bosons (tt̄VV) is a relevant background process, but it has not been measured independently. In this project, we will develop analysis strategies to measure tt̄WW, tt̄WZ, and tt̄ZZ production. The goal is to find observables that allow for the separation of these processes from background events, potentially using machine-learning techniques to develop an optimized discriminant.
Example Feynman diagrams for tt̄WW (left), tt̄WZ (middle), and tt̄ZZ (right) production. These possible diagrams involving a three- or four-boson interaction (indicated with a dot) demonstrate the potential of tt̄VV measurements to probe the purely bosonic interactions predicted in electroweak theory.Event distribution in a tt̄tt̄ measurement using events with two same-sign and three charged leptons, showing the distribution of the machine-learning discriminant that sorts tt̄tt̄ (red area) to the right and background contributions (other coloured areas) to the left. Visible is also the tt̄VV background contribution in light blue. From: Eur. Phys. J. C 80 (2020) 75.
Promoter: Prof. Didar DobuR Supervisors: Niels Van den Bossche, Dr. Joscha Knolle Contact | Topic 37191 on PLATO
Towards quantum state tomography with elementary qutrits: Measuring spin correlations in diboson events
Quantum state tomography refers to the determination of the spin density matrix of a quantum mechanical system from an ensemble of measurements of similarly prepared states. The production of a specific final state at the LHC provides such an ensemble of similarly prepared states, and can thus be used to measure the spin density matrix of a system of elementary particles. So far, spin correlations have been measured only for top quark-antiquark pair (tt̄) production, where the spin-½ particles with two possible polarization states can be treated as “qubits”, recently resulting in the observation of quantum entanglement in tt̄ events. In this project, we will study the spin correlations in the production of WZ diboson events. Massive spin-1 particles have three possible polarization states and are thus treated as “qutrits”. Leptonic decays of the W and Z boson will lead to events with three charged leptons, and we will devise analysis strategies to reconstruct distributions of angular separations between the charged leptons and to extract the spin correlation coefficients from these distributions.
Angle of the charged lepton from the W boson decay in WZ production events, shown separately for longitudinal (”0”), left-handed (”L”), and right-handed (”R”) polarization. From a measurement of this angular distribution, the fractions of the different polarization states can be measured. Other angular distributions will be investigated for the measurement of spin correlations. From: JHEP 07 (2022) 032.Lower bound on the concurrence as a function of the production angle and the invariant mass of the WZ system in WZ production events. A state is entangled if the concurrence is larger than zero. In the standard model, WZ production events are most entangled (yellow areas) for large production angles and small invariant masses, and for smaller production angles but much larger invariant masses. Entanglement can be measured from spin correlation observables. From: R. Aoude et al., JHEP 12 (2023) 017.
Promoter: Prof. Didar DobuR Supervisors: Maarten De Coen, David Kavtaradze, Dr. Joscha Knolle Contact | Topic 37194 on PLATO
How to count pp collisions: Using Z boson events as a standard candle to integrate the 2024 luminosity
A crucial ingredient to precision cross section measurements at a collider experiment is the precise knowledge of the integrated luminosity, which quantifies the total number of collisions from which experimental data was recorded. At the CMS experiment, the luminosity measurement is calibrated with data recorded during one special day, and then integrated over the full data-taking period. Uncertainties arise from the extrapolation of the calibration over time, since e.g. changes in the detector conditions from aging, radiation damage, or operational changes can result in a reduced response of the detectors. In this project, we will implement a measurement of Z→μ⁺μ⁻ in short time intervals of about 30 minutes for the data to be recorded in 2024. Since this process is well known and occurs at a high rate, the “tag-and-probe method” can be applied separately in each time interval to measure the efficiency of the muon reconstruction and selection. In the tag-and-probe method, the event yields are compared for two classes of events: where both muons pass a certain reconstruction step, and where only one muon passes this reconstruction step. The difference in yields corresponds to the reconstruction efficiency. By measuring the efficiencies separately in each time interval, no time extrapolation needs to be made, and the “Z counting” rate can be measured precisely over the whole data-taking period. This can then be used to obtain a precise integration of the luminosity measurement.
Example fit results for the tag-and-probe measurement of the trigger (”HLT”) efficiencies. In the left plot, only one of the two muons has passed the trigger selection, whereas in the right plot, both muons have passed the trigger selection. The number of events is shown as a function of the invariant mass of the dimuon system. From the yields in the ”passing” and ”failing” categories, the trigger efficiency can be extracted. From: Eur. Phys. J. C 84 (2024) 26.Extracted luminosity measurement (left) and efficiencies of the different selection steps (right) during 10 hours of data-taking in 2022. The efficiencies are not constant but change as a function of time, and it is thus important to measure the efficiencies separately in each time interval rather than assuming a constant efficiency over the whole 10 hours. From: CMS-DP-2023-003.
Promoter: Prof. Didar DobuR Supervisors: Maarten De Coen, Dr. Joscha Knolle Contact | Topic 37196 on PLATO
How close are bees at the CMS experiment? Study of collimated bottom quark pairs in top quark pair production events at the LHC
The production of a pair of top quarks and a pair of bottom quarks (ttbb) is an important background process of Higgs boson production in association with a pair of top quarks (ttH), or the production of four top quarks (tttt), the discovery of which are two major milestones achieved at the LHC! Due to the production of the process fully through the strong interaction, the ttbb process is difficult to estimate and predict with simulation, so precise measurements of this process in data is important. The UGent CMS analysis group has achieved a measurement of this process in cases where the bottom quarks are spatially separatable (arXiv:2309.14442). A so far unexplored feature of this process is the collimated production of the pair of bottom quarks, which is equally important for an improved understanding of the ttbb process.
In this project, we will study the behaviour of the ttbb process in cases where the bottom quarks are produced close to each other. For this purpose, we will first perform a study of simulated ttbb events to gauge the expected kinematic features of these bottom quark pairs, such as their opening angles, momenta or invariant mass. We will follow this up with a design of event selections for data analysis to set the baseline for measuring this part of the ttbb process in data. We will also explore how this collimated process contributes as background to the measurements of ttH production where the Higgs boson decays into a pair of collimated bottom quarks.
More information on the tttt and ttH discoveries are highlighted here and here.
One of the key results of the measurement of the ttbb process, showing the production probability as a function of the opening angle of the bottom quark pair, and a comparison of the data (black) with different predictions from simulation. Specifically interesting for the master project will be zooming into the first bin, where the angle is very small.A representative Feynman diagram of ttbb production.
Promoter: Prof. Didar DobuR Supervisors: David Kavtaradze, Dr. Jan van der Linden Contact | Topic 37203 on PLATO
Reducing the difference of simulation and data at the CMS experiment: Applying machine-learning based scale factor methods to b jet identification
At the CMS experiment we heavily rely on the simulation of collision events with Monte Carlo simulation tools. With the simulated events we can make comparisons to the data recorded at the CMS experiment and measure many different processes, particles, or quantities. For this purpose, it is particularly important to validate that the simulation is as close as possible to the recorded data. Imperfections in the simulation are corrected via so-called “scale factors”. One area where we need scale factors is for the identification of b quark jets (collimated particles originating from the hadronization of b quarks produced in the proton-proton collisions), for which we employ modern machine-learning algorithms to identify such b jets. In the UGent CMS analysis group, we are currently working on developing new scale factor methods based on machine-learning models, which are designed to learn differences in the simulation and data, and use this knowledge in adversarial neural-network architectures to learn the scale factors needed to equalize simulation and data.
In this project, we want to explore different network architectures, all following adversarial training approaches, to identify promising candidates for this machine-learning based scale factor method. As one example, we want to test the performance of the DCTR approach (arXiv:1907.08209) for this problem. After some explorations of the machine-learning aspects of this project we want to apply the new scale factor methods to an existing data analysis, and compare the new method with the already established scale factor methods in CMS. This validation of the performance in a real analysis example is important aspect of establishing new methods in the CMS Collaboration. The project has the potential of making important contributions to many future data analyses at the CMS experiments.
Further reading on the basic idea of this project can be found e.g. here.
The figure shows the output probability distribution of a jet tagging algorithm (deepJet) for identifying bottom quark jets versus charm quark jets. The probability distribution for data is shown as black points, and from simulated events as coloured histograms. The differences between data and simulation are highlighted in the lower ratio panels. The differences between simulation and data seen in the left plot are reduced with the established scale factor methods employed in CMS (right plot). The goal of this project is to develop updated strategies of obtaining these scale factors with machine-learning methods. Figures from JINST 17 (2022) P03014.
Promoter: Prof. Didar DobuR Supervisors: David Kavtaradze, Dr. Jan van der Linden Contact | Topic 37205 on PLATO
Implementation of algorithms for charged-particle track reconstruction at CMS
An accurate estimate of the particle’s trajectory parameters based on obtained measurements is one of the core tasks in event reconstruction algorithms. The Kalman Filter (KF) is a well-known optimal estimator for linear systems that proved to be an excellent solution for charged-particle track reconstruction at the Large Hadron Collider (LHC) experiments at CERN. The main topic of this project is devoted to the implementation of the KF algorithm using detector-level data recorded by the CMS experiment and its optimization for various collision event topologies. A dedicated parallel-computing implementation of the initial step in track reconstruction to find seeding elements using a GPU computing cluster at UGent will be done, as well as the comparison to its CPU-based counterpart.
An event display view of the CMS tracker (contained within the ECAL barrel) looking along the beam pipe, with reconstructed tracks.
Promoter: Prof. Didar DobuR Supervisor: Dr. Kirill Skovpen Contact | Topic 37395 on PLATO
Detector topics
Characterization of silicon photomultipliers
The silicon-based detectors are widely used in various particle-physics experiments. The silicon sensors are the intrinsic part of the particle tracking systems as well as fast calorimeter readout. The goal of the proposed project is to build a characterization system to perform comprehensive studies of the silicon photomultipliers (SiPMs). The characterization stand will serve as the main quality control procedure in testing the SiPM modules at UGent. The student(s) will get familiar with the functioning of SiPM detectors and work on establishing the core methodology to measure the dark current and amplification parameters of the modules. The study of SiPMs will also touch upon the detection of cosmic muons using plastic scintillators.
Promoter: Prof. Didar DobuR Supervisor: Dr. Kirill Skovpen Contact | Topic 37306 on PLATO
Development of the atmospheric muon telescope at UGent
Atmospheric muons produced in the air showers triggered by high-energetic particles coming from astrophysical sources serve as an excellent tool to study the performance of various particle-physics detector modules. A well-established approach in particle-physics applications is to use a configuration of two parallel scintillators as a telescope detector to identify muon tracks. The project will include the construction and commissioning of the prototype of the atmospheric muon telescope using plastic scintillators coupled to silicon photomultipliers for signal readout. This telescope will be used in various research activities involving the testing of the CMS detector modules and studies of atmospheric muon fluxes. The construction activities and optimization of the telescope performance through a detailed data analysis will be done. Students should have a strong interest in particle-physics detection techniques and data readout strategies.
Promoter: Prof. Didar DobuR Supervisors: Dr. Kevin Mota, Dr. Kirill Skovpen Contact | Topic 37313 on PLATO
Feasibility study of soil moisture monitoring using scintillation detectors
The scarcity of water resources is naturally connected to the process of climate change. The project explores the possibility of Improving water management in irrigation practices in farming applications through the development of innovative cosmic-ray neutron sensors as a completely non-invasive method to assess the volumetric water content in agricultural soils. The thermal neutron fluxes are proposed to be measured using scintillation detectors. The study will use various simulation techniques to model the atmospheric flux of neutrons, its interaction with the soil in the ground, and the eventual detection of these particles in a scintillator. The above-ground presence of thermal neutrons will be studied as a function of altitude, soil type, and atmospheric conditions.
Promoter: Prof. Didar DobuR Supervisor: Dr. Kirill Skovpen Contact | Topic 37396 on PLATO
Study of the performance of muon detectors at CMS
Muon detectors are vital for a reliable muon identification in the CMS detector at Large Hadron Collider (LHC) at CERN. In preparation for future experiments at the High-Luminosity (HL)-LHC, the CMS detector is going through a major upgrade procedure to replace and improve its key detector systems, including the Muon detectors. Within this project, we will build a simulation model using GEANT4 and Garfield++ simulation packages to study in detail the response of gaseous detectors to various incoming particles as well as configuration of the electric field. You will also have a unique opportunity to join research activities to analyse data from the new detector modules: Resistive Plate Chambers (RPCs) as well as Gas Electron Multiplier (GEM) chambers, with an in-depth analysis of their performance characteristics and quality control. Students are expected to be interested in particle-physics detection techniques and eager to become experts in gaseous detectors and their application to the field of high-energy physics.
Garfield simulation of an electron avalanche in a GEM foil.
Promoter: Prof. Didar DobuR Supervisors: Dr. Kevin Mota, Dr. Kirill Skovpen Contact | Topic 37397 on PLATO
Future collider topics
Study of the top quark reconstruction at future-collider experiments at CERN
Study of the properties of the heaviest elementary particle of the standard model of particle physics, the top quark, is among the foremost goals of the ongoing experiments at the Large Hadron Collider (LHC) at CERN. Future collider projects aim at further improving the precision of these measurements, setting stringent limits on the new physics phenomena. The goal of the proposed task is to develop an algorithm to reconstruct the top quark using simulated events produced in electron-positron collisions at the Future Circular Collider (FCC) factory – a major international project at CERN. The implemented algorithm will serve as the main tool to identify top quarks at FCC and perform the measurements of various physics processes including this particle. The student(s) will work with data stored within the ROOT Data Analysis Framework using Python scripting tools for data analysis and plotting.
Map of the Geneva area with the location of the LHC and a possible location of the FCC. From the CERN Courier.
Promoter: Prof. Didar DobuR Supervisors: Dr. Kevin Mota, Dr. Kirill Skovpen Contact | Topic 37302 on PLATO
Gravitational waves data analysis topics
A novel approach to discover unmodelled features and exotic gravitational waves sources
Current gravitational-wave (GW) searches rely heavily on modelling, in which General Relativity (GR) simulations are employed to construct gravitational waveforms. These parametrized waveforms encapsulate the most important features of a GW signal. The waveforms are then employed to identify GW events in the detector strain data, and subsequently to perform parameter estimation (PE) on the event. This approach works very well for detecting binary black hole (BBH), neutron star-black hole (NSBH) and binary neutron star (BNS) events. However, this methodology is not suitable for features that are not accounted for in the modelled waveforms, or to GW signals originating from sources of another nature, like core collapse supernovae or other exotic objects.
Gravitational “waveform” of the binary black hole merger GW150914. From: B. P. Abbott et al. “Observation of Gravitational Waves from a Binary Black Hole Merger” Phys.Rev.Lett. 116 (2016) 6, 061102, arXiv:1602.03837.
In this project, you will attempt to use this lack of modelling to your advantage. By deliberately utilizing waveforms that inadequately capture simulated GW signal features, you will investigate their impact on posterior samples obtained in the PE process. If discernible, these effects could be indicative of unmodelled features, prompting the development of a custom machine learning (ML) algorithm to detect such manifestations in real GW event data.
You will first perform normal PE runs on simulated/real GW events. Once you are accustomed with the workflow, you will adjust the code to use wavelets to reconstruct the inadequately modelled features, establishing a setup to run on simulated GW events with all known features. Subsequently you will develop a general ML tool to identify the signatures of the unaccounted-for features in the resulting data.
An unmodelled Morlet-Gabor “wavelet” which can be used as a basis element to reconstruct the signal.
The work involved will be computational. You will learn about statistical and machine learning methods. You will be involved in a large international collaboration in the forefront field of GW science.
Promoter: Prof. Archisman Ghosh Supervisor: Freija Beirnaert Contact | Topic 37327 on PLATO
Hunting for exotic resonances in compact binary mergers
Is it possible that the black hole-like compact objects which we are observing in gravitational waves (GWs) are not really black holes, but exotic compact objects mimicking black holes. Several such exotic alternatives have been proposed in literature. They include stars composed of exotic matter such as boson stars, dark matter stars, gravastars or else horizonless compact objects arising from quantum modifications to gravity, such as firewalls and fuzzballs [V. Cardoso & P. Pani, Living Rev. Rel. 22 (2019), arXiv:1904.05363]. The internal physics of such objects is expected to show up in the GW signal from their coalescence. However since their exact nature is unknown, a part of the GW signal from them cannot be modelled. In order to search for them, one needs to proceed with a combination of modelled and model-agnostic methods [K. W. Tsang et al., Phys.Rev.D 98 (2018) 2, 024023, arXiv:1804.04877].
In this project, you will search for resonances in the internal fluid modes which can be triggered during the inspiral of a binary of such an exotic compact object. An overall “dephasing” can be expected due to the energy lost in the resonance. In addition, you will try to reconstruct the resonance part of the signal using an unmodelled basis of simplistic “wavelets”.
An unmodelled Morlet-Gabor “wavelet” which can be used as a basis element to reconstruct the signal.
The work involved will be computational. You will learn about statistical methods (Bayesian statistics) and get exposed to state-of-the-art data analysis techniques. The work will be integrated into the activities of the Testing GR group of the LIGO-Virgo-KAGRA Collaboration. You will be involved in a large international collaboration in the forefront field of GW science.
Promoter: Prof. Archisman Ghosh Supervisors: Cezary Turski Contact | Topic 37329 on PLATO
Measuring the Hubble constant with LIGO-Virgo-KAGRA data
The fourth observing run (O4) of the LIGO-Virgo-KAGRA (LVK) gravitational-wave (GW) detector network began in May 2023 and is expected to run until December 2024.
After interesting candidate events have been identified and their parameters have been measured, it will be time to obtain science results out of the observations. A central role played by researchers in UGent is in the Cosmology working group of the LVK. A short-term goal of this group is to measure the Hubble constant, H0, the local expansion rate of the universe. One uses the GW distance measurement together with complementary redshift information (from possible electromagnetic counterparts, host galaxies, or galaxy clusters) to infer the cosmological parameters such as H0. Due to a tantalizing discrepancy between the local and early-universe measurements of H0, now dubbed as the “Hubble tension,” such an independent measurement of H0 from the GW sector can prove to be invaluable.
The latest measurement of the Hubble constant by the LIGO-Virgo-KAGRA Collaboration. From: B. P. Abbott et al., arXiv: 2111.03604.
In this project you will work with researchers who have developed the LVK codebase gwcosmo+ for cosmology inference and have put together the upGLADE galaxy catalogue to go along with it. You will be a part of the team that carries out the first cosmology analyses on O4 data. If we are lucky, we may observe a multimessenger signal in O4 and get to analyze the data from it. Until now, we have seen only one such multimessenger signal, namely GW170817.
The work involved will be computational. You will learn about statistical methods and get exposed to state-of-the-art data analysis techniques. You will be involved in a large international collaboration in the forefront field of GW science.
Promoter: Prof. Archisman Ghosh Supervisors: Freija Beirnaert, Cezary Turski Contact | Topic 37333 on PLATO
Observational science challenges with the Einstein Telescope
The Einstein Telescope (ET) will have more than ten times the sensitivity of the current LIGO-Virgo-KAGRA detector network. As a result we will see merging black holes which are much farther away (out to the edge of the known universe), as well as heavier black holes, (thousands of times the mass of the sun), which merge at lower frequencies made accessible by the ET. Typical signals observed by the ET will also be much longer – minutes to hours or even longer (as opposed to a fraction of a second for the current detector network). This is exciting. However it brings forth several computational challenges. How will we carry out data analysis for such long signals? Signals will certainly overlap – how will we disentangle them from each other? The ET Collaboration Observational Science Board was recently established to answer such questions.
In this project, you will develop prospective techniques for ET data analysis. In particular, you will attempt to bring together traditional methods such as Bayesian Markov Chain Monte Carlo (MCMC) together with more recently developed Convolutional Neural Network (CNN) algorithms with the goal of efficiently analyzing multiple signals present simultaneously in the data.
The work involved will be computational. You will learn about statistical methods and get exposed to state-of-the-art data analysis techniques. You will be involved in a large international collaboration in the forefront field of GW science.
Promoter: Prof. Archisman Ghosh Supervisor: Freija Beirnaert, Cezary Turski Contact | Topic 37334 on PLATO
Gravitational waves instrumentation topics
Optical layout of the ETpathfinder
The direct detection of gravitational waves (GWs) is a breakthrough discovery of recent years. The several GW detections by the Advanced LIGO and Virgo detectors, since they were first discovered in 2015, have opened up a new window to the observable universe. The current “second generation” detectors are Michelson interferometers with km-scale arms. The principle behind the detector is based on the fact that when a GW passes through, the arms of the interferometer are stretched and squeezed in opposite ways in the two directions.
Effect of a gravitational wave (propagating in the direction perpendicular to the plane of the paper) on the arms of a Michelson interferometer.
The current detectors will eventually be replaced by the next generation of GW detectors of significantly higher sensitivity and distance reach. One of these “third generation” detectors is the Einstein Telescope (ET), which is planned to be built in Europe in the 2030s. Fundamentally new technology will be required to go beyond the limitations of the current detectors. Extensive work and study is required for each of the new techniques to be implemented. ETpathfinder is an R&D facility, located in Maastricht, the Netherlands, with the aim to test these new techniques and to give important inputs for the design and the construction of third generation GW detectors like ET. The ETpathfinder is a Fabry-Perot Michelson interferometer with 10 m arm cavities working at cryogenic temperatures. It will mainly focus on developing prototypes and testing cryogenic temperatures (120 K, 15 K), new mirror material (Silicon), new laser wavelengths (1550 nm, 2090 nm), and advanced quantum noise reduction techniques.
Ghent University has been involved in the ETpathfinder project since its beginning. The facility in Maastricht is currently still under construction, with the aim to have the interferometer up and running by the end of this year.
Although the layout of ETpathfinder is broadly defined, optical simulations are needed to define position and specifications of all auxiliary optics used to have the proper beam parameters at each step of the path. You will be actively involved in the development of ETpathfinder, working on optical simulations to define the final layout.
You will be a member of the Einstein Telescope Collaboration. You will get involved with the technology and challenges of interferometric detectors in the active field of gravitational-wave science. The project will be done in close coordination with the ETpathfinder community. Travel to Maastricht, where the facility is located, may be required.
Simplified layout of ETpathfinder in its first phase.Picture of the ETpathfinder hall with all the vacuum towers assembled.
Promoter: Prof. Archisman Ghosh Supervisor: Dr. Daniela Pascucci Contact | Topic 37340 on PLATO
Optical characterization of 2μm photodetectors
The direct detection of gravitational waves (GWs) is a breakthrough discovery of recent years. The several GW detections by the Advanced LIGO and Virgo detectors, since they were first discovered in 2015, have opened up a new window to the observable universe. The current “second generation” detectors are Michelson interferometers with km-scale arms. The principle behind the detector is based on the fact that when a GW passes through, the arms of the interferometer are stretched and squeezed in opposite ways in the two directions.
Effect of a gravitational wave (propagating in the direction perpendicular to the plane of the paper) on the arms of a Michelson interferometer.
The current detectors will eventually be replaced by the next generation of GW detectors of significantly higher sensitivity and distance reach. One of these “third generation” detectors is the Einstein Telescope (ET), which is planned to be built in Europe in the 2030s. Fundamentally new technology will be required to go beyond the limitations of the current detectors. Extensive work and study is required for each of the new techniques to be implemented. ETpathfinder is an R&D facility, located in Maastricht, the Netherlands, with the aim to test these new techniques and to give important inputs for the design and the construction of third generation GW detectors like ET. The ETpathfinder is a Fabry-Perot Michelson interferometer with 10 m arm cavities working at cryogenic temperatures. It will mainly focus on developing prototypes and testing cryogenic temperatures (120 K, 15 K), new mirror material (Silicon), new laser wavelengths (1550 nm, 2090 nm), and advanced quantum noise reduction techniques.
Next generation GW observatories such as the Einstein Telescope (ET) will use silicon mirrors as test masses to detect low frequency GW with unprecedented sensitivities. This implies the use of new laser wavelengths at 1550nm or 2090nm. The performance of such optics will be first tested at the ETpathfinder facility in Maastricht. To detect the main interferometer signal, coming from the GW strain, photodiodes with a high quantum efficiency (HQE) and a large dynamic range for these new wavelengths are needed. At 1550nm HQE InGaAs sensors exist, however at 2090nm more development is needed and custom made extended InGaAs photodiodes with optimized quantum efficiency, especially for 2090 nm, will need to be acquired and tested. In this project we will contribute to the development of such novel 2090nm HQE photodiodes by performing optical characterizations of available photodiodes.
UGent has recently set up an optical lab for characterization of optical components for 2090nm. You will set up a measurement system at UGent optical lab with existing readout electronics (available in UAntwerpen) to test the sensor for e.g. dark noise, efficiency, and optical power levels.
The work involved will be hands-on instrumentational, with focus on optics and mechanics. The project will be under joint supervision with Prof. Hans Van Haevermaet (UAntwerpen). You will also get a chance to work at the ETpathfinder facility in Maastricht and be a part of the exciting activity in the Belgian-Dutch region centred around the Einstein Telescope.
Promoters: Prof. Archisman Ghosh, Prof. Hans Van Haevermaet (UAntwerpen) Supervisor: Dr. Daniela Pascucci Contact | Topic 37342 on PLATO
