Master's Theses on Data Analysis
| Topic: | Correlation of Beam Background and Accelerator Parameters with Detector Performance in the Belle II Experiment |
| Summary: | The Belle II experiment at the SuperKEKB accelerator faces significant challenges due to high beam background originating from the extreme accelerator conditions. They affect key performance metrics such as tracking efficiency and calorimeter photon energy resolution. This project aims to investigate the impact of beam background on detector performance. We currently use two proxies to measure the level of beam background: out-of-time crystals (photons detected outside the expected timing window) and extra CDC hits (additional drift chamber hits not used by any tracking algorithm). The primary goal is to improve these proxies by applying anomaly detection techniques, specifically autoencoders, to identify anomalous beam conditions that correlate with performance degradation. Both simulation and real data from Belle II will be used for model training. Additionally, the project will incorporate time series data from the SuperKEKB accelerator, including thousands of sensor readings and accelerator parameters, to correlate operational conditions with fluctuations in detector performance. The first stage of this project involves developing a more precise method for measuring beam background and analyzing how accelerator conditions affect the performance of the Belle II detector. The final stage aims to identify key accelerator parameters from SuperKEKB data in order to define operational margins that ensure sufficient performance of the experiment. |
| What you will learn: | Python programming, data analysis |
| Advisor: | Prof. Dr. Torben Ferber |
| Contact: | Jonas Eppelt |
| Last change: | 27.11.2024 |
| Topic: | Search for dark photons and axionlike particles in single-photon events at Belle II |
| Summary: | Belle II is a world-leading experiment in the search for dark sector candidates in the GeV range, such as dark photons or axion-like particles (ALPs). Invisibly decaying or long-lived dark photons and ALPs give rise to events with a single, monochromatic photon in the event, a unique and very challenging experimental signature. You will join our team our team to work on this search, which is currently focused on on-shell dark photons, with the aim of extending it to so-called off-shell (heavy) dark photons and ALPs. You will learn how to use tools for generating simulated datasets with Monte Carlo techniques and for statistical analysis. |
| What you will learn: | Python programming, data analysis, statistics |
| Advisor: | Prof. Dr. Torben Ferber |
| Contact: | Dr. Giacomo De Pietro |
| Last change: | 27.11.2024 |
| Topic: | Search for long-lived dark photons decaying into visible final states at Belle II |
| Summary: | Among all the dark sector searches, the Belle II experiment has a unique sensitivity to a weakly coupled dark photon whose decays have a displaced vertex. You will start a new search for long-lived dark photons decaying into a pair of muons, pions, kaons and, more challenging, electrons, with the aim of exploring previously unexplored parameters’ space. You will learn how to characterise the detector performance for the reconstruction of displaced vertices and use tools for statistical analysis. |
| What you will learn: | Python programming, data analysis, statistics |
| Advisor: | Prof. Dr. Torben Ferber |
| Contact: | Dr. Giacomo De Pietro |
| Last change: | 27.11.2024 |
| Topic: | Search for B+/0 → π+/π0/ρ+/ρ0 νν decays at Belle II experiment |
| Summary: | Recently the Belle II experiment set a stringent limit on the branching fraction for the rare decay B+ → K+νν, which is b → s transition, using a novel tagging approach which relies heavily on a machine learning-based selection. The measurement of the branching fraction for this decay is of great interest as it is strongly sensitive to many NP scenarios, such as leptoquarks, axions or other dark matter candidates. In this project, you would perform the first search with Belle II data for very similar processes also using machine learning-based selection, but instead of b → s transitions, you would search for b → d transitions B+/0 → π+/π0/ρ+/ρ0 νν, where the branching fractions in the SM are further suppressed by |Vtd/Vts|^2. |
| What you will learn: | machine learning, python programming, data analysis, statistics |
| Advisor: | Prof. Dr. Torben Ferber |
| Contact: | Dr. Slavomira Stefkova |
| Last change: | 15.10.2024 |
| Topic: | Search for B+ → (ccbar → ν̄ν) K+ with Belle II |
| Summary: | In this project, search for a process of B+ → (ccbar → ν̄ν) K+ where ccbar is one of the resonant states such as J/psi which decays invisibly. In the SM this decay is mediated by Z Bosons and the branching fraction for this decay is expected to be tiny. However, beyond SM physics, such as new Z’ Bosons, could enhance the branching fraction significantly. For this search you will work on an analysis which will use so called "exclusive hadronic tagging" for the other B in the event before looking for a signal decay of interest within the rest of the event. Development of the rest of the selection will include an implementation of machine learning algorithms that will be trained in order to suppress backgrounds. |
| What you will learn: | machine learning, python programming, data analysis, statistics |
| Advisor: | Prof. Dr. Torben Ferber |
| Contact: | Dr. Slavomira Stefkova |
| Last change: | 15.10.2024 |
| Topic: | Search for B+→l nu gamma at Belle II |
| Summary: | The radiative leptonic decay B+ -> l+nu gamma yields important information for the theoretical predictions of non-leptonic B meson decays into light-meson pairs. The emission of the photon probes the first inverse moment λ_B of the light-cone distribution amplitude (LCDA) of the B meson. This parameter is a vital input to QCD factorisation schemes for the non-perturbative calculation of non-leptonic B meson decays. This project aims to observe the B+→l+nu gamma decay for the first time and set an improved limit on λ_B using modern machine learning analysis techniques. |
| What you will learn: | python programming, data analysis |
| Advisor: | Prof. Dr. Torben Ferber |
| Contact: | Dr. Pablo Goldenzweig |
| Last change: | 15.10.2024 |
| Topic: | Search for Bs→φπ0 decays at Belle |
| Summary: | The Belle experiment, which concluded in 2011, collected a unique sample of Υ(5S) decays to Bs meson pairs in the clean e+e- collision environment. This dataset has yet to be fully exploited. The rare decay Bs→φπ0 is strongly suppressed in the Standard Model and has yet to be observed. However, in a theoretical analysis motivated by the Kπ CP-puzzle, models with modified or additional Z bosons allow for an increase of the branching fraction by an order of magnitude without inconsistencies with other measurements. The Kπ CP-puzzle consists of an unexpectedly large direct CP asymmetry in the decays B± → K±π0 and B0 → K±π∓. These decays are dominated by isospin-conserving processes, but have a small contribution from isospin-violating penguin processes as well. In the isospin-violating decay Bs→φπ0 the penguin processes dominate, which means that potential NP contributions can have a much larger relative effect. If these contributions exist, an observation of the Bs→φπ0 decay may be possible with the Belle Υ(5S) dataset. |
| What you will learn: | python programming, data analysis |
| Advisor: | Prof. Dr. Torben Ferber |
| Contact: | Dr. Pablo Goldenzweig |
| Last change: | 15.10.2024 |
| Topic: | Bs→K+ l- nu with Y(5S) using machine learning-based Full Event Interpretation |
| Summary: | There are two conceptually different methods to determine the CKM matrix element Vub, a factor in the amplitude of transitions from a b-quark to a u-quark and a W boson. As quarks cannot be detected directly, one has to handle the hadronisation to infer Vub, even in the simplest case, where the W boson decays into a charged lepton and a neutrino. One method, which is easier to calculate but is experimentally more challenging, takes into account all possible final states that typically occur during the hadronisation process (inclusive measurement). The other involves calculating the hadronisation effects and searching for only a single final state, e.g., B0->pi-l+nu (exclusive measurement). Both approaches have been pursued and the result is a tantalizing 3sigma discrepancy between the measurements of the same quantity Vub. By measuring Bs->K-l+nu we can shed light on the possible reasons or sources for this, as we replace the spectator d quark in B0->pi-l+nu with an s quark. Since the calculation of the hadronisation in the exclusive measurement relies on Lattice QCD, the kaon in the final state simplifies the calculation significantly. A result close to the existing exclusive measurement would strengthen the trust in that measurement and could hint to new particles beyond the Standard Model. A result closer to the inclusive measurement would more likely be interpreted as a hint that the calculations for the exclusive measurement are unreliable and that the inclusive measurement gives the real value of Vub. This will constitute a first measurement of the rare Bs→K-l+nu decay by employing a modern machine learning-based algorithm to reconstruct the full Y(5S) event for the first time. |
| What you will learn: | machine learning, python programming, data analysis |
| Advisor: | Prof. Dr. Torben Ferber |
| Contact: | Dr. Pablo Goldenzweig |
| Last change: | 15.10.2024 |
| Topic: | Search for Beyond the Standard Model Higgs Bosons |
| Summary: | Together with the research groups Klute/Quast/Wolf at ETP we search for the production of two Higgs bosons within the next-to-minimal supersymmetric standard model (NMSSM). Specifically, the decays of the two Higgs bosons into a pair of tau leptons and a pair of bottom quarks are of great interest to us. This analysis offers possibilities for contributions of Master students in object reconstruction, machine learning, and interesting analysis of CMS data in general. |
| What you will learn: | BSM Higgs physics, data analysis, Python programming, C++ programming machine learning |
| Advisor: | Prof. Ulrich Husemann, Prof. Markus Klute |
| Contact: | Prof. Ulrich Husemann |
| Last change: | 29/01/2024 |
| Topic: | Search for Dark Matter in Association with Heavy Quarks |
| Summary: | Deciphering the nature of dark matter (DM) is one of the greatest scientific challenges of our time. At particle accelerators, DM can be produced and studied in a controlled laboratory environment. We are conducting a search for DM using the CMS experiment at the Large Hadron Collider (CERN), studying final states with top and bottom quarks and missing energy. In your Master's thesis, you can improve this search with the most recent CMS data and new analysis methods. |
| What you will learn: | Physics beyond the standard model, data analysis, machine learning, Python programming, C++ programming, ROOT, statistical methods and numerical optimization |
| Advisor: | Prof. Ulrich Husemann |
| Contact: | Prof. Ulrich Husemann; |
| Last change: | 26/01/2024 |
| Topic: | Machine Learning in Particle Physics |
| Summary: | Multivariate methods of data analysis have been used in particle physics for many years. Current machine learning techniques such as Convolutional Networks (CNN), Graph Neural Networks (GNNs), Normalizing Flows (NFs) and Transformers have recently also entered particle physics. Increased attention is also currently being paid to methods for the systematic investigation of machine learning techniques, collectively known as "Explainable AI/ML". Try out one of the many new possibilities this opens up in your Master's thesis. |
| What you will learn: | Collider physics, machine learning, Python programming |
| Advisor: | Prof. Ulrich Husemann |
| Contact: | Prof. Ulrich Husemann |
| Last change: | 26/01/2024 |
| Topic: | Associated ttX Production |
| Summary: | In the associated production of Higgs bosons and top quark-antiquark pairs, the top Higgs-Yukawa coupling can be directly measured. We observed this process for the first time in 2018 and have recently published updated analysis. To further understand the process and discover possible traces of new physics, we are also investigating the main background processes that look almost like the signal in the detector. These are mainly the associated production of top quarks with additional bottom quarks or Z bosons. Be part of the team investigating top-Yukawa coupling with the full data set from LHC Run 2, determining key background processes with the highest accuracy. |
| What you will learn: | Top-quark and Higgs-boson physics, data analysis, machine learning, Python programming, C++ programming, ROOT |
| Advisor: | Prof. Ulrich Husemann |
| Contact: | Prof. Ulrich Husemann |
| Last change: | 26/10/2023 |
| Topic: | B-Tagging: Identifikation von Bottom-Quark-Jets mit modernen Algorithmen |
| Summary: | Top-Quarks zerfallen fast ausschliesslich unter Abstrahlung eines W-Bosons in ein Bottom-Quark und aufgrund der hohen Masse der Bottom-Quarks koppelt auch das Higgs-Boson bevorzugt an diese. Die möglichst gute Identifizierung von b-Jets, also Jets, die aus der Hadronisierung eines Bottom-Quarks entstehen, ist daher eine zentrale Voraussetzung für Physik-Analysen im Top-Quark- oder Higgs-Boson-Bereich. Moderne Algorithmen können solche Heavy-Flavor-Jets bereits auf Trigger-Level („Level 1“ (L1) und „High Level Trigger“ (HLT)) erkennen und somit die Auswahl der für Top- und Higgs-Physik interessanten Kollisionsereignisse signifikant verbessern. Genauso wichtig wie das Funktionieren dieser Algorithmen ist auch ihre Kalibration sowie das sehr genaue Verständnis ihrer Performanz, um eventuelle systematische Einflüsse in den analysierten Datensätzen mit einbeziehen zu können. In unserer Arbeitsgruppe werden wichtige technische Beiträge zur Entwicklung und Verbesserung der Algorithmen, die von CMS zur Identifikation von b-Jets eingesetzt werden, geleistet. Interessierte können im Rahmen ihrer Bachelor- oder Masterarbeit in diesem Themenfeld mitarbeiten. |
| What you will learn: | C++- und Python-Programmierung, B-Tagging, Top- und Higgs-Physik |
| Advisor: | Prof. Dr. Thomas Müller |
| Contact: | Dr. Soureek Mitra |
| Last change: | 19.05.2022 |
| Topic: | Neue Ansätze für die Messung der Top-Quark-Masse bei CMS |
| Summary: | Auch 25 Jahre nach seiner Entdeckung am Tevatron-Beschleuniger des Fermilab in Chicago hat das Top-Quark nichts von seiner Anziehungskraft verloren. Suchen nach neuer Physik jenseits des Standardmodells der Teilchenphysik konnten bisher keine neuen Teilchen oder Wechselwirkungen finden. So rücken Präzisionsmessungen bekannter Teilchen in den Fokus, in der Hoffnung, Abweichungen zu den vorhergesagten Eingeschaften zu entdecken, die auf Beiträge neuer, bisher unbekannter Physik hinweisen. Als schwerstes derzeit bekanntes Elementarteilchen nimmt das Top-Quark eine Sonderrolle im Standardmodell ein. Es zerfällt nahezu instantan, was die Beobachtung eines quasi "nackten" Quarks ermöglicht. Die Masse des Top-Quarks ist bereits sehr genau experimentell bestimmt worden. Wir wollen die Top-Quark-Masse indirekt über die Helizität der im Top-Quark-Zerfall entstehenden W-Bosonen messen und somit eine unabhängige Massenbestimmung vornehmen. Interessierte können im Rahmen ihrer Bachelor- oder Masterarbeit an dieser Analyse mitarbeiten. |
| What you will learn: | C++- und Python-Programmierung, ROOT, Datenanalyse, Top-Physik |
| Advisor: | Prof. Dr. Thomas Müller |
| Contact: | Dr. Thorsten Chwalek, Dr. Nils Faltermann |
| Last change: | 19.05.2022 |