CERN Accelerating science

Thesis
Report number CERN-THESIS-2024-259
Title Searching for new physics using the ATLAS and FASER detectors
Author(s) Theiner, Ondrej (U. Geneva (main))
Publication 2024 - 213.
Thesis note PhD : U. Geneva (main) : 2024
Thesis supervisor(s) Sfyrla, Anna
Note Presented 31 Oct 2024
Subject category Particle Physics - Experiment ; Detectors and Experimental Techniques
Accelerator/Facility, Experiment CERN LHC ; ATLAS
CERN LHC ; FASER
Abstract Some cosmological observations and data from particle physics experiments suggest that the Standard Model (SM) of particle physics is not a complete theory. Phenomena such as dark matter, dark energy, and the matter-antimatter asymmetry could be explained by the existence of new particles that are heavier than the top quark, the heaviest known elementary particle, or by particles that do not directly interact with ordinary matter in the Universe and are therefore invisible. Supersymmetry (SUSY) is one extension of the Standard Model that could explain some of these phenomena by introducing a new symmetry between bosons and fermions and adding new particles to those described by the Standard Model. However, SUSY is not the only viable theory. There is a whole new class of hypothetical particles that are much lighter, with masses in the MeV to GeV range, which could produce dark matter with the correct relic density. In recent decades, searches for new physics have been conducted at the TeV energy frontier. The ATLAS and FASER experiments at the CERN Large Hadron Collider (LHC) search for new physics potentially generated by proton-proton collisions at a center-of-mass energy of 13–14 TeV, employing two different approaches. ATLAS focuses on regions with high transverse momentum of collision products in the central area of the detector. In contrast, the FASER experiment, located 480 meters from the ATLAS collision point, searches for long-lived, weakly interacting particles produced in the very forward direction. This thesis is divided into three main parts. The first part provides an introduction to the challenging field of collider physics with an emphasis on searches for new physics. The second part is focused on the ATLAS experiment. The third part concerns the FASER experiment. The ATLAS detector records proton-proton collision data at approximately 40 MHz, making an efficient trigger and data acquisition system crucial for optimal operation and physics performance. This efficiency is vital for the sensitivity to processes that may indicate new physics. This part details the optimization of the track extrapolation algorithm used for Particle Flow jet reconstruction at the High-Level Trigger and explores searches for new physics. It introduces the search for the pair production of higgsinos decaying into a final state with multiple b-quarks and missing transverse momentum. Additionally, it presents new results from the reinterpretation of this search in the context of other intriguing new physics models: one related to supersymmetry and another to a dark sector extension of the Standard Model. The part of the thesis dedicated to the FASER experiment describes the development of the detector's trigger and data acquisition system, followed by the subsequent commissioning and operational activities of the experiment.
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Corresponding record in: Inspire
Email contact: ondrej.theiner@cern.ch

 Δημιουργία εγγραφής 2024-12-10, τελευταία τροποποίηση 2024-12-20


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