Searches for supersymmetric particles in leptonic final states with the ATLAS detector

This thesis presents a search for displaced leptons, a characteristic signature of long-lived particles (LLPs), using data collected by the ATLAS detector at the LHC. The analysis targets leptonic final states in proton--proton collisions from Run~2 and early Run~3, leveraging newly developed LRT-based triggers and a data-driven background estimation strategy. No significant excess over the Standard Model background is observed, and exclusion limits are set on signal model parameters such as slepton mass, lifetime for two representative supersymmetric (SUSY) scenarios. Beyond the search itself, this thesis contributes to the broader experimental toolkit for LLP detection. To enable real-time identification of displaced tracks at the High-Luminosity LHC, a Hough Transform-based algorithm is implemented on an FPGA, providing fast online pattern recognition capabilities for track triggering. Additionally, a GRU-based recurrent neural network is developed to improve prompt lepton identification, particularly at low transverse momentum, surpassing traditional cut-based methods. Together, these efforts enhance the ATLAS experiment’s sensitivity to long-lived particles and provide essential algorithmic tools for future LLP searches across a range of theoretical models.

Name thesis:degree_name

Ph.D.

Level thesis:degree_level

Dissertation

Discipline thesis:degree_discipline

Physics

Grantor

University of Illinois Urbana-Champaign

Year dc:date

2025

Author dc:creator

• Fan, Cunwei

Contributors dc:contributor

• Hooberman, Benjamin H.
• El-Khadra, Aida
• Cooper, Lance
• Noronha, Jorge

• Long-lived Particle
• Atlas
• Hough Transfrom
• Susy

Statement dc:rights

• Copyright 2025 Cunwei Fan

Language dc:language

en, eng

Handle dc:identifier

https://hdl.handle.net/2142/130095

OAI record oai:identifier

https://www.ideals.illinois.edu/oai-pmh?verb=GetRecord&metadataPrefix=etdms&identifier=oai%3Awww.ideals.illinois.edu%3A2142%2F130095