Search for top squark pair production in the 3-body decay mode with a single lepton final state with the ATLAS detector

Handl, David (2019): Search for top squark pair production in the 3-body decay mode with a single lepton final state with the ATLAS detector. Dissertation, LMU München: Faculty of Physics

Abstract

In this work, the results from two searches for direct pair production of top squarks, the supersymmetric partner of the top quark, are reported. Both searches focus on final states with one isolated electron or muon, multiple hadronic jets, and large missing transverse momentum. The first analysis is performed on data from proton-proton collisions delivered by the Large Hadron Collider at a centre-of-mass energy of 13 TeV and recorded by the ATLAS detector within the years 2015 and 2016, corresponding to an integrated luminosity of 36.1 fb^-1. The second analysis is performed on the full Run 2 dataset of proton-proton collisions at a centre-of-mass energy 13 TeV recorded by the ATLAS detector within the period from 2015 to 2018, corresponding to an integrated luminosity of 139 fb^-1. A particular top squark decay mode is considered, where the mass difference between the top squark and the neutralino is smaller than the top quark and as a result each top squark decays via a 3-body process into a b quark, a W boson, and a neutralino. In this phase space, the top squark pair events closely resemble top quark pair processes. No significant deviation from the predicted Standard Model background is observed in both searches. Hence, exclusion limits at 95 % confidence level on the supersymmetric model are determined. In the first analysis, top squarks with masses up to 460 GeV are excluded. With the results from the second analysis, the exclusion limit is extended and top squarks with masses up to 720 GeV and neutralino masses up to 580 GeV are excluded.

• Item Type: Theses (Dissertation, LMU Munich)
• Keywords: particle physics, supersymmetry, ATLAS detector
• Subjects: 500 Natural sciences and mathematics; 500 Natural sciences and mathematics > 530 Physics
• Faculties: Faculty of Physics
• Language: English
• Date of oral examination: 26. July 2019
• 1. Referee: Schaile, Dorothee
• Signature of the printed copy: 0001/UMC 26647