# Detector control systems and searches for leptonic decays of the Higgs Boson in the ATLAS Experiment at the LHC

Turner, Russell (2020). Detector control systems and searches for leptonic decays of the Higgs Boson in the ATLAS Experiment at the LHC. University of Birmingham. Ph.D.

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## Abstract

The Large Hadron Collider at CERN has recently finished Run-II, during whichproton beams were collided at a centre of mass energy of 13 TeV, producing data equivalent to a total integrated luminosity of 139 fb^{−1} for the ATLAS experiment. The collider and its experiments have now entered into a shutdown period, in which various components will be upgraded to accommodate for a higher luminosity (300 fb^{−1} expected) run (Run-III). This thesis presents the development of a control and monitoring system for the upgrade to the ATLAS level one calorimeter trigger. This system is designed for use in the ATLAS control room, and so needs to be easily understood and used by shifters who are not necessarily experts of the trigger system.
Also presented in this thesis are two analyses related to searches for the decays of the Higgs boson to lepton-antilepton final states by the ATLAS experiment. The first of these analyses is an analysis of the prospects of measuring the H → µ^+µ^− decay channel during the high luminosity phase of the LHC, Run-IV. During this run, ATLAS is expected to collect a total of 3000 fb^{−1} worth of data at a centre of
mass energy of 14 TeV. This prospects analysis finds an expectation of measuring the decay with a significance of 9.6σ and a fractional precision on the branching ratio of 13% assuming the standard model decay rate.
The second analysis is a search for the H → e^+e^− decay channel using the entire ATLAS dataset from Run-II. No significant excess of events is observed and a 95% CL_S upper limit on the branching ratio B(H → e^+e^−) of 3.6 \times 10^{−4} is set, approximately a factor of 5 lower than the previously observed limit. This limit is four orders of magnitude larger than the standard model value of the branching ratio, 5 \times 10^{−9}, and is compatible with the expected limit of 3.5 \times 10^{−4}.

Type of Work: Thesis (Doctorates > Ph.D.)
Award Type: Doctorates > Ph.D.
Supervisor(s):
Supervisor(s)EmailORCID
Thompson, PaulUNSPECIFIEDUNSPECIFIED