Investigation of the CP properties of VBF Higgs production in hadronic final states of H → τ τ decays with the ATLAS detector

by Serhat Ördek
Doctoral thesis
Date of Examination:2021-01-28
Date of issue:2021-02-15
Advisor:Prof. Dr. Stan Lai
Referee:Prof. Dr. Stan Lai
Referee:Prof. Dr. Arnulf Quadt
Persistent Address: http://dx.doi.org/10.53846/goediss-8436

 

 

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Abstract

English

A test of CP invariance of the VBF Higgs production process is presented in the τ τ final state. For this, a profile likelihood fit using a matrix-element observable method is employed to test whether a CP-odd component is present in the coupling. The analysis is carried out using 36.1 fb −1 of proton-proton collision data recorded at a centre-of- mass energy of 13 TeV with the ATLAS detector at the LHC. It constrains the value of the CP violation inducing parameter d ̃ to [−0.090, 0.035] at the 68% confidence level. This result is compatible with the Standard Model expectation of d ̃ = 0 and no CP violation. Particular emphasis is put on the final state including two hadronically- decaying τ leptons. Additionally, a measurement of the efficiencies of τ -lepton triggers is presented. These triggers are necessary to collect the data on which the measurement of d ̃ is based. Lastly, an ongoing measurement of Higgs-boson production cross-sections in the τ τ final state using 139 fb −1 of data is discussed, including an improved method of estimating back- ground contributions in the final state with two hadronically-decaying τ leptons.
Keywords: Higgs boson; CP violation
 
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