This thesis presents a new method to measure tau lepton universality in W boson decays at the LHC. Ratios of lÏ had and eÎ¼ final states are compared in ttÌ and Z â Ï + Ï â decays, with l representing either a muon or electron, and Ï had is a tau lepton which decays hadronically. The double-ratio cancels uncertainties from Ï had lepton identification, which can be large at hadron colliders, and enables a precision test of tau lepton universality at the level of â¼ 1.5%. This method is applied to data collected by the ATLAS experiment during 2015â2018 data taking at s = 13 TeV, and indicates that lepton universality can be tested with ATLAS data at a precision of 1.6%. However there still remain differences between the expected Z â Ï + Ï â yields of the nominal and systematic signal simulation samples. These differences need to be understood before a precise measurement of lepton universality can be performed. In addition, a calibration of the Ï had lepton identification methods used by the ATLAS experiment during 2015â2018 data taking at s = 13 TeV is presented. The efficiency of the Ï had identification is measured in both data and simulation, and the resulting differences between the efficiency measurements are used to correct the efficiency in simulation to the observations in data.
|Date of Award||1 Aug 2021|
- The University of Manchester
|Supervisor||Terence Wyatt (Supervisor) & Alexander Oh (Supervisor)|