Measurement of the top quark mass in topologies enhanced with single top quarks produced in the t-channel using flavour tagging and a neural network with ATLAS data at √s = 8TeV

Abstract

In this thesis a measurement of the top quark mass in topologies that have been enhanced with single-top quark decays in the t-channel produced via weak interactions is presented. The dataset consists of proton-proton collisions at a centre-of-mass energy of sqrt(s) = 8 TeV collected with the ATLAS detector at the LHC with a total integrated luminosity of L = 20.3 1/fb. Selected events contain exactly one charged lepton - which can be either an electron or a muon -, missing transverse energy and two jets with exactly one of the two being b-tagged. The techniques of b-tagging used to identify jets induced by heavy quarks is explained further. In addition, the signal is enhanced using a neural network based discriminant that combines the ability to discriminate between signal and background of several correlated variables. To determine the mass of the top quark a template method is used in combination with the mass sensitive variable, m(l b), which is the invariant mass of the lepton and the b-tagged jet. The top quark mass is measured as m(top) = [172.2 +/- 0.7 (stat.) +/- 1.9 (syst.)] GeV.