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 $\sqrt{s} = 8\,\mathrm{TeV}$

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 $\sqrt{s}=8\,\mathrm{TeV}$ collected with the ATLAS detector at the LHC with a total integrated luminosity of $\mathcal{L}_{\mathrm{int}} =20.3\,\mathrm{fb^{-1}}$. 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, $m(\ell b)$, which is the invariant mass of the lepton and the $b$-tagged jet. The top quark mass is measured as $m_{\mathrm{top}} = [172.2 \pm 0.7\,(\mathrm{stat.}) \pm 1.9\,(\mathrm{syst.})]\,\mathrm{GeV}$.