Measurement of top quark and W boson polarisation observables with t-channel single-top-quark events in the ATLAS experiment.

This thesis presents two studies, one related with the alignment of the ATLAS Inner Detector tracking system and other with the measurement of top quark and W boson polarisation observables using t-channel single-top-quark events. The first topic describes the implementation of a monitoring tool, which is used to monitor the Level 1 alignment corrections obtained in the calibration loop, as well as the use of constraints on the momentum and impact parameters biases using $Z \rightarrow\mu\mu$ events on the alignment algorithms. These techniques were developed during 2012 data taking campaign and provide the most accurate description of the ATLAS Inner Detector. The second topic presents a detailed measurement of top quark and W boson polarisation observables using the 20.3 $fb^{-1}$ of data collected by the ATLAS detector at $\sqrt{s}$ = 8 TeV. The measurement is performed using $t$-channel single top quark events and exploits the feature that the produced top quark is highly polarised along the direction of the spectator-quark. This feature allows the construction of different frames where different angular distributions of the decay products of the top quark can be measured. These angular distributions are distorted by detector and efficiency effects which are corrected by an unfolding method based on Bayes theorem. This thesis presents the measurement of the top quark polarisation observable $\alpha_lP$, the normal and transverse W boson polarisation asymmetries, the $A_{FB}^N$ being sensitive to the imaginary part of the Wtb anomalous coupling $g_R$, and the W boson helicity fractions.