Top polarization measurement in single top quark production with the ATLAS detector

The top quark polarization in electroweak single top quark production allows to probe the structure of the Wtb vertex and in particular to test the left-handed vector coupling of the Standard Model and to search for anomalous right-handed and tensor couplings. This thesis reports the measurement of the single top quark polarization from the 4.7 fb−1 data recorded in 2011 by the ATLAS detector at the LHC in proton-proton collisions at the center of mass energy of 7 TeV . The polarization is extracted from angular distributions reconstructed in a specific spin basis for t-channel single top quark events. The theoretical context of the top quark production in hadron colliders via the strong and electroweak interactions is first introduced. Then the detector, the reconstruction performances of the final state physics objects as well as the selections of events having a single top quark t-channel signature are described. The unfolding and folding methods used to extract the top quark polarization are presented and tested with different configurations in the next part of the thesis. Finally, the measured polarizations are examined with their estimated systematic uncertainties coming from the theory, the detector response and modeling as well as from the statistics of the data and simulation event samples. This thesis reports the first measurement with the ATLAS detector of the single top quark polarization. The obtained results are compatible with the Standard Model predictions and will contribute to constrain the anomalous Wtb couplings.