Angular Distributions in t-channel Single-top Quark Decay

The Standard Model is by far the most theory describing physics phenomena, nevertheless there are still observations that does not match SM predictions, for example the large matter-antimatter asymmetry in the universe, which hint at physics beyond the Standard Model. The top quark, which is the heaviest among all fundamental particles in the SM, is the most experimentally relevant probe to BSM Physics. In SM, top quarks can be produced by charged-current electroweak interaction through the Wtb vertex, which leads to a high degree of polarization of top quarks produced. In this thesis, angular distribution of decay products in single top quark t-channel events are used to determine the three components of polarization vector of the top quark ensemble and anti-top quark ensemble. After establishing a significant polarization beyond 0, an on-going analysis aims to use the quadruple differential decay rate of the same set of events to simultaneously determine limits on 6 EFT coefficients. Both analyses are based on pp collision data with $\sqrt{s}$ = 13 TeV at the LHC collected by the ATLAS detector, with an integrated luminosity of 139.0 fb^-1.