Flavour-Changing-Neutral-Currents in Top Quark Physics

Abstract

This work presents a study on top quark avour-changing-neutralcurrents (FCNC) interaction. These interactions are characterised by a vertex with a top quark and a light u or c quark, together with one of the neutral gauge bosons: gluon, photon and Z boson. They are highly suppressed in the Standard Model (SM), and are therefore a good place to search for physics beyond the SM. We start by presenting a theoretical introduction divided in three chapters. The rst one is dedicated to the subject of collider physics, where the main aspects related to the physics and mathematical background of collider experiments are discussed. A brief account of the SM is then given followed by a more detailed chapter where the subject of E ective Theories and its use in FCNC top quark physics is described. In the following chapters we rst present a study where improvement of FCNC top quark interaction limits were tested in an electronpositron collider. A post LHC scenario where no FCNC physics is found was assumed. In the next chapter we present a study on the well-known asymmetry measured in top quark pair production at the Tevatron, and its deviation in respect to the SM prediction. The study addresses the problem using a set of six dimension e ective operators in order to reproduce this asymmetry. In the following chapter a new Monte Carlo event generator, MEtop, is presented. It is a generator conceived primarily for FCNC direct top events with LO and NLO precision, but it also generates FCNC single top @ LO. The generator allows the user to generate events from three di erent sets of e ective operators. Finally, experimental simulations were performed in order to study the performance of MEtop in FCNC top quark search @ LHC.