Thesis

Development of the MEtop generator

• Call:

  IDPASC Portugal - PHD Programme 2015

• Academic Year:

  2015 / 2016

• Domains:

  Theoretical Particle Physics | Experimental Particle Physics

• Supervisor:

  Rui Santos

• Co-Supervisor:

  Nuno Castro

• Institution:

  Faculdade de Ciências - Universidade de Lisboa

• Host Institution:

  Centro de Física Teórica e Computacional da FCUL and LIP

• Abstract:

  The top is the least known of all quarks and the ideal place to look for new physics. In fact, unlike all other quarks, the top decays before hadronisation occurs. A huge number of tops have already been produced during the 7 and 8 TeV runs. This number will be much larger when the LHC resumes operation with energies of 13/14 TeV. Therefore, we expect to understand in more detail if the top quark is just like the other quarks but with a larger mass or if it hides new physics. The goal is to search for new physics with an improved version of the MEtop generator. MEtop is a generator build to study single top quark production via flavour-changing neutral currents (FCNC). MEtop’s present version allows for Next-to-Leading-Order direct top production pp→t and Leading-Order production of several other single top processes. A few packages with definite sets of dimension six operators are available. MEtop is now an official generator of CERN's ATLAS collaboration. We plan to improve the generator in order to optimize searches of new physics that could be hiding in FCNC top physics at the LHC. As it is based on an effective Lagrangian approach where the symmetries of the Standard Model (SM) are present, any sign of new physics will reflect itself in other physical processes due to gauge invariance. Therefore this generator will enable us to identify the origin of new physics related to the top. The core of the work will be to look at existing observables, design new ones, and also understand how higher order corrections affects the observables. In more detail we plan to i) use observables such as top polarization to reduce the background as well as explore the structure of the Wtb vertex in some of the processes with top quarks in the final states. This will increase the sensitivity to new physics; ii) use the same observables to distinguish between the contributions of the different dimension six operators; iii) understand how the observables are affected by higher order QCD corrections. One of the important points to address is how the Initial State Radiation can be effectively taken into account; iv) look for new observables that can be used in FCNC top studies and more general effective operators studies; v) include other final states in the generator like top + photon, top + heavy flavor and top + Z.​​