Spin correlation and polarization of top quarks at the Run 2 of the LHC
IDPASC Portugal - PHD Programme 2016
2016 / 2017
Theoretical Particle Physics | Experimental Particle Physics
Universidade do Minho
The LHC has produced a wealth of data about top quark physics, which has allowed in-depth studies of the interactions of this particle. The data is so rich that it is now possible to probe the couplings of the top quark in great detail, looking fro deviations from Standard Model predictions - which would signal possible new physics (new particles). In the following PhD thesis proposal we study spin correlations and polarization of top quarks produced at a centre-of-mass energy of 13 TeV during the Run 2 of the Large Hadron Collider (LHC). Pair production of top quarks are studied using data collected by the ATLAS experiment. Dileptonic and semileptonic final states (corresponding to the decay of the top quarks) will be analysed and fully reconstructed using a dedicated kinematical fitter. Angular correlations and distributions which probe independent coefficient functions of the top-spin dependent parts of the top anti-top quark production spin density matrices are expected to be analised. The effects of new interactions on these observables in terms of a gauge-invariant effective Lagrangian that contains all operators relevant for hadronic top quark pair production up to mass dimension six is also explored. In particular electric and magnetic moments of top quarks are studied using angular distributions with and without full reconstruction or comparison. The study of these variables is specially relevant, since deviations in their Standard Model-espected values can be a signal, amongst many other possibilities, that the top particle is not elementar. Limits on new physics are expected to be set in addition to the measurements of top spin correlations and polarization. Dedicated analyses are to be developped to analyse the ATLAS data collected at the Run 2 of the LHC and the impact of statistical and systematic uncertainties will be studied in detail. NOTE: main supervisor is prof. António Onofre.