Study of the modelling of top quark events with the CMS experiment

At elementary particle level, the standard model (SM) provides a description for all of the fundamental interactions, except for gravity. Up to now the SM has been successfully tested but unfortunately it does not describe all of the observed phenomena and is only valid for interactions up to the TeV scale. To provide new insights in physics beyond the TeV scale and search for new physics phenomena, the LHC was built, colliding protons at centre of mass energies of 7 and 8 TeV. To study the interactions at the LHC physicists use large detectors like the Compact Muon Solenoid (CMS) experiment. Due to the high energy of the collisions, top quarks will be produced at a very high rate. In this thesis, a study of the modelling of these top quarks is performed us- ing the reconstructed top quark mass. Events are selected corresponding to the semimuonic decay channel of tt¯ events, at an interaction energy of √s = 8 TeV. The top quark mass is estimated as a function of cuts on the transverse momen- tum, pT , of the jet constituents where-after the jets are reclustered. As a result, the estimated top quark mass changes for each applied threshold. The slope of the top quark mass evolution is determined as the difference of the top quark mass estimation for two different pT thresholds applied on the constituents. This slope is obtained for each simulated model and the data. We found that none of tt¯ simulated samples models correctly the slope of the data because the transverse momentum distribution of the jet constituents is not accurately modelled.