Probing the Higgs coupling to the top quark at the LHC in the CMS experiment

This thesis reports a study of the Higgs boson production in association with top quarks√and decaying into τ leptons in proton-proton (pp) collisions at s = 13 TeV recorded withthe CMS detector at the CERN Large Hadron Collider (LHC).This work has been carried out in the context of the Run 2 of the LHC, marked byan increase in the center-of-mass energy from 8 to 13 TeV together with an increase inthe instantaneous luminosity of the collisions with respect to Run 1. To cope with thisnew data-taking conditions, CMS had initiated a full upgrade of the Level-1 trigger systemachieved by 2016. This new system and in particular the new Level-1 electron and photonalgorithm have successfully contributed to a large number of CMS results using Run 2data. The commissioning of this new system and its performance measured in the firstdata collected with this new trigger are presented in details.An original analysis technique based on the Matrix Element Method optimized for the¯search of the ttH, H → τ τ process is also presented, including several generic tools whichcan be used in a large variety of H → τ τ analyses. Results of the CMS analysis usingthis method based on 35.9 fb−1 collected in 2016 are presented. The background-onlyhypothesis is disfavored but not yet excluded by this analysis alone.This thesis reports a study of the Higgs boson production in association with top quarks and decaying into τ leptons in√proton-proton (pp) collisions at a center-of-mass energy of s = 13 TeV recorded with the CMS detector at the CERNLarge Hadron Collider (LHC).This work has been carried out in the context of the Run 2 of the LHC, marked by an increase in the center-of-mass energyfrom 8 to 13 TeV together with an increase in the instantaneous luminosity of the collisions with respect to Run 1. To copewith this new data-taking conditions, CMS had initiated a full upgrade of the Level-1 trigger system achieved by 2016.This new system and in particular the new Level-1 electron and photon algorithm have successfully contributed to a largenumber of CMS results using Run 2 data. The commissioning of this new system and its performance measured with thefirst data collected with this new trigger are presented in details.¯A novel analysis technique based on the Matrix Element Method optimized for the search of the ttH, H → τ τ process isalso presented, including several generic tools which can be used in a large variety of H → τ τ analyses. Results of the CMSanalysis using this method based on 35.9 fb−1 collected in 2016 are presented. The background-only hypothesis is disfavoredbut not yet excluded by this analysis alone.