Identification of the tau leptons decaying hadronically and search for supersymmetric particles decaying to tau leptons with the CMS detector at LHC

This work is dedicated to the search of supersymmetric processes in simulated data of proton-proton collisions. The search is limited to processes in which tau leptons are produced and we have focused on the reconstruction of the hadronic decay of these tau leptons. The main difficulty of this work has been to reconstruct the jets of particles generated in tau decay and to differentiate them from the jets issued in quark or gluon fragmentation. The standard model and the interaction of elementary particles are presented in the first chapter. The LHC (large hadron collider) and the CMS (compact muon solenoid) are described in the second chapter. The third chapter focuses on the reconstruction tools and the identification of the hadronic jets of tau. Particularly a reconstruction method of photons and neutral pions contained in the jets is introduced. This method relies on the trajectograph and the electromagnetic calorimeter of CMS. In the fourth and fifth chapters we detail and compare events from supersymmetric processes with those stemming from the standard model. We look for supersymmetric events in which the 3 following conditions appear: 1) 2 lepton tau with opposed charges, 2) a high value of the missing transverse energy, and 3) at least 2 jets with big impulse generated in the fragmentation of one quark. In the last chapter 2 different methods used to detect events different from those stemming from the standard model are detailed. In both cases the level of significance of the results is greater than 5: such events have been detected. (A.C.)