Search for charginos and neutralinos with the ATLAS detector at the LHC

This thesis concerns the prospective study to evidence the supersymmetry with the ATLAS detector at the CERN Large Hadron Collider (LHC) by searching for the disintegration of chargino-neutralino pairs into three leptons. The analysis of this channel is performed through a rapid simulation of the detector used for the signal processing and to process the background (from the standard model and from the MSSM) which may hinder the detection. The results are given for different configurations of LHC: at low energy (√s = 9.3 TeV), at high energy (√s = 14 TeV), at low luminosity (L = 10³³ cm^-2s^-1), at high luminosity (L = 10³⁴ cm^-2s^-1). Finally, we propose an original method allowing the estimation of the gluino mass (an essential parameter of the MSSM) as well as that of all the charginos and neutralinos. This method is of course approximated but it relies on a unique experimental measurement and permits the rebuilding of the whole mass spectrum of the MSSM jauginos to be performed with a worthy precision. The experimental part of this thesis deals with the tests performed on the new photomultipliers (PMTs) HAMAMATSU R5900 which are foreseen for the outfit of the ATLAS tile calorimeter TICAL. The results of these tests show that the PMTs are in conformity with the specifications of the reading of TICAL. (author)