Measurement of the inclusive photon production cross section and study of associated W-photon production in proton-proton collisions at the LHC

The Large Hadron Collider (LHC) at CERN Geneva is presently colliding beams of protons at a centreof-mass energy of 7 TeV. Operations started at the end of 2009 and it is expected to accumulate a totalintegrated luminosity of 1 fb−1 by the end of 2011, opening the first window on the Physics of fundamentalinteractions at the TeV scale. The Compact Muon Solenoid (CMS) is a general-purpose detector currentlyoperating at the LHC. The CMS Electromagnetic Calorimeter (ECAL) has been designed to achieve excellent energy and position resolution for electron and photons and is composed by 76000 PbWO4 crystals.This thesis describes the original contributions of the author to the preparation of the CMS experimentand analysis of the first collision data.The trigger and data acquisition software of the CMS ECAL is presented and its performance discussed,as well as the performance of the ECAL detector and trigger system.√The first results on the measurement of the inclusive isolated photon production cross section at s =−17 TeV using 2.9 pb of pp collisions are presented. Finally, a study of the CMS sensitivity to W-photonproduction is presented and perspectives for the total and differential cross-section measurements withearly LHC data are discussed.