Reconstruction des électrons et recherche de couplages anormaux dans le canal pp->ZZ->4l avec le détecteur CMS auprès du LHC

I did my PhD in Particle Physics with the CMS (Compact Muon Solenoid) team from Laboratoire Leprince-Ringuet at Ecole Polytechnique. The subjects of my study are the pp→ZZ+X production and the search for anomalous triple gauge couplings (ATGCs) using the data collected by the CMS detector at LHC at sqrt{s}=7 TeV. This work began with the first collisions at the LHC in the end of 2009 with the study and optimisation of electron reconstruction algorithms. Selection criteria of pure electrons samples from Z decays have been studied. The electron reconstruction efficiency has been measured on 2010 and 2011 data and the results have been used by the CMS collaboration for the 2010 and 2011 analyses. Then I dealt with the analysis of ZZ→4l channel and the search for anomalous triple gauge couplings, as possible signature of new physics. A recovery algorithm to correct the 4-leptons mass from Final State Radiations loss has been developed: 4.2% of ZZ→4μ events are corrected with an FSR selection purity of 95.6%. Then search and limits extraction of ATGCs have been done. Neutral trilinear couplings are forbidden in Standard Model but can be introduced using an effective Lagrangian with new couplings terms f4Z and f5Z in the ZZZ case. ATGCs generally generate an increase of the ZZ cross section production and some distortions in the ZZ mass spectrum or Z kinematical distributions. Thus a pure selection of ZZ→4l events has been established and kinematical distributions have been studied. I have performed a search for ATGCs thanks to a reponderation method. Using the shape of the invariant mass of the 4-leptons system, limits on ZZZ ATGCs are set at 95% confidence level: -0.0116< f4Z <0.0116 et -0.0119< f5Z <0.0119.