Measurement of the $W^{+}W^{-}$ charge asymmetry in $W \rightarrow e \nu$ events in CMS

The Standard Model (SM) of particle physics is the most general theory to describe the fundamental constituents and interactions of matter. However, precision meas- urements are needed to further test the consistency of the model or to highlight discrepancies between the theoretical predictions and the experimental results that could lead to new physics. In order to achieve this task, uncertainties connected to the modelling and simulation of the physical event must be studied. One of the main uncertainties in the simulation of a high energy proton-proton collision (such as those studied at the Large Hadron Collider) is due to the choice of the parton distribution functions (PDF). The W boson charge asymmetry is a quantity that is sensitive to the PDF set used in the Monte Carlo events generation. A precise measurement of this quantity can then discriminate between which are the best sets of PDF to be used in a future experiment and hence reduce the uncertainties on the measured quantities. In this work, data collected from the Compact Muon Solenoid experiment at CERN √ in 2012 at a centre of momentum energy of s = 8TeV are analysed alongside Monte Carlo simulations. The determination of the W boson charge asymmetry is performed exploiting events where a W boson is produced at parton level and de- cays into an electron-neutrino pair or a muon-neutrino pair. The result obtained from the experimental data is compared to Monte Carlo datasets obtained with different PDF sets. In the first chapter, a brief introduction to the Standard Model is presented with particular attention to the weak interaction. Parton distribution functions are then described from both the theoretical and the experimental point of view. The W bo- son charge asymmetry is introduced, alongside possible future high energy physics measurements. The second chapter describes the Large Hadron Collider and the Compact Muon Solenoid experiment. A detailed description of the main detectors and of the trigger system of CMS is presented alongside future physics goals. In the following chapter, the algorithms exploited to reconstruct physical objects are presented. A detailed description of reconstruction and identification for electrons and muons is reported. Reconstruction techniques for particle jets and for missing transverse energy are also illustrated. In the last chapter, the measurement of the W boson charge asymmetry is presen- ted. After the study of the selection cuts, the analysis of the background contributions to the electron sample is presented, with special attention to the determination of the Quantum Chromo-Dynamics background. Charge reconstruction efficiencies and overall reconstruction efficiencies are studied. The charge asymmetry is computed for both the electron and the muon samples separately. Finally, the comparison between the asymmetry obtained from the data and the one obtained from the Monte Carlo with different PDF sets is presented.