Étude de la production de paires de bosons Z à grande masse invariante dans des collisions proton-proton à √ s = 8 TeV auprès de l’expérience CMS

In this Master Thesis, we study the Z boson pair production in proton-proton collisions at 8 TeV in the center-of-mass collision frame, from the data collected in 2012 by the CMS experiment. This study is performed in the final states containing two electron-antielectron or muon-antimuon pairs. Our goals are to compute the cross section of the process, and to study the electroweak corrections applied to it. These electroweak corrections have only recently been computed, and are for the first time compared with experimental data in these final states. We first identify the sub-processes, at different orders in αS, contributing to the Z boson pair production in simulated samples from specific generators and we compare these contributions to the published results. We then introduce a parameterization of these electroweak corrections to the dominant sub-process qq¯ → ZZ and compare the distributions to the compared results. We compare the data and the Monte-Carlo simulations, corrected for NLO electroweak effects, after having applied the necessary cuts in order to isolate the process of interest. After verifying the CMS trigger efficiency, we develop and implement a background estimation method, essentially based on the data samples. We conclude from this background study that the latter can be neglected in the adjustment, and simply substracted for the cross section determination. The comparison between data and simulations leads to the conclusion that the simulated distributions with or without electroweak corrections are both compatible with the data. Finally, we determine the Z boson pair production cross section, imposing that for each Z boson |MZ − 91, 2 GeV| < 30 GeV, and that the invariant mass of the two Z bosons system is greater than 200 GeV. This cross section is measured to be (5.76 ± 0.68) pb, in agreement with published results.