Study of Triple-GEM detectors for the CMS muon spectrometer upgrade at LHC and study of the forward-backward charge asymmetry for the search of extra neutral gauge bosons

This PhD thesis takes place in the CMS experiment at CERN’s Large Hadron Collider (LHC). The LHC allowed the discovery of the Brout-Englert-Higgs boson in 2012, and is designed to run for at least 20 years, with an increasing luminosity that will reach by 2025 a value of 7.5 · 1034 cm−2 s −1 , that is a yield five times greater than the one initially intended. As a consequence, the experiments must adapt and upgrade many of their components and particle detectors. One of the foreseen upgrades of the CMS experiment concerns the Triple Gas Electron Multiplier (GEM) detectors, currently in development for the forward muon spectrometer. These detectors will be installed in CMS during the second long LHC shutdown (LS2), in 2018-2019. The aim of this upgrade is to better control the event trigger rate at Level 1 for muon detection, thanks to the high performance of these Triple GEM detectors, in presence of very high particle rates (> 1 kHz/cm2 ). Moreover, thanks to its excellent spatial resolution (∼ 250 µm), the GEM technology can improve the muon track reconstruction and the identification capability of the forward detector. The goal of my research is to estimate the sensitivity of Triple GEMs to the hostile background radiation in CMS, essentially made of neutron and photons generated by the interaction between the particles and CMS detectors. The accurate evaluation of this sensitivity is very important, as an underestimation could have ruinous effects of the Triple GEMs efficiency, once they are installed in CMS. To validate my simulations, I have reproduced experimental results obtained with similar detectors already installed in CMS, such as the Resistive Plate Chambers (RPC). The second part of my work regards the study of the CMS experiment capability to discriminate between different models of new physics predicting the existence of neutral vector bosons called Z 0 . These models belong to plausible extensions of the Standard Model. In particular, the analysis is focused on simulated samples in which the Z 0 decays in two muons, and on the impact that the Triple GEM detectors upgrades will bring to these measurements during the high luminosity phase of the LHC, called Phase II. My simulations prove that more than 20% of the simulated events see at least one muon in the CMS pseudo-rapidity (η) region covered by Triple GEM detectors. Preliminary results show that, in the case of 3 TeV/c2 models, vii it will be possible already at the end of Phase I to discriminate a Z 0 I from a Z 0 SSM with a significance level α > 3σ.