Search for heavy Majorana neutrinos in Run II and feasibility study of a track-trigger for Phase 2 with the CMS detector at the LHC

This thesis intends to present the salient anspects of the research work carried forward in collaboration with the CMS experiment group, during my PhD. The LHC accelerator and CMS detector main features are illustrated in the first chapter. The second chapter regards the CMS tracker subdetector status, performances, and future perspectives. The crucial role of the tracker in the HL(High Luminosity)-LHC era, starting from 2020, is here introduced. Once clarified the technological context and the principles of work of the machines, where the proton collisions take place, and thanks to which the particles can be revealed, a specific data anlysis of the 2015 data collected by CMS will be shown. First, the current state of the searches of new physics, focusing on heavy neutrinos and leptoquarks, is illustrated in chapter 3, where the basis for a new search are provided. An original model is proposed (chapter 4), that leads a new experimental analysis, whose strategy and results are examined in chapter 5. This is a search for physics beyond the Standard Model (SM) in the final state with two same-flavour leptons (electrons or muons) and two quarks. The analysis is performed using proton-proton collisions at √s = 13 TeV, recorded by the CMS experiment, at the CERN LHC. The data correspond to an integrated luminosity of 2.3 fb−1; the results are interpreted in the framework of a recently proposed model, in which a heavy Majorana neutrino stems from a composite scenario. The CMS collaboration is preparing the field to extend these searches in the future, at higher luminosity conditions. The HL LHC will require a totally different trigger paradigm, with the inclusion of the tracker at Level-1. After introducing the general needs and upgrade plans towards this new phase (chapter 6), a specific track-trigger proposal is formulated, based on the PCA statistical method. The software simulation and the hardware prototype of this innovative system will be discussed in chapter 7.