Measurements of the production of a W boson in association with jets and the search for Higgs pair production in the bbZ(ll)Z(jj) decay channel with the CMS detector at the LHC

Abstract

This PhD thesis presents two experimental particle physics analyses, the measurements of the production of a W boson in association with jets (W+jets) in proton-proton collisions using the muon decay channel and the search for resonant Higgs pair (diHiggs/double Higgs) production in proton-proton collisions using the bbZ(ll)Z(jj) final state. Both analyses use data recorded by the Compact Muon Solenoid (CMS) experiment at the CERN Large Hadron Collider (LHC). The W+jets analysis uses data from the proton-proton collisions at a center-of-mass energy (√s) of 8 TeV and 13 TeV collected during the LHC RunI and RunII (2015) periods, corresponding to an integrated luminosity of 19.6 fb-1 and 2.2 fb-1 respectively. The measured cross sections are reported as functions of jet multiplicity, jet transverse momenta (pT), jet pseudorapidity (η), and the scalar sum of jet transverse momenta (HT) for different jet multiplicities. Distributions of the angular correlations between the jets and the muon are examined, as well as the average number of jets as a function of HT and as a function of angular variables. The measurements are compared to the theoretical predictions from next-to(-next-to)-leading-order calculations and event simulations that utilize matrix element calculations interfaced with parton showers. The Higgs pair production analysis uses data at √s = 13 TeV collected in the LHC RunII (2016) period, corresponding to an integrated luminosity of 35.9 fb-1. The bbZZ final state considered here is the one where one Z decays into two oppositely charged leptons, and the other Z decays hadronically into two or more jets. Upper limits at 95% confidence level are placed on the production cross section of narrow-width spin-0 and spin-2 particles decaying to Higgs boson pairs. This is the first search of its kind in this final state. In addition to the analysis work, the thesis also describes the work of maintaining the conditions data and support the operation of the CMS Cathode Strip Chamber (CSC), which is the main sub-detector for measuring muons in the forward/backward regions and thus a critical detector for these analyses.