Search for heavy neutral gauge boson Z using CMS detector at the LHC

Abstract

The Standard Model of particle physics is a well-established framework which describes the nature of the matter in the universe and the way this matter interacts with each other. Though it is a well-tested framework and acts as a fundamental theory till now, it fails to describe various physics phenomena such as the existence of dark matter and dark energy in the universe, matter-antimatter asymmetry in the universe, prediction of neutrino masses and prediction of force carrier for the fourth fundamental force i.e. the gravitational force. To address these questions, many theories beyond the standard model have evolved with time such as the Grand Unified Theories, Supersymmetry, and String theory. These theories predict new gauge fields and interactions. A common manifestation of these new gauge fields and interactions is particles with TeV scale masses. One such particle is the heavy neutral spin-1 gauge boson, Z , which arises from extensions of the electroweak symmetry of the standard model. The recent results from these Z searches have eluded the discovery thus far. These searches have assumed the production of Z via Drell-Yan process at the LHC with sizable coupling to light quarks. To complement these searches, a new search for Z boson produced via vector boson fusion (VBF) processes is presented. The first results of the search for Z through VBF processes at the LHC, using proton-proton collision data at the center-of-mass energy of 13 TeV collected by the CMS detector are reported. No significant excess is observed in the data. The Z is observed to be excluded below mass 1.72 TeV with 20% branching fraction in case of universal coupling to light and heavy fermions and observed to be excluded below 1.77 TeV in the case of enhanced coupling to heavy fermions. Besides this, the assembly and characterization of the Gas Electron Multiplier detectors as part of CMS muon system upgrade, performed at Panjab University, Chandigarh is also presented.