New Physics Search in Dijet Mass Spectrum with Compact Muon Solenoid

Abstract

Many extensions of the SM predict the existence of new massive objects that couple to quarks and gluons and result in resonances in the dijet mass spectrum. In this thesis we present a search for narrow resonances in the dijet mass spectrum using data corresponding to an integrated luminosity of 1 fb$^{-1}$ collected by the CMS experiment at the LHC, at a proton-proton collision energy of $\sqrt{s}=7$ $TeV$. %This dijet analysis is searching for new particles in the dijet mass spectrum decaying to dijets. These new particles are predicted by new physics beyond Standard Model. This thesis presents a dijet analysis performed at the Compact Muon Solenoid (CMS) in pp collisions at $\sqrt{s}=7$ $TeV$ for an integrated luminosities of 1.0 fb$^{-1}$. The dijet mass distribution of two leading jets is measured and compared to QCD predictions, simulated by PYTHIA with the CMS detector simulation. We select events which have two leading jets with $\mid \Delta\eta \mid < 1.3$ and $\mid \eta \mid < 2.5$. We fit the dijet mass spectrum with QCD parameters. Since no evidence of new physics was found, we set upper limits at 95\% CL on the resonance cross section and compare to the theoretical prediction for several models of new particles: string resonances, axigluons, colorons, excited quarks, $E_{6}$ diquarks, Randall-Sundrum gravitons, W' and Z'. We exclude at 95\% CL string resonances in the mass range $1.0 < M(S) < 4.00$ TeV, excited quarks in the mass range $1.0<2.49$ TeV, axigluons and colorons in the mass range $1.0<2.47$ TeV, $E_6$ diquarks in the mass range $1.0<3.52$ TeV, and W' bosons in the mass range $1.0<1.51$ TeV.