A SEARCH FOR EVIDENCE OF PHYSICS BEYOND THE STANDARD MODEL WITH NEW LIGHT BOSONS DECAYING INTO PAIRS OF MUONS AT √S = 13 TEV USING THE CMS DETECTOR

Abstract

The standard model (SM) of particle physics is to date the most accurate description of fundamental particles and the interactions between them. While there are strong motivations for physics beyond the SM, experimental evidence has yet to be established. Searches for new light bosons can offer insight into the nature of the Higgs boson, dark matter and the possible existence of hidden sectors. New light bosons are introduced in many extensions of the SM, such as supersymmetry (SUSY) and models with hidden sectors. This dissertation presents a search for pair production of new light bosons, each of which decays into a pair of muons. Proton-proton collision data corresponding to an integrated luminosity of 35.9 fb^−1 have been collected with the Compact Muon Solenoid detector at the CERN Large Hadron Collider at a center-of-mass energy of √ s = 13 TeV. The search is uniquely sensitive to signatures with multimuon final states and is designed to be quasi model independent. The data are found to be consistent with the SM prediction. A model independent upper limit is set on the product of the production cross section, the branching fraction to dimuons squared and the acceptance as a function of the light boson mass. This limit varies between 0.15 and 0.39 fb over a light boson mass range from 0.25 to 8.5 GeV. The limit is interpreted in the context of the next-to-minimal supersymmetric SM and a minimal SUSY model with a U(1)vD hidden sector that allows for nonnegligible light boson lifetimes. More stringent limits are set for both scenarios compared to earlier studies conducted on proton-proton collision data at √ s = 8 TeV by CMS