Search for New Light Bosons in Higgs Boson Decays

Abstract

The Standard Model (SM) of particle physics is a theory that summarizes our current knowledge about the most fundamental constituents of matter and interactions between them. The Higgs boson is a central part of the SM as it provides masses to all other particles. After many decades of searches for it, on the 4th of July 2012 CERN announced a discovery of a new particle by CMS and ATLAS collaborations at the Large Hadron Collider (LHC). The properties of the new particle and the properties of the Higgs boson predicted by the SM are consistent at the level of precision of current measurements. The extensive physics program of the LHC experiments includes searches for new physics beyond the SM which complement further precision measurements of the properties of the new particle. These searches may lead to earlier confirmation that the particle is not the SM Higgs boson in case the new physics is found. This dissertation is dedicated to a search for decays of the newly discovered particle to pairs of new light bosons, each of which decays into the μ+μ- final state. The data set corresponds to an integrated luminosity of 5.3 fb^-1 of proton-proton collisions at √s = 7 TeV, recorded by the CMS experiment at the LHC in 2011. No excess of events above the SM predictions is observed. A model-independent upper limit of 0.86 fb on the product of the cross section times branching fraction times acceptance is set. The obtained limit is applicable to models where the new light bosons have lifetimes corresponding to flight distances within a few cm from the proton beamline before their decay. The recipe for application of the results to an arbitrary model with the same final state is provided. Interpretation of the results in the context of two benchmark models significantly surpasses the sensitivity of previous similar searches.