Search for the Higgs Boson Decays to a Photon and Two Leptons with Low Dilepton Invariant Mass

Abstract

A search for a Higgs boson decay $H\to\gamma^*\gamma\to\ell\ell\gamma$ is presented. The analysis is performed using proton-proton collision data recorded by the CMS detector at the CERN LHC at a centre-of-mass energy of 8 TeV, corresponding to an integrated luminosity of 19.7 fb$^{-1}$. The selected events have an opposite-sign muon or electron pair and a high transverse momentum photon. No excess above background has been found in the three-body invariant mass range $120<m_{\ell\ell\gamma}<150$ GeV, and limits have been derived for the Higgs boson production cross section times branching fraction for the $H\to\gamma^*\gamma\to\ell\ell\gamma$ decay, where the dilepton invariant mass is less than 20 GeV. For a Higgs boson with $m_H=125$ GeV, a $95\%$ confidence level (CL) exclusion observed (expected) limit is 6.7 ($5.9^{+.2.8}_{-1.8}$) times the standard model prediction. Additionally, a search for $H\to(J/\Psi)\gamma\to\mu\mu\gamma$ process is presented, and an upper limit at $95\%$ CL on the branching fraction of the $H\to(J/\Psi)\gamma$ decay for the 125 GeV Higgs boson is set at $1.5\times10^{-3}$.Comment: PhD dissertation, Northwestern University. 151 pages, lots of figures, some table