Abstract
A search is described for a Higgs boson decaying into two photons, one of which has an internal conversion to a muon or an electron pair (ℓℓγ). The analysis is performed using proton–proton collision data recorded with the CMS detector at the LHC at a centre-of-mass energy of 8 TeV, corresponding to an integrated luminosity of 19.7 fb−1. The events selected 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<mℓℓγ<150 GeV, and limits have been derived for the Higgs boson production cross section times branching fraction for the decay H→γ⁎γ→ℓℓγ, where the dilepton invariant mass is less than 20 GeV. For a Higgs boson with mH=125 GeV, a 95% confidence level (CL) exclusion observed (expected) limit is 6.7 (5.9−1.8+2.8) times the standard model prediction. Additionally, an upper limit at 95% CL on the branching fraction of H→(J/ψ)γ for the 125 GeV Higgs boson is set at 1.5×10−3.
Highlights
The rare decay into the γ final state of the Higgs boson is a rich source of information that can enhance our understanding of its basic properties and probe novel couplings predicted by extensions of the standard model (SM) of particle physics
As a natural extension of those analyses, the current paper describes the first search for a Higgs boson Dalitz decay, H → γ∗γ, where the γ∗ decays into a muon or an electron pair
The results presented in this paper are based on pr√oton-proton collision data recorded in 2012 with the CMS detector at a centre-of-mass energy s = 8 TeV, corresponding to an integrated luminosity of 19.7 fb−1
Summary
The rare decay into the γ final state of the Higgs boson is a rich source of information that can enhance our understanding of its basic properties and probe novel couplings predicted by extensions of the standard model (SM) of particle physics. The expected rates of the H → (Z/γ∗)γ → γ processes compared to the rate of H → γγ decay, for a Higgs boson with mass mH = 125 GeV, are [10, 11]: Γ(H → γ∗γ → eeγ) Γ(H → γγ). As a natural extension of those analyses, the current paper describes the first search for a Higgs boson Dalitz decay, H → γ∗γ, where the γ∗ decays into a muon or an electron pair. Important backgrounds include the irreducible contributions from the initial- and final-state photon radiation in Drell–Yan production, and Drell–Yan events with additional jets where a jet is misidentified as a photon. In the SM this decay occurs through two main processes: direct coupling of the Higgs boson to charm (Fig. 2a), and the usual t/W loop, where the radiated γ∗ converts to a ccin a resonant state (Fig. 2b).
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