Abstract
A search for the Higgs boson decaying into a photon and a pair of electrons or muons with an invariant mass mℓℓ<30 GeV is presented. The analysis is performed using 139 fb−1 of proton–proton collision data, produced by the LHC at a centre-of-mass energy of 13 TeV and collected by the ATLAS experiment. Evidence for the H→ℓℓγ process is found with a significance of 3.2 over the background-only hypothesis, compared to an expected significance of 2.1 for the Standard Model prediction. The best-fit value of the signal-strength parameter, defined as the ratio of the observed signal yield to the one expected in the Standard Model, is μ=1.5±0.5. The Higgs boson production cross-section times the H→ℓℓγ branching ratio for mℓℓ<30 GeV is determined to be 8.7−2.7+2.8 fb.
Highlights
In July 2012, the ATLAS and CMS Collaborations at the CERNLarge Hadron Collider (LHC) announced the discovery of a new particle with a mass of approximately 125 GeV [1,2]
This paper describes a search for H → eeγ and H → μμγ decays with m < 30 GeV
These are based on events generated using the Sherpa 2.2.8 configuration described above with object efficiencies approximated by parameterisations rather than using the full ATLAS detector simulation and reconstruction software
Summary
Large Hadron Collider (LHC) announced the discovery of a new particle with a mass of approximately 125 GeV [1,2]. Multiple processes contribute to the H → γ decay: Dalitz decays involving a Z boson or a virtual photon (γ ∗) (Fig. 1(a–c)), as well as the decay of the Higgs boson to two leptons and a photon from final-state radiation (FSR) (Fig. 1(d)) Their respective fractions depend on the invariant mass of the dilepton pair, m. √ Based s = 13 on a data sample of proton–proton (pp) collisions at TeV with an integrated luminosity of 35.9 fb−1, the CMS Collaboration reported a 95% CL upper limit on the production cross-section times branching ratio for the low-mμμ H → μμγ process of 4.0 times the SM prediction [13] Both the ATLAS and CMS Collaborations carried out searches at. The signal yield is extracted by a simultaneous fit of parametric functions to the reconstructed γ invariant mass (m γ ) distributions in all categories
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