Search for New Phenomena in Events with at Least Three Photons Collected in pp Collisions at √s̅ = 8 TeV with the ATLAS Detector
AbouZeid, O. S.
Izen, Joseph M.
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Results of a search for new phenomena in events with at least three photons are reported. Data from proton–proton collisions at a centre-of-mass energy of 8 TeV, corresponding to an integrated luminosity of 20.3 fb⁻¹, were collected with the ATLAS detector at the LHC. The observed data are well described by the Standard Model. Limits at the 95 % confidence level on new phenomena are presented based on the rate of events in an inclusive signal region and a restricted signal region targeting the rare decay Z → 3γ, as well as di-photon and tri-photon resonance searches. For a Standard Model Higgs boson decaying to four photons via a pair of intermediate pseudoscalar particles (α), limits are found to be σ x BR (h → αα) x BR (α → γγ)² < 10⁻³σ_SM for 10 GeV < m_α < 62 GeV. Limits are also presented for Higgs boson-like scalars (H) for m_H > 125 GeV, and for a Z′ decaying to three photons via Z′ → α+γ → 3γ. Additionally, the observed limit on the branching ratio of the Z boson decay to three photons is found to be BR (Z → 3γ) < 2.2 x 10⁻⁶, a result five times stronger than the previous result from LEP.