Search for New Phenomena in Events With at Least Three Photons Collected in Pp Collisions at √ = 8 TeV With the ATLAS Detector

Abstract

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, corre- sponding to an integrated luminosity of 20.3 fb−1, were col- lected 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 (a), limits are foundtobeσ×BR(h→aa)×BR(a→γγ)2 <10−3σSM for 10 GeV < ma < 62 GeV. Limits are also presented for Higgs boson-like scalars ( H ) for m H > 125 GeV, and for a Z′decayingtothreephotonsviaZ′→a+γ→3γ.Addi- tionally, the observed limit on the branching ratio of the Z boson decay to three photons is found to be BR( Z → 3γ ) < 2.2 × 10−6, a result five times stronger than the previous result from LEP.