Search for new phenomena in events with at least three photons collected in pp collisions at $$\sqrt{s}$$ s = 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 protonproton 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 3 , 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 found to be BR(h aa) BR(a ) 2 < 10 -3 SM for 10 GeV < m a < 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 a + 3 . Additionally, the observed limit on the branching ratio of the Z boson decay to three photons is found to be BR(Z 3 ) < 2.2 10 -6 , a result five times stronger than the previous result from LEP. without whom ATLAS could not be operated efficiently.