Search for a Massive Di-photon Resonance at sqrt{s} = 91-172 GeV

Abstract

A search for the resonant production of high mass photon pairs associated with a leptonic or hadronic system has been performed using a total data sample of 25.7 pb^-1 taken at centre-of-mass energies between 130 GeV and 172 GeV with the OPAL detector at LEP. The observed number of events is consistent with the expected number from Standard Model processes. The observed candidates are combined with search results from sqrt{s} ~ M_Z to place limits on Br(H^0 -> gamma gamma) within the Standard Model for Higgs boson masses up to 77 GeV, and on the production cross section of any scalar resonance decaying into di-photons. Upper limits on Br(H^0 -> gamma gamma) x sigma(e^+e^- -> H^0 Z^0) of 290 - 830 fb are obtained over 40 < M_H < 160 GeV. Type-I two-Higgs-doublet scalars which couple only to gauge bosons are ruled out up to a mass of 76.5 GeV at the 95% confidence level.