Search for anomalous production of high mass photon pairs in e+e− collisions at LEP

A search for events with photon pairs of large invariant mass is described based on a data sample of 43 pb−1 collected with the OPAL detector. This search is motivated by the L3 observation of four events of the type e+e− → l+l−γγ with an invariant mass of the two photons, mγγ, clustering around 60 GeV. In the OPAL data, four ℓ+ℓ−γγ events are found with mγγ above 40 GeV. The number of observed events is consistent with the QED expectation and no obvious resonance structure is seen. Three candidate qq̄γγ events with mγγ above 40 GeV are found and no νν̄nγγ candidate with mγγ > 5 GeV is found. From these searches an upper limit is set on any anomalous production of ℓ+ℓ−γγ (ℓ = e, μ, τ) events, where the ℓ+ℓ− pair comes from a virtual Z0 and mγγ is near 60 GeV , of B(Z0 → Z∗0γγ → ℓ+ℓ−γγ) < 6.0 × 10−7 at the 95% CL. In a similar search in the reaction e+e− → γγγ, seven events are observed with a photon pairing of mass near 60 GeV compared to an expected background of 2.7 ± 0.4 from QED. In a search for the production of a 60 GeV resonance X in two-photon collisions, an upper limit is set on ΓXB2(X → γγ) of 2.6 MeV at the 95% CL. A search is also performed for ℓ+ℓ−X (ℓ = e, μ) events in non-γγ decay modes of X. No indication of a 60 GeV resonance is seen. Combining these two searches, ΓX values greater than 110 MeV are excluded at the 95% CL for ℓ+ℓ−γγ (ℓ = e, μ) cross-sections greater than 0.05 pb.