Resonance structure in the γγ invariant mass spectrum in pC- and dC-interactions

Along with π⁰ and η mesons, a resonance structure in the invariant mass spectrum of two photons at M _γγ = 360 ± 7 ± 9 MeV is observed in the reaction dC → γ + γ + X at momentum 2.75 GeV/c per nucleon. Estimates of its width and production cross section are Γ = 63.7 ± 17.8 MeV and σ_γγ = 98 ± 24⁺⁹³₋₆₇ μb, respectively. The collected statistics amount to 2339 ± 340 events of 1.5 × 10⁶ triggered interactions of a total number ∼1012 of dC-interactions. This resonance structure is not observed in pC collisions at the beam momentum 5.5 GeV/c. Possible mechanisms of this ABC-like effect are discussed.