Results of analysis of the effective mass spectra of photon pairs produced in dC, dCu and pC interactions at momenta of 2.75, 3.83 and 5.5 GeV/c per nucleon, respectively, are presented. A structure at effective mass of about 38 MeV/c2 is observed. The results of testing the observed signal are presented. The test results support the conclusion that the observed signal is the consequence of detection of a particle with a mass of about 38 MeV/c2 decaying into a pair of photons.

Abstract. The results of experiments on photon and π 0 pairs production in interactions of 5.5 GeV/c protons, 2.75 and 3.83 GeV/c per nucleon deuterons with carbon and copper nuclei are presented. As previously reported (see.[1] and references therein), along with π 0 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. Here are some results of testing the signal and results of statistical analysis of the experimental data which allow to explain the lack of appearance of the signal in other experiments [2,3] and make predictions for possible appearances of the signal in upcoming experiments.

A new resonance structure at M = 355 ± 6 ± 9 MeV is observed in the invariant mass spectrum of two γ-quanta produced in the reaction d + C → γ + γ + x at momentum 2.75 GeV/c per nucleon. Preliminary estimates of its width and cross section are Γ = 41 ± 12 MeV and σ γγ ∼ 0.6 µb. The collected statistics is 2680 ± 310 events of 1.5 · 10 6 triggered interactions of a total number 3 · 10 12 dC-interactions.