Resonance Structure in the $\gamma\gamma$ Invariant Mass Spectrum in   $p$C- and $d$C-Interactions
  Along with $\pi^0$ and $\eta$ mesons, a resonance structure in the invariant mass spectrum of two photons at $M_{\gamma\gamma}= 360 \pm 7 \pm 9$ MeV is observed in the reaction $d C\to\gamma + \gamma +X$ at momentum 2.75 GeV/c per nucleon. Estimates of its width and production cross section are $\Gamma = 63.7 \pm 17.8$ MeV and $\sigma_{\gamma\gamma}=98\pm24^{+93}_{-67} {\rm \mu b}$, respectively. The collected statistics amount to $2339 \pm 340$ events of $1.5\cdot 10^6$ triggered interactions of a total number $\sim 10^{12}$ of $d$C-interactions. This resonance structure is not observed in $p$C collisions at the beam momentum 5.5 GeV/c. Possible mechanisms of this ABC-like effect are discussed. 
Kh. U. Abraamyan (1 and 3), M. I. Baznat (2), A. V. Friesen (1), K. K.   Gudima (2), M. A. Kozhin (1), S. A. Lebedev (1 and ...