Search for resonances in the mass spectrum of two-photon events produced in $\pi^{+}A$-interactions in the hyperon-M experiment at the U-70 accelerator complex

Studies at the Nuclotron in JINR indicate the presence of a previously unknown resonance-like structure in the two-photon mass spectrum in the region of $300$–$400$ MeV/c$2^\circ$, observed in nucleus–nucleus interactions. The goal of this work is to search for such structures in the two-photon mass spectrum in meson–nuclear interactions at a momentum of $7$ GeV/c at the Hyperon-M experiment of the U-70 accelerator complex. An upper limit has been established on the ratio of the cross section for the formation of unknown resonance structures to the cross section for the production of $\eta $-meson $\rho(R_{\to2\gamma}/\eta_{\to2\gamma}) < 3.2 \times 10^{-3}$ at the $95\%$ confidence level.