Diphoton and dipion productions at the Nuclotron/NICA

Abstract.

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 $d C \rightarrow \gamma + \gamma +X$ at momentum 2.75GeV/c per nucleon. Estimates of its width and production cross section are $\Gamma = 64 \pm 18$ MeV and $\sigma_{\gamma\gamma} = 98 \pm 24^{+93}_{-67}$ μb, 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 the $\gamma$ $\gamma$ channel in $\sim 10^{11} p+ C$ collisions at the beam momentum 5.5GeV/c . The result obtained in the reaction $d+ C$ is confirmed by the second experiment carried out on the deuteron beam at momentum 3.83GeV/c per nucleon with a copper target: $M = 382 \pm 13$ MeV, $\Gamma = 62 \pm 37$ MeV and $\sigma = 273 \pm 75$ μb. Some results on the observation of the resonance in the invariant-mass spectra of two $\pi^{0}$ mesons are presented: the data obtained in the $d+C\rightarrow \gamma+\gamma + X$ reaction is confirmed by the results for the $d+C\rightarrow \pi^{0} +\pi^{0} + X$ and $p+C\rightarrow \pi^{0} +\pi^{0} + X$ reactions; a preliminary estimate of the ratio $Br(R\rightarrow\gamma\gamma)/Br (R\rightarrow\pi^{0}\pi^{0})$ is $(1.8-3.7)\cdot 10^{-3}$ . Further studies of this resonance is assumed at the Nuclotron/NICA at higher setup acceptance, which will allow to elucidate the nature of this resonance by determination of the differential cross sections at different beam energies in the range 1-6GeV/n and the mechanism of its formation.