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.