On a possible origin of a resonance-like structure in the two-photon invariant mass spectrum of the reaction pp->ppgg

Abstract

We show that the resonance-like structure found by the \emph{CELSIUS-WASA Collaboration} in the two-photon invariant mass spectrum of the reaction $pp \to pp γγ$ is rather a signature of the $NN$-decoupled dibaryon resonance $d^\star_1$(1956) that is produced in the radiative process $pp \to γd^\star_1$ and then undergoes radiative decay into two protons $d^\star_1 \to pp γ$. It is found that a contribution of the dibaryon mechanism $pp \to γd^\star_1 \to pp γγ$ of the reaction $pp \to pp γγ$ to the invariant mass spectrum of its photon pairs can reasonably well reproduce the experimentally observed spectrum in the vicinity of the resonance-like structure.