Search for eta' Bound Nuclei in the C-12(gamma,p) Reaction with Simultaneous Detection of Decay Products

Abstract

We measured missing mass spectrum of the C-12(gamma, p) reaction for the first time in coincidence with potential decay products from q' bound nuclei. We tagged an (eta + p) pair associated with the eta'N -> eta N process in a nucleus. After applying kinematical selections to reduce backgrounds, no signal events were observed in the bound-state region. An upper limit of the signal cross section in the opening angle theta(eta 9)(lab) < -0.9 was obtained to be 2.2 nb/sr at the 90% confidence level. It is compared with theoretical cross sections, whose normalization ambiguity is suppressed by measuring a quasifree eta' production rate. Our results indicate a small branching fraction of the eta'N -> eta N process and/or a shallow eta'-nucleus potential.