N. Tomida, T.N.T.Ngan, et al.
Physical Review Letters 124, 202501 (2020)
Abstract:
We measured missing mass spectrum of the 12C(γ,p) reaction for the first time in coincidence with potential decay products from η' bound nuclei. We tagged an (η + p) pair associated with the η'N → ηN process in a nucleus. After applying kinematical selections to reduce backgrounds, no signal events were observedinthebound-stateregion.An upper limit of the signal cross section in the opening angle cosθηplab < -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 η' production rate. Our results indicate a small branching fraction of the η'N → ηN process and/or a shallow η'-nucleus potential.
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