Abstract
Differential cross sections and photon-beam asymmetries for the reaction have been measured for and at SPring-8/LEPS. The first-ever high statistics cross-section data are obtained in this kinematical region, and the asymmetry data for are obtained for the first time. This reaction has a unique feature for studying the production mechanisms of a pure quark pair in the final state from the proton. Although there is no distinct peak structure in the cross sections, a non-negligible excess over the theoretical predictions is observed at . The asymmetries are found to be negative in most of the present kinematical regions, suggesting the dominance of exchange in the channel. The negative asymmetries at forward meson production angles are different from the asymmetries previously measured for the photoproduction reactions producing a or an quark pair in the final state. Advanced theoretical models introducing nucleon resonances and additional unnatural-parity exchanges are needed to reproduce the present data.
- Received 24 January 2018
- Revised 11 March 2018
DOI:https://doi.org/10.1103/PhysRevLett.120.202004
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