Abstract
The differential cross sections and decay angular distributions for coherent -meson photoproduction from helium-4 are measured for the first time at forward angles with linearly polarized photons in the energy range . Thanks to the target with spin-parity , unnatural-parity exchanges are absent, and thus natural-parity exchanges can be investigated clearly. The decay asymmetry with respect to photon polarization is shown to be very close to the maximal value. This ensures the strong dominance (%) of natural-parity exchanges in this reaction. To evaluate the contribution from natural-parity exchanges to the forward cross section () for the reaction near threshold, the energy dependence of the forward cross section () for the reaction is analyzed. The comparison to data suggests that enhancement of the forward cross section arising from natural-parity exchanges and/or destructive interference between natural-parity and unnatural-parity exchanges is needed in the reaction near threshold.
- Received 3 November 2017
- Revised 21 January 2018
DOI:https://doi.org/10.1103/PhysRevC.97.035208
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