The LEPS/SPring-8 experiment made a comprehensive measurement of the spin-density matrix elements for γp→p, γd→pn, and γd→d at forward production angles. A linearly polarized photon beam at Eγ=1.6-2.4 GeV was used for the production of mesons. The natural-parity Pomeron exchange processes remain dominant near threshold. The unnatural-parity processes of pseudoscalar exchange is visible in the production from the nucleons but is greatly reduced in the coherent production from deuterons. There is no strong Eγ dependence, but there is some dependence on momentum transfer. A small but finite value of the spin-density matrix elements reflecting helicity-nonconserving amplitudes in the t-channel is observed.
ASJC Scopus subject areas
- Nuclear and High Energy Physics