First measurement of coherent φ -meson photoproduction from He 4 near threshold
© 2018 American Physical Society. The differential cross sections and decay angular distributions for coherent φ-meson photoproduction from helium-4 are measured for the first time at forward angles with linearly polarized photons in the energy range Eγ=1.685-2.385GeV. Thanks to the target with spin-parity JP=0+, 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 (>94%) of natural-parity exchanges in this reaction. To evaluate the contribution from natural-parity exchanges to the forward cross section (θ=0â) for the γp→φp reaction near threshold, the energy dependence of the forward cross section (θ=0â) for the γHe4→φHe4 reaction is analyzed. The comparison to γp→φp 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 γp→φp reaction near threshold.
Hiraiwa, T.; Yosoi, M.; Niiyama, M.; Morino, Y.; Nakatsugawa, Y.; Sumihama, M.; Ahn, D. S.; Ahn, J. K.; Chang, W. C.; Chen, J. Y.; Daté, S.; Fujimura, H.; Fukui, S.; Hicks, K.; Hotta, T.; Hwang, S. H.; Ishikawa, T.; Kato, Y.; Kawai, H.; Kohri, H.; Kon, Y.; Lin, P. J.; Maeda, Y.; Miyabe, M.; Mizutani, K.; Muramatsu, N.; Nakano, T.; Nozawa, Y.; Ohashi, Y.; Ohta, T.; Oka, M.; and Rangacharyulu, C., "First measurement of coherent φ -meson photoproduction from He 4 near threshold" (2018). Physics & Astronomy Open Access Publications. 114.