Eta Photoproduction on the proton revisited: Evidence for a narrow N(1685) resonance

Abstract

Revised analysis of $\hat{I}\pounds$ beam asymmetry for $\hat{I}\cdot$ photoproduction on the free proton reveals a resonant structure at $W\sim 1.69$ GeV. Comparison of experimental data with multipole decomposition based on the E429 solution of the SAID partial wave analysis and including narrow states, suggests a narrow ($\hat{I}“\le 15$ MeV) resonance. Possible candidates are $P_{11}$, $P_{13}$, or $D_{13}$ resonances. The result is considered in conjunction with the recent evidence for a bump-like structure at $W\sim 1.67-1.68$ GeV in quasi-free $\hat{I}\cdot$ photoproduction on the neutron.

5 pages, 4 figures