Photoproduction off the nucleon revisited: Evidence for a narrow N(1688) resonance?

Abstract

Revised analysis of $\hat{I}\pounds$ beam asymmetry for the $\hat{I}\cdot$ photoproduction on the free proton reveals a structure at $W\sim 1.69$ GeV. Fit of the experimental data based on the E429 solution of the SAID partial wave analysis suggests a narrow ($\hat{I}“\le 25$ 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 the quasi-free $\hat{I}\cdot$ photoproduction on the neutron.

Contribution to the Workshop on the Physics of the Excited Nucleons NSTAR2007, Bonn, Germany, Sept. 5 - 8 2007. To be published in Eur.Phys.J.A