Backward-angle photoproduction of eta meson from protons at E_gamma = 1.6 - 2.4 GeV

Differential cross sections for eta photoproduction off protons have been measured at E_gamma = 1.6 - 2.4 GeV in the backward direction. A bump structure has been observed above 2.0 GeV in the total energy. No such bump is observed in cross sections for eta, omega and pi0 photoproductions. It is inferred that this unique structure in eta photoproduction is due to a baryon resonance with a large portion of ss-bar strongly coupled to the etaN channel.

Backward-angle photoproduction of $pi^0$ mesons on the proton at $E_gamma$ = 1.5--2.4 GeV

Differential cross sections and photon beam asymmetries for $pi^0$ photoproduction have been measured at $E_gamma$ = 1.5--2.4 GeV and at the $pi^0$ scattering angles, --1 $<$ cos$Theta_{c.m.} <$ --0.6. The energy-dependent slope of differential cross sections for $u$-channel $pi^0$ production has been determined. An enhancement at backward angles is found above $E_gamma$ = 2.0 GeV. This is inferred to be due to the $u$-channel contribution and/or resonances. Photon beam asymmetries have been obtained for the first time at backward angles. A strong angular dependence has been found at $E_gamma >$ 2.0 GeV, which may be due to the unknown high-mass resonances.