Differential cross sections and photon beam asymmetries of $\eta$ photoproduction on the proton at $E_{\gamma }$ = 1.3-2.4 GeV

Abstract

We have carried out exclusive measurements for the photoproduction of an $\eta$ meson from a proton target with an egg-shaped calorimeter made of BGO crystals (BGOegg) and forward charged-particle detectors at the SPring-8 LEPS2 beamline. The differential cross sections and photon beam asymmetries of the $\gamma p\to \eta p$ reaction are measured in a center-of-mass energy ($W$) range of $1.82$-$2.32$ GeV and a polar angle range of $-1.0<\cos {\theta }_{c.m.}^{\eta }<0.6$. The reaction is identified by selecting a proton and two $\gamma$'s produced by an $\eta$-meson decay. The kinematic fit method was employed to select the reaction candidate with the confidence level larger than $1$\%. A bump structure at $W$ = $2.0$-$2.3$ GeV in the differential cross section is confirmed at extremely backward $\eta$ polar angles, where the existing data are inconsistent with each other. This bump structure is likely associated with high-spin resonances that couple with $s\bar{s}$ quarks. The results of the photon beam asymmetries in a wide $\eta$ polar angle range are new for the photon beam energies exceeding $2.1$ GeV. These results are not reproduced by the existing partial wave analyses. They provide an additional constraint to nucleon resonance studies at high energies.

16 pages, 11 figures

References in corpus (5)

• Measurement of eta photoproduction on the proton from threshold to 1500 MeV
• Eta photoproduction in a combined analysis of pion- and photon-induced reactions
• SPring-8 LEPS2 beamline: A facility to produce a multi-GeV photon beam via laser Compton scattering
• Observation of the $p{\eta }^{\prime }$ Cusp in the New Precise Beam Asymmetry $\Sigma$ Data for $\gamma p\to p\eta$
• Exclusive Meson Photo- and Electro-production, a Window on the Structure of Hadronic Matter

Cited by in corpus (3)

• Direct measurement of the in-medium ${\eta }^{\prime }$ mass spectrum through the $\gamma \gamma$ decay channel
• Comprehensive measurement of ${\eta }^{\prime }$ photoproduction off the proton at $E_{\gamma }<2.4$ $\mathrm{GeV}$
• Coupled-channel contributions to the GDH sum rule from the Jülich-Bonn approach