Beam asymmetry $\Sigma$ for the photoproduction of $\eta$ and $\eta'$ mesons at $E_\gamma$=8.8 GeV

Abstract

We report on the measurement of the beam asymmetry $\Sigma$ for the reactions $\vec{\gamma}p$ $\rightarrow$ $p\eta$ and $\vec{\gamma}p$ $\rightarrow$ $p\eta'$ from the GlueX experiment using an 8.2–8.8-GeV linearly polarized tagged photon beam incident on a liquid hydrogen target in Hall D at Jefferson Laboratory. These measurements are made as a function of momentum transfer $-t$ with significantly higher statistical precision than our earlier $\eta$ measurements and are the first measurements of $\eta'$ in this energy range. We compare the results to theoretical predictions based on $t$-channel quasiparticle exchange. We also compare the ratio of $\Sigma_{\eta}$ to $\Sigma_{\eta'}$ to these models as this ratio is predicted to be sensitive to the amount of $s\overline{s}$ exchange in the production. We find that photoproduction of both $\eta$ and $\eta'$ is dominated by natural parity exchange with little dependence on $-t$.