Comprehensive measurement of $η^\prime$ photoproduction off the proton at $E_γ< 2.4$ $\mathrm{GeV}$

Abstract

For the spectroscopy of nucleon resonances at the total energies from the $η^\prime$-meson production threshold to $2.32$ $\mathrm{GeV}$, photon beam asymmetries of the reaction $γp \to η^\prime p$ were measured together with total and differential cross sections by analyzing the two decay modes $η^\prime \to γγ$ and $π^0 π^0 η$. New constraints for amplitude decomposition were given by the first-time result of photon beam asymmetries at $E_γ> 1.84$ $\mathrm{GeV}$ and the most precise data of differential cross sections to date at extremely backward $η^\prime$ angles. The possibility of a larger coupling constant of the $η^\prime$-nucleon system to the $N(2250)$ resonance was implied in the partial wave analyses using the present data.

Figures (5)

• Figure 1: Invariant mass distributions of (a) $\gamma \gamma$ and (b) $\pi^0 \pi^0 \eta$ in the samples selected for the $2\gamma$ and $6\gamma$ modes, respectively.
• Figure 2: Differential cross sections $d\sigma/d\Omega$ of the reaction $\gamma p \to \eta^\prime p$ depending on the cosine of the $\eta^\prime$ polar angle in the center-of-mass frame, $\cos \theta_{\eta^\prime}^{c.m.}$. Data points with statistical uncertainties (vertical bars) for the present analysis (BGOegg) and the existing results are plotted by the symbols in the legend. Systematic uncertainties for the present result are indicated by the hatched histograms. Two partial wave analysis fits using the present result are also overlaid as explained in the last part of the text.
• Figure 3: Differential cross sections $d\sigma/d\Omega$ of the reaction $\gamma p \to \eta^\prime p$ as a function of the total energy $W$. Only the present result in Fig. \ref{['fig:dcs']} is rearranged with the same notations.
• Figure 4: Total cross sections $\sigma_{tot}$ of the reaction $\gamma p \to \eta^\prime p$, measured by the present analysis (red closed circles) and the CBELSA/TAPS experiment (black open triangles). The notations are the same as those in Fig. \ref{['fig:dcs']}.
• Figure 5: Photon beam asymmetries $\Sigma$ of the reaction $\gamma p \to \eta^\prime p$, plotted for the present analysis (BGOegg) and the existing results indicated in the legend. The notations are the same as those in Fig. \ref{['fig:dcs']} except for showing systematic uncertainties by half the vertical lengths of boxes around the data points.