Abstract
A chiral quark-model approach is adopted to study the $\gamma p\rightarrow \eta'p$ and $\gamma n\rightarrow \eta' n$. Good descriptions of the recent observations from CLAS and CBELSA/TAPS are obtained. Both of the processes are governed by $S_{11}(1535)$ and $u$ channel background. Strong evidence of an $n=3$ shell resonance $D_{15}(2080)$ is found in the reactions, which accounts for the bump-like structure around $W=2.1$ GeV observed in the total cross section and excitation functions at very forward angles. The $S_{11}(1920)$ seems to be needed in the reactions, with which the total cross section near threshold for the $\gamma p\rightarrow \eta' p$ is improved slightly. The polarized beam asymmetries show some sensitivities to $D_{13}(1520)$, although its effects on the differential cross sections and total cross sections are negligible. There is no obvious evidence of the $P$-, $D_{13}$-, $F$- and $G$-wave resonances with a mass around 2.0 GeV in the reactions.
Highlights
The threshold energy of the γp → η′ p and γn → η′n reactions is above the second resonance region, which might be a good place to extract information of the less-explored higher nucleon resonances around 2.0 GeV
They found the dominance of S wave in the η′ production, and the off-shell S 11(1535) excitation played an important role near the η′ threshold
To clarify the structures from the above analyses and observations, we present a systemic analysis of the recent experimental data for γp → pη′ and γn → η′n in the framework of a chiral quark model as an improvement of the previous studies [5, 6]
Summary
The threshold energy of the γp → η′ p and γn → η′n reactions is above the second resonance region, which might be a good place to extract information of the less-explored higher nucleon resonances around 2.0 GeV. Zhang et al [4] first analyzed the old data with an effective Lagrangian approach, in which the off-shell contributions from the low-lying resonances in (1.5 ∼ 1.7) GeV were excluded. Li [5] and Zhao [6] studied the reaction within a constituent quark model approach They found the dominance of S wave in the η′ production, and the off-shell S 11(1535) excitation played an important role near the η′ threshold. In the quark model Li [5] and Zhao [6] found a bump structure around W = 2.1 GeV (Eγ ≃ 2.0 GeV) in the cross section by analyzing the old data. The later higher-precision free proton data from the CLAS Collaboration [11, 12] show a broad bump structure in the cross section around W = 2.1 GeV.
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