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arXiv 1505.06396nucl-thhep-exhep-phnucl-ex
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手征夸克模型中核子的中性π介子光生

Neutral pion photoproduction on the nucleon in a chiral quark model

Li-Ye Xiao, Xu Cao, Xian-Hui Zhong

备注：
20 pages, 17 figures
发表信息：
Phys. Rev. C 92, 035202 (2015)
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摘要：

采用手征夸克模型方法研究了$γp\rightarrow π^0p$和$γn\rightarrow π^0 n$反应。从π介子的产生阈值到第二共振区，得到了对总截面、微分截面和单极化观测量的良好描述。发现（i）$n=0$壳层共振$Δ(1232)P_{33}$、$n=1$壳层共振$N(1535)S_{11}$和$N(1520)D_{13}$以及$n=2$壳层共振$N(1720)P_{13}$在这两个过程中起着关键作用。它们分别负责横截面中的第一、第二和第三凸块结构。(ii)此外，在反应中还发现了明显的$N(1650)S_{11}$和$Δ(1620)S_{31}$的证据。它们显著地影响从第二共振区到第三共振区的截面和偏振观测量。(iii)$u$通道背景在反应中起着至关重要的作用。它对$s$通道共振有很强的干扰。(iv)在反应中似乎需要$t$通道背景。在考虑$t$通道矢量介子交换贡献的情况下，$E_γ= 600\sim 900$ MeV能区的描述得到了显著的改进.提取了主共振$Δ(1232)P_{33}$、$N(1535)S_{11}$、$N(1520)D_{13}$、$N(1720)P_{13}$、$N(1650)S_{11}$和$Δ(1620)S_{31}$的螺旋度振幅，并与其他组的结果进行了比较。

英文摘要：

A chiral quark-model approach is adopted to study the $γp\rightarrow π^0p$ and $γn\rightarrow π^0 n$ reactions. Good descriptions of the total and differential cross sections and single-polarization observables are obtained from the pion production threshold up to the second resonance region. It is found that (i) the $n=0$ shell resonance $Δ(1232)P_{33}$, the $n=1$ shell resonances $N(1535)S_{11}$ and $N(1520)D_{13}$, and the $n=2$ shell resonance $N(1720)P_{13}$ play crucial roles in these two processes. They are responsible for the first, second and third bump structures in the cross sections, respectively. (ii) Furthermore, obvious evidences of $N(1650)S_{11}$ and $Δ(1620)S_{31}$ are also found in the reactions. They notably affect the cross sections and the polarization observables from the second resonance region to the third resonance region. (iii) The $u$-channel background plays a crucial role in the reactions. It has strong interferences with the $s$-channel resonances. (iv) The $t$-channel background seems to be needed in the reactions. Including the $t$-channel vector-meson exchange contribution, the descriptions in the energy region $E_γ= 600\sim 900$ MeV are improved significantly. The helicity amplitudes of the main resonances, $Δ(1232)P_{33}$, $N(1535)S_{11}$, $N(1520)D_{13}$, $N(1720)P_{13}$, $N(1650)S_{11}$ and $Δ(1620)S_{31}$, are extracted and compared with the results from other groups.

机构、总结、中文摘要均由AI分析而来，可能存在错误，请以论文正文为准。

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