Low-energy eta-nucleon interaction studied with eta photoproduction off the deuteron
Low-energy eta-nucleon interaction studied with eta photoproduction off the deuteron
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利用氘核的 eta 光产生研究低能 eta-核子相互作用
DOI：
10.1103/physrevc.96.042201
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发表时间：
2017
影响因子：
3.1
通讯作者：
T. Univ.
中科院分区：
文献类型：
--
作者：
S. Nakamura;H. Kamano;T. Univ.;Universidade Cruzeiro do Sul;Kek;J;Elph;T. Univ.
我们发展了一个反应模型$\eta$光生产的氘核（$\gamma d\to\eta pn$），并在一个特殊的运动学下研究反应，其中光子束能量为$\sim 0. 94 $ GeV，散射质子在$\sim 0 ^\circ $处被探测到，为了确定$\eta$-核子散射长度（$a_{\eta N}$）和有效射程（$r_{\eta N}$）。在这种运动学中，$\eta$-核子弹性再散射显着增强，而其他背景机制被抑制。我们表明，比率R，即$\gamma d\to\eta pn$截面除以$\gamma p\to\eta p $截面与氘中质子动量分布的卷积，具有很好的分辨能力a_{\eta N}$和r_{\eta N}$。我们的结论是，$R$数据与5%的误差，在1 MeV的宽度的$\eta$-中子不变质量，可以确定${\rm Re}[a_{\eta N}]$（${\rm Re}[r_{\eta N}]$）在$\sim\pm$0.1 fm（$\sim\pm$0.5 fm）的精度，显着缩小了以前估计的参数范围。为了得出结论，它是必不可少的使用$\gamma d\to\eta pn$反应模型配备了基本的振幅，以及通过复杂的耦合通道分析的$\pi N$和$\gamma N$反应数据的约束。这一结果极大地推动了东北大学电子光子科学研究中心（ELPH）测量R$。
We develop a reaction model for $\eta$ photoproduction off the deuteron ($\gamma d\to\eta pn$), and study the reaction at a special kinematics, where the photon beam energy is $\sim 0.94$ GeV and the scattered proton is detected at $\sim 0^\circ$, for the purpose of determining the $\eta$-nucleon scattering length ($a_{\eta N}$) and effective range ($r_{\eta N}$). In this kinematics, the $\eta$-nucleon elastic rescattering is significantly enhanced while other background mechanisms being suppressed. We show that a ratio $R$, the $\gamma d\to\eta pn$ cross section divided by the $\gamma p\to\eta p$ cross section convoluted with the proton momentum distribution in the deuteron, has a very good resolving power of $a_{\eta N}$ and $r_{\eta N}$. We conclude that the $R$ data with 5% error, binned in 1 MeV width of the $\eta$-neutron invariant mass, can determine ${\rm Re}[a_{\eta N}]$ (${\rm Re}[r_{\eta N}]$) at the precision of $\sim\pm$0.1 fm ($\sim\pm$0.5 fm), significantly narrowing down the previously estimated ranges of the parameters. To arrive at the conclusion, it is essential to use the $\gamma d\to\eta pn$ reaction model equipped with elementary amplitudes that are well constrained by $\pi N$ and $\gamma N$ reaction data through a sophisticated coupled-channels analysis. This result strongly motivates the Research Center for Electron Photon Science (ELPH) at Tohoku University to measure $R$.