论文标题
低能的分散分析$γn\toπn$过程和$ n^*（890）$共振的研究
Dispersive Analysis of Low Energy $γN\toπN$ Process and Studies on the $N^*(890)$ Resonance
论文作者
论文摘要
我们提出了基于单位性和分析性的$γn\rightarrowπn$部分波幅度的分散表示。在此表示中，右手切割的贡献负责$πn$最终状态相互作用效果通过Omnés形式主义考虑，其弹性$πn$相移作为输入，而左手切割的贡献是通过援引手性扰动理论来估算的。进行数值拟合是为了固定涉及的减法常数。发现只有一个免费参数可以实现良好的拟合质量，并且在$δ（1232）$下方的能量区域中的多极振幅$ e_ {0}^+$的实验数据得到很好的描述。此外，我们将$γn\ rightArrowπn$部分波幅度扩展到第二个riemann板，以提取$ n^\ ast（890）$的耦合。多重振幅$ e_ {0}^+$（$ s_ {11pe} $）的残留物的模量为$ 2.41 \ rm {mfm \ cdot gev^2} $，$ n^*（890）\ to the peo y的$ n^*（; $ n^*（1535）$的$，表明$ n^\ ast（890）$ couples to $πn$ system。
We present a dispersive representation of the $γN\rightarrow πN$ partial-wave amplitude based on unitarity and analyticity. In this representation, the right-hand-cut contribution responsible for $πN$ final-state-interaction effect are taken into account via an Omnés formalism with elastic $πN$ phase shifts as inputs, while the left-hand-cut contribution is estimated by invoking chiral perturbation theory. Numerical fits are performed in order to pin down the involved subtraction constants. It is found that good fit quality can be achieved with only one free parameter and the experimental data of the multipole amplitude $E_{0}^+$ in the energy region below the $Δ(1232)$ are well described. Furthermore, we extend the $γN\rightarrow πN$ partial-wave amplitude to the second Riemann sheet so as to extract the couplings of the $N^\ast(890)$. The modulus of the residue of the multipole amplitude $E_{0}^+$ ($S_{11pE}$) is $2.41\rm{mfm\cdot GeV^2}$ and the partial width of $N^*(890)\toγN$ at the pole is about $0.369\ {\rm MeV}$, which is almost the same as the one of $N^*(1535)$, indicating that $N^\ast(890)$ strongly couples to $πN$ system.
