On the widths of $\eta (1295)$ and $\eta (1405/1475)$

Abstract

Based on the assignment of the first radial excitation states of the isoscalar pseudoscalars for $\eta (1295)$ and $\eta (1405/1475)$, we investigate their three-body and four-body decay contributions to the total widths. In agreement with our previous studies we find that the triangle singularity (TS) mechanism arising from the intermediate $K^{\ast }\bar{K}$ rescatterings by exchanging a kaon or pion plays a crucial role in both $K\bar{K}\pi$ and $\eta \pi \pi$ channels. For the ${\eta }_X$ (${\eta }_X$ stands for $\eta (1295)$ and $\eta (1405/1475)$) decays into $K\bar{K}\pi$, we find that although the transition ${\eta }_X\to K^{\ast }\bar{K}+c.c.\to K\bar{K}\pi$ is the dominant tree-level process, the productions of the intermediate $K\bar{\kappa }+c.c.$ and $a_0(980)\pi$ are strongly enhanced by the TS mechanism. For the ${\eta }_X$ decays into $\eta \pi \pi$, we find that the production of the intermediate $a_0(980)\pi$ via the triangle transition is the dominant one for $\eta (1295)$ partly because of the large $\eta (1295)K^{\ast }\bar{K}$ coupling. In contrast, the tree-level and triangle loop contributions are compatible and dominant in the $\eta (1405/1475)$ decays into $\eta \pi \pi$. It shows that a combined analysis is useful for disentangling the underlying dynamics for these two states.

Comments: 17 pages and 7 figures