Internal particle width effects on the triangle singularity mechanism in the study of the η(1405) and η(1475) puzzle

In this article, the analyticity of triangle loop integral with complex masses of internal particles is discussed in a new perspective, based on which we obtain the explicit width dependence of the absorptive part of the triangle amplitude. We reanalyze the decay pattern of $\ensuremath{\eta}(1405/1475)$ with the width effects included in the triangle singularity (TS) mechanism. Based on the present experimental information, we provide a self-consistent description of the $K\overline{K}\ensuremath{\pi}$, $\ensuremath{\eta}\ensuremath{\pi}\ensuremath{\pi}$, and $3\ensuremath{\pi}$ decay channels for $\ensuremath{\eta}(1405/1475)$. Our results confirm the claim that the TS mechanism plays a decisive role in the understanding of the $\ensuremath{\eta}(1405)$ and $\ensuremath{\eta}(1475)$ puzzle. Namely, the observed differences of $\ensuremath{\eta}$ resonances within the mass region of 1.40--1.48 GeV are originated from the same state. For the isospin violated process $J/\ensuremath{\psi}\ensuremath{\rightarrow}\ensuremath{\gamma}\ensuremath{\eta}(1405/1475)\ensuremath{\rightarrow}{f}_{0}(980)\ensuremath{\pi}\ensuremath{\rightarrow}3\ensuremath{\pi}$, we identify an additional contribution to the ${a}_{0}(980)\ensuremath{-}{f}_{0}(980)$ mixing via the TS mechanism.