Meson loop singularity, exotic states' productions and decays near threshold

TL;DR

This paper explores how meson loop triangle singularities near thresholds can enhance certain particle production and decay processes, providing insights into exotic states like Y(4260) and Zc(3900).

Contribution

It demonstrates that meson loop singularities can explain threshold enhancements and relate the production mechanisms of Y(4260) and Zc(3900).

Findings

Meson loop singularities enhance threshold production.

Y(4260) and Zc(3900) are connected via this mechanism.

Threshold enhancements can be explained by near-on-shell meson loops.

Abstract

We investigate in detail the "triangle singularity" regions of meson loops where the corresponding intermediate mesons are nearly-on-shell and have relatively small momenta, and the two heavy mesons strongly interact with each other in an $S$ wave. This $S$-wave interaction will make such kind of meson loops always enhanced and can explain experimental observations of threshold enhancements. We show that the production of the $Y(4260)$ and the recently observed $Z_c(3900)$ can be related to each other by this mechanism which will allow for a possible understanding of the nature of these threshold enhancements.