Threshold effects as the origin of $Z_{cs}(4000)$, $Z_{cs}(4220)$ and $X(4700)$ observed in $B^+\to J/\psi \phi K^+$

TL;DR

This paper explains certain exotic states observed in B+ decays as threshold cusps enhanced by triangle singularities, without requiring genuine exotic resonances, but suggests some states may be true resonances.

Contribution

It demonstrates that specific exotic states can be explained by threshold effects and triangle singularities, challenging the need for genuine resonances in these cases.

Findings

$Z_{cs}(4000)$, $Z_{cs}(4220)$, and $X(4700)$ can be explained as threshold cusps.

Threshold cusps are enhanced by nearby triangle singularities.

The $X(4685)$ likely represents a genuine resonance.

Abstract

We investigate the $B^+\to J/\psi \phi K^+$ decay via various rescattering diagrams. Without introducing genuine exotic resonances, it is shown that the $Z_{cs}(4000)$, $Z_{cs}(4220)$ and $X(4700)$ reported by the LHCb collaboration can be simulated by the $J/\psi K^{*+}$, $\psi^\prime K^+$ and $\psi^\prime \phi$ threshold cusps, respectively. These cusps are enhanced by some nearby triangle singularities. The $X(4685)$ with $J^P=1^+$ cannot be well simulated by the threshold effects in our model, which implies that it may be a genuine resonance.