Interference effect as resonance killer of newly observed charmoniumlike states $Y(4320)$ and $Y(4390)$

TL;DR

This paper explains the observed charmoniumlike states $Y(4320)$ and $Y(4390)$ as interference effects rather than genuine resonances, introducing a new structure $Y(4220)$ and emphasizing non-resonant explanations for $XYZ$ states.

Contribution

It introduces an interference-based explanation for $Y(4320)$ and $Y(4390)$, challenging their interpretation as genuine resonances and proposing $Y(4220)$ as a real state.

Findings

$Y(4320)$ and $Y(4390)$ are not genuine resonances but interference effects.

A new structure $Y(4220)$ is necessary to fit the data.

$Y(4220)$ likely decays into open-charm channels, supporting its assignment as $ ext{psi}(4S)$.

Abstract

In this letter, we decode the newly observed charmoniumlike states, $Y(4320)$ and $Y(4390)$, by introducing interference effect between $\psi(4160)$ and $\psi(4415)$, which plays a role of resonance killer for $Y(4320)$ and $Y(4390)$. It means that two newly reported charmoniumlike states are not genuine resonances, according to which we can naturally explain why two well-established charmonia $\psi(4160)$ and $\psi(4415)$ are missing in the cross sections of $e^+e^- \to \pi^+ \pi^- J/\psi$ and $\pi^+ \pi^- h_c$ simultaneously. To well describe the detailed data of these cross sections around $\sqrt{s}=4.2$ GeV, our study further illustrates that a charmoniumlike structure $Y(4220)$ must be introduced. As a charmonium, $Y(4220)$ should dominantly decay into its open-charm channel $e^+e^- \to D^0 \pi^+ D^{\ast-}$, which provides an extra support to $\psi(4S)$ assignment to $Y(4220)$. In fact, this interference effect introduced to explain $Y(4320)$ and $Y(4390)$ gives a typical example of non-resonant explanations to the observed $XYZ$ states, which should be paid more attention especially before identifying the observed $XYZ$ states as genuine resonances.