Measurements of $e^+e^-\rightarrow \eta_{\rm c}\pi^+ \pi^-\pi^0$, $\eta_{\rm c}\pi^+ \pi^-$ and $\eta_{\rm c}\pi^0\gamma$ at $\sqrt{s}$ from 4.18 to 4.60\,GeV, and search for a $Z_{\rm c}$ state close to the $D\bar{D}$ threshold decaying to $\eta_{\rm c}\pi$ at $\sqrt{s}$ = 4.23 GeV

TL;DR

This study measures $ m extit{eta}_c$ production cross sections in electron-positron collisions at energies from 4.18 to 4.60 GeV, confirming production via the $Y(4260)$ resonance and searching for, but not finding, a $Z_c$ state near the $Dar{D}$ threshold.

Contribution

First measurement of $ m extit{eta}_c$ production cross sections in this energy range and search for a $Z_c$ state decaying to $ m extit{eta}_c extpi$ near the $Dar{D}$ threshold.

Findings

Significant $ m extit{eta}_c$ production at 4.23 and 4.26 GeV

Production consistent with $Y(4260)$ resonance

No evidence for $Z_c$ state near $Dar{D}$ threshold

Abstract

We study $\eta_{\rm c}$ production at center-of-mass energies $\sqrt{s}$ from 4.18 to 4.60 GeV in $e^+e^-$ annihilation data collected with the BESIII detector operating at the BEPCII storage ring, corresponding to 7.3 fb$^{-1}$ of integrated luminosity. We measure the cross sections of the three different exclusive reactions $e^+e^-\rightarrow \eta_{\rm c}\pi^+ \pi^-\pi^0$, $e^+e^- \rightarrow \eta_{\rm c}\pi^+ \pi^-$, and $e^+e^- \rightarrow \eta_{\rm c}\pi^0\gamma$. We find significant $\eta_{\rm c}$ production in $e^+e^-\rightarrow \eta_{\rm c}\pi^+ \pi^-\pi^0$ at $\sqrt{s}$ of 4.23 GeV and 4.26 GeV and observe a significant energy-dependent Born cross section that we measure to be consistent with the production via the intermediate $Y(4260)$ resonance. In addition, we perform a search for a charmonium-like $Z_{\rm c}$ state close to the $D\bar{D}$ threshold that decays to $\eta_{\rm c}\pi$, involving ground state charmonium, and observe no signal. Corresponding upper limits on the cross section of $\eta_{\rm c}$ and $Z_{\rm c}$ production are provided, where the yields are not found to be significant.