Observation of the $Y(4230)$ and a new structure in $e^+e^- \rightarrow K^+K^-J/\psi$

TL;DR

This paper reports the observation of the $Y(4230)$ resonance and a newly discovered structure, $Y(4500)$, in the $e^+e^- ightarrow K^+K^-J/psi$ process, with detailed measurements of their properties based on BESIII data.

Contribution

First observation of the $Y(4500)$ structure in $e^+e^- ightarrow K^+K^-J/psi$ and precise measurements of the $Y(4230)$ parameters.

Findings

Observation of $Y(4230)$ consistent with previous measurements.

First evidence of the $Y(4500)$ resonance with >8$\sigma$ significance.

Measured masses and widths of both structures.

Abstract

The cross sections of $e^+e^- \rightarrow K^+K^-J/\psi$ at center-of-mass energies from 4.127 to 4.600~GeV are measured based on 15.6 fb$^{-1}$ data collected with the BESIII detector operating at the BEPCII storage ring. Two resonant structures are observed in the line shape of the cross sections. The mass and width of the first structure are measured to be ($4225.3\pm2.3\pm21.5$) MeV and ($72.9\pm6.1\pm30.8$)~MeV, respectively. They are consistent with those of the established $Y(4230)$. The second structure is observed for the first time with a statistical significance greater than 8$\sigma$, denoted as $Y(4500)$. Its mass and width are determined to be ($4484.7\pm13.3\pm24.1$) MeV and ($111.1\pm30.1\pm15.2$) MeV, respectively. The first presented uncertainties are statistical and the second ones are systematic. The product of the electronic partial width with the decay branching fraction $ \Gamma(Y(4230)\to e^+ e^-) \mathcal{B}(Y(4230) \to K^+ K^- J/\psi)$ is reported.