Study of the resonance structures in $e^{+}e^{-} \rightarrow \pi^{+}\pi^{-}J/\psi$ process

TL;DR

This study precisely measures the cross section of the process $e^{+}e^{-} ightarrow \pi^{+}\pi^{-}J/\psi$ across a range of energies, identifying two resonant structures and suggesting a possible third resonance near 4.5 GeV.

Contribution

First precise measurement of the energy-dependent cross section revealing two new resonance structures, with potential evidence for a third resonance, advancing understanding of charmonium-like states.

Findings

Observation of $Y(4220)$ and $Y(4320)$ with high significance

Determination of their masses and widths

Possible additional resonance near 4.5 GeV

Abstract

Using about 23 $\mathrm{fb^{-1}}$ of data collected with the BESIII detector operating at the BEPCII storage ring, a precise measurement of the $e^{+}e^{-} \rightarrow \pi^{+}\pi^{-}J/\psi$ Born cross section is performed at center-of-mass energies from 3.7730 to 4.7008 GeV. Two structures, identified as the $Y(4220)$ and the $Y(4320)$ states, are observed in the energy-dependent cross section with a significance larger than $10\sigma$. The masses and widths of the two structures are determined to be ($M, \Gamma$) = ($4221.4\pm1.5\pm2.0$ MeV/$c^{2}$, $41.8\pm2.9\pm2.7$ MeV) and ($M, \Gamma$) = ($4298\pm12\pm26$ MeV/$c^{2}$, $127\pm17\pm10$ MeV), respectively. A small enhancement around 4.5 GeV with a significance about $3\sigma$, compatible with the $\psi(4415)$, might also indicate the presence of an additional resonance in the spectrum. The inclusion of this additional contribution in the fit to the cross section affects the resonance parameters of the $Y(4320)$ state.