Partial Wave Analysis of $e^{+}e^{-} \rightarrow \pi^{+}\pi^{-}J/\psi$ and Cross Section Measurement of $e^{+}e^{-} \rightarrow \pi^{\pm}Z_{c}(3900)^{\mp}$ from 4.1271 to 4.3583 GeV

TL;DR

This paper performs a detailed partial wave analysis of $e^{+}e^{-} ightarrow \pi^{+}\pi^{-} ext{ extbackslash} J/ ext{ extbackslash}psi$ using BESIII data, measuring cross sections and properties of intermediate states, and observing the $Y(4220)$ resonance.

Contribution

It provides the first measurements of cross sections for specific subprocesses and determines the properties of the $Z_{c}(3900)$ and $Y(4220)$ states from experimental data.

Findings

Mass and width of $Z_{c}(3900)^{ ext{ extbackslash}pm}$ measured.

First measurement of cross sections for subprocesses involving $Z_{c}(3900)$ and $f_{0}(980)$.

Observation of the $Y(4220)$ resonance with determined mass and width.

Abstract

Based on 12.0 $\mathrm{fb^{-1}}$ of $e^{+}e^{-}$ collision data samples collected by the BESIII detector at center-of-mass energies from 4.1271 to 4.3583 GeV, a partial wave analysis is performed for the process $e^{+}e^{-} \rightarrow \pi^{+}\pi^{-}J/\psi$. The cross sections for the sub processes ${e^{+}e^{-}\rightarrow\pi^{+}Z_{c}(3900)^{-}+c.c.\rightarrow\pi^{+}\pi^{-}J/\psi}$, $f_{0}(980)(\rightarrow\pi^{+}\pi^{-})J/\psi$, and $(\pi^{+}\pi^{-})_{\rm{S\mbox{-}wave}} J/\psi$ are measured for the first time. The mass and width of the $Z_{c}(3900)^{\pm}$ are determined to be $3884.6\pm0.7\pm3.3$ MeV/$c^{2}$ and $37.2\pm1.3\pm6.6$ MeV, respectively. The first errors are statistical and the second systematic. The final state $(\pi^{+}\pi^{-})_{\rm{S\mbox{-}wave}} J/\psi$ dominates the process $e^{+}e^{-} \rightarrow \pi^{+}\pi^{-}J/\psi$. By analyzing the cross sections of $\pi^{\pm}Z_{c}(3900)^{\mp}$ and $f_{0}(980)J/\psi$, $Y(4220)$ has been observed. Its mass and width are determined to be $4225.7\pm4.1\pm3.4$ MeV/$c^{2}$ and $57.5\pm9.4\pm12.1$ MeV, respectively.