Multi-channel joint analysis of the exotic charmonium-like state $T_{c\bar{c}}(4020)$

TL;DR

This study performs the first multi-channel analysis of the exotic state $T_{c\bar{c}}(4020)$, determining its properties, spin-parity, pole positions, and branching fractions using electron-positron collision data.

Contribution

It introduces a simultaneous partial wave analysis across three decay channels to identify the $T_{c\bar{c}}(4020)$ properties and determine its spin-parity for the first time.

Findings

Spin-parity of $T_{c\bar{c}}(4020)$ is $J^{P}=1^{+}$ with $11.7\sigma$ significance.

Pole positions are extracted on complex Riemann sheets.

Relative branching fractions are measured for different decay modes.

Abstract

This paper reports the first multi-channel joint analysis to identify the properties of the exotic charmonium-like state $T_{c\bar{c}}(4020)$ via the electron-positron annihilation process $e^{+}e^{-}\to\pi^{+}T_{c\bar{c}}(4020)^{-}+c.c$. A partial wave analysis is performed simultaneously in three decay channels $T_{c\bar{c}}(4020)^{-}\to {D}^{*0}D^{*-}$, $\pi^{-}J/\psi$, and $\pi^{-}h_{c}$, based on data samples taken at $\sqrt{s}=4.395$ and $4.416\,\mathrm{GeV}$ with an integrated luminosity of $1598.9\,\mathrm{pb}^{-1}$ collected with the BESIII detector operating on the BEPCII collider. For the first time, the spin-parity of the $T_{c\bar{c}}(4020)^{-}$ is determined to be $J^{P}=1^{+}$ with a significance $11.7\sigma$. Pole positions are extracted on the Riemann sheets with three branch points in the complex energy plane. Furthermore, the relative branching fractions are obtained as $\mathcal{B}[T_{c\bar{c}}(4020)^{-}\to\pi^{-}J/\psi]/\mathcal{B}[T_{c\bar{c}}(4020)^{-}\to{D}^{*0}D^{*-}]=(3.6\pm0.6\pm1.6)\times10^{-3}$ and $\mathcal{B}[T_{c\bar{c}}(4020)^{-}\to\pi^{-}h_{c}]/\mathcal{B}[T_{c\bar{c}}(4020)^{-}\to{D}^{*0}D^{*-}]=(8.9\pm1.3\pm2.3)\times10^{-2}$, where the first uncertainties are statistical, and the second are systematic.