Observation of a charged charmoniumlike structure in $e^+e^- \to (D^{*} \bar{D}^{*})^{\pm} \pi^\mp$ at $\sqrt{s}=4.26$GeV

TL;DR

This paper reports the observation of a charged charmoniumlike structure, Z_c(4025), near the D* D* threshold in e+e- collisions at 4.26 GeV, with measurements of its properties and production ratio, indicating a possible exotic state.

Contribution

First observation of the Z_c(4025) structure in e+e- to D* D* pi at 4.26 GeV, providing detailed measurements of its mass, width, and production ratio.

Findings

Observed a structure near the D* D* threshold, named Z_c(4025).

Measured the mass as approximately 4026 MeV/c^2 and width as about 25 MeV.

Determined the production ratio of Z_c(4025) in the process.

Abstract

We study the process $e^+e^- \to (D^{*} \bar{D}^{*})^{\pm} \pi^\mp$ at a center-of-mass energy of 4.26GeV using a 827pb$^{-1}$ data sample obtained with the BESIII detector at the Beijing Electron Positron Collider. Based on a partial reconstruction technique, the Born cross section is measured to be $(137\pm9\pm15)$pb. We observe a structure near the $(D^{*} \bar{D}^{*})^{\pm}$ threshold in the $\pi^\mp$ recoil mass spectrum, which we denote as the $Z^{\pm}_c(4025)$. The measured mass and width of the structure are $(4026.3\pm2.6\pm3.7)$MeV/c$^2$ and $(24.8\pm5.6\pm7.7)$MeV, respectively. Its production ratio $\frac{\sigma(e^+e^-\to Z^{\pm}_c(4025)\pi^\mp \to (D^{*} \bar{D}^{*})^{\pm} \pi^\mp)}{\sigma(e^+e^-\to (D^{*} \bar{D}^{*})^{\pm} \pi^\mp)}$ is determined to be $0.65\pm0.09\pm0.06$. The first uncertainties are statistical and the second are systematic.