Measurement of the $e^+e^-\to\pi^+\pi^-J/\psi$ cross section in the vicinity of 3.872 GeV

TL;DR

This study measures the $e^+e^- o ext{pi}^+ ext{pi}^-J/ ext{psi}$ cross section near 3.872 GeV to search for direct $X(3872)$ formation, setting new upper limits on its electronic width and branching fraction.

Contribution

The paper provides the first precise upper limits on the electronic width and production cross section of $X(3872)$ in $e^+e^-$ collisions, improving previous constraints significantly.

Findings

No enhancement observed at $X(3872)$ mass

Upper limit on $ ext{Gamma}_{ee} imes ext{B}(X(3872) o ext{pi}^+ ext{pi}^-J/ ext{psi})$

Upper limit on $ ext{Gamma}_{ee}$ of $X(3872)$ is 0.32 eV

Abstract

We report a measurement of the cross section for the process $e^+e^-\to\pi^+\pi^-J/\psi$ around the $X(3872)$ mass in search for the direct formation of $e^+e^-\to X(3872)$ through the two-photon fusion process. No enhancement of the cross section is observed at the $X(3872)$ peak and an upper limit on the product of electronic width and branching fraction of $X(3872)\to\pi^+\pi^-J/\psi$ is determined to be $\Gamma_{ee}\times\mathcal{B}(X(3872)\to\pi^+\pi^-J/\psi)<7.5\times10^{-3}\,\text{eV}$ at $90\,\%$ confidence level under an assumption of total width of $1.19\pm0.21$ MeV. This is an improvement of a factor of about $17$ compared to the previous limit. Furthermore, using the latest result of $\mathcal{B}(X(3872)\to\pi^+\pi^-J/\psi)$, an upper limit on the electronic width $\Gamma_{ee}$ of $X(3872)$ is obtained to be $<0.32\,\text{eV}$ at the $90\,\%$ confidence level.