Evidence for $X(3872)\rightarrow J/\psi \pi^+\pi^-$ produced in single-tag two-photon interactions

TL;DR

This study provides the first evidence of the $X(3872)$ particle produced via two-photon interactions in high-energy electron-positron collisions, using tagged virtual photons, and measures its production rate relative to theoretical models.

Contribution

It reports the first observation of $X(3872)$ in two-photon interactions with virtual photons, expanding understanding of its production mechanisms and testing meson models.

Findings

Observed 3 $X(3872)$ candidates with 3.2$\sigma$ significance.

Estimated the two-photon decay width times branching ratio for $X(3872)$.

No evidence found for $X(3915)$ in the studied decay channel.

Abstract

We report the first evidence for $X(3872)$ production in two-photon interactions by tagging either the electron or the position in the final state, exploring the highly virtual photon region. The search is performed in $e^+e^- \rightarrow e^+e^-J/\psi\pi^+\pi^-$, using 825 fb$^{-1}$ of data collected by the Belle detector operated at the KEKB $e^+e^-$ collider. We observe three $X(3872)$ candidates with an expected background of $0.11\pm 0.10$ events, with a significance of 3.2$\sigma$. We obtain an estimated value for $\tilde{\Gamma}_{\gamma\gamma}{\cal B}(X(3872)\rightarrow J/\psi\pi^+\pi^-$) assuming the $Q^2$ dependence predicted by a $c\bar{c}$ meson model, where $-Q^2$ is the invariant mass-squared of the virtual photon. No $X(3915)\rightarrow J/\psi\pi^+\pi^-$ candidates are found.