Observation of sizeable $\omega$ contribution to $\chi_{c1}(3872)\to\pi^+\pi^-J/\psi$ decays

TL;DR

This paper reports the first observation of a significant $ ho^0 J/$ decay contribution in $_{3872}$ decays, indicating notable isospin violation and providing new insights into its structure.

Contribution

It provides the first measurement of the sizeable $_{3872} o\u03a9 J/$ decay contribution and quantifies the isospin violation in $_{3872}$ decays.

Findings

A 21.4% contribution from $_{3872} o\u03a9 J/$ decay.

The isospin violating decay amplitude is six times larger than expected for pure charmonium.

Significance of the $_{3872} o\u03a9 J/$ contribution exceeds 7.1 sigma.

Abstract

Resonant structures in the dipion mass spectrum from $\chi_{c1}(3872)\to\pi^+\pi^- J/\psi$ decays, produced via $B^+\to K^+\chi_{c1}(3872)$ decays, are analyzed using proton-proton collision data collected by the LHCb experiment, corresponding to an integrated luminosity of 9 $fb^{-1}$. A sizeable contribution from the isospin conserving $\chi_{c1}(3872)\to\omega J/\psi$ decay is established for the first time, $(21.4\pm2.3\pm2.0)\%$, with a significance of more than $7.1\sigma$. The amplitude of isospin violating decay, $\chi_{c1}(3872)\to\rho^0 J/\psi$, relative to isospin conserving decay, $\chi_{c1}(3872)\to\omega J/\psi$, is properly determined, and it is a factor of six larger than expected for a pure charmonium state.