Quantum numbers of the $X(3872)$ state and orbital angular momentum in its $\rho^0 J\psi$ decay

TL;DR

This paper uses angular correlations in B+ decays to determine the quantum numbers of the X(3872) meson, confirming it has J^{PC}=1^{++} and predominantly decays via S wave, with minimal D wave contribution.

Contribution

First model-independent measurement of the X(3872) quantum numbers using angular correlations in its decay.

Findings

Confirmed X(3872) has quantum numbers J^{PC}=1^{++}

X(3872) decays mainly through S wave

Set an upper limit of 4% on D wave fraction

Abstract

Angular correlations in $B^+\to X(3872) K^+$ decays, with $X(3872)\to \rho^0 J/\psi$, $\rho^0\to\pi^+\pi^-$ and $J/\psi \to\mu^+\mu^-$, are used to measure orbital angular momentum contributions and to determine the $J^{PC}$ value of the $X(3872)$ meson. The data correspond to an integrated luminosity of 3.0 fb$^{-1}$ of proton-proton collisions collected with the LHCb detector. This determination, for the first time performed without assuming a value for the orbital angular momentum, confirms the quantum numbers to be $J^{PC}=1^{++}$. The $X(3872)$ is found to decay predominantly through S wave and an upper limit of $4\%$ at $95\%$ C.L. is set on the fraction of D wave.