Angular decay coefficients of $J/\psi$ mesons at forward rapidity from $p+p$ collisions at $\sqrt{s}=510$ GeV

TL;DR

This study measures the angular distribution of $J/$ mesons in proton-proton collisions at 510 GeV, revealing polarization patterns and comparing results with quantum chromodynamics models.

Contribution

First measurement of the full angular distribution of $J/$ decays at this energy and kinematic range, providing new data for testing QCD models.

Findings

Polar coefficient $_{ heta}$ is strongly negative at low $p_T$ and approaches zero at high $p_T$.

Azimuthal coefficient $_{\u03c6}$ is near zero at low $p_T$ and slightly negative at higher $p_T$.

Frame-independent coefficient $$ is strongly negative across all $p_T$.

Abstract

We report the first measurement of the full angular distribution for inclusive $J/\psi\rightarrow\mu^{+}\mu^{-}$ decays in $p$$+$$p$ collisions at $\sqrt{s}=510$ GeV. The measurements are made for $J/\psi$ transverse momentum $2<p_{T}<10$ GeV/$c$ and rapidity $1.2<y<2.2$ in the Helicity, Collins-Soper, and Gottfried-Jackson reference frames. In all frames the polar coefficient $\lambda_{\theta}$ is strongly negative at low $p_{T}$ and becomes close to zero at high $p_{T}$, while the azimuthal coefficient $\lambda_{\phi}$ is close to zero at low $p_{T}$, and becomes slightly negative at higher $p_{T}$. The frame-independent coefficient $\tilde{\lambda}$ is strongly negative at all $p_{T}$ in all frames. The data are compared to the theoretical predictions provided by nonrelativistic quantum chromodynamics models.