We report the first measurement of the full angular distribution for inclusive $J/\psi \to {\mu }^{+}{\mu }^{-}$ decays in $p+p$ collisions at $\sqrt{s}=510\mathrm{GeV}$. The measurements are made for $J/\psi$ transverse momentum $2<p_T<10\mathrm{GeV}/c$ 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 ${\lambda }_{\varphi }$ 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.

• Received 21 December 2016

DOI:https://doi.org/10.1103/PhysRevD.95.092003