Polarization of prompt $J/\psi$ and ${\rm Y}$(1S) production in the color evaporation model

Abstract

We calculate the polarization of prompt $J/\psi$ and ${\rm Y}$(1S) production using the color evaporation model at leading order. We present the polarization parameter ${\lambda }_{\vartheta }$ as a function of center of mass energy and rapidity in $p+p$ collisions. We also compare the $x_F$ dependence to experimental results in $p$+Cu and $\pi$+W collisions, and predict the $x_F$ dependence in $p$+Pb collisions at fixed-target energies. At energies far above the $Q\overline{Q}$ production threshold, we find the prompt $J/\psi$ and ${\rm Y}$(1S) production to be longitudinally polarized with ${\lambda }_{\vartheta }^{J/\psi }=-0.51_{-0.16}^{+0.05}$ and ${\lambda }_{\vartheta }^{{\rm Y}(1S)}=-0.69_{-0.02}^{+0.03}$. Both prompt $J/\psi$ and prompt ${\rm Y}$(1S) are also longitudinally polarized at central rapidity, becoming transversely polarized at the most forward rapidities.

Comments: arXiv admin note: substantial text overlap with arXiv:1702.07809