Measurement of inclusive J/$\ddot{I}ˆ$ polarization in p+p collisions at $\sqrt{s}$ = 200 GeV by the STAR experiment

Abstract

We report on new measurements of inclusive J/$\ddot{I}ˆ$ polarization at mid-rapidity in p+p collisions at $\sqrt{s}$ = 200 GeV by the STAR experiment at RHIC. The polarization parameters, $\hat{I}{»}_{\hat{I}}¸$, $\hat{I}{»}_{\ddot{I}}•$, and $\hat{I}{»}_{\hat{I}¸\ddot{I}•}$, are measured as a function of transverse momentum ($p_T$) in both the Helicity and Collins-Soper (CS) reference frames within $p_T<10$ GeV/$C$. Except for $\hat{I}{»}_{\hat{I}}¸$ in the CS frame at the highest measured $p_T$, all three polarization parameters are consistent with 0 in both reference frames without any strong $p_T$ dependence. Several model calculations are compared with data, and the one using the Color Glass Condensate effective field theory coupled with non-relativistic QCD gives the best overall description of the experimental results, even though other models cannot be ruled out due to experimental uncertainties.

14 pages, 11 figures