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Schlagwörter:
STAR
Zusammenfassung:
We report on new measurements of inclusive J/\psi polarization at mid-rapidity in p+p collisions at sqrt{s} = 200 GeV by the STAR experiment at RHIC. The polarization parameters, \lambda_\theta, \lambda_\phi, and \lambda_{\theta\phi}, 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 \lambda_\theta 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.
