Polarization of prompt J/psi in pp -> J/psi plus X at root s=200 GeV

Abstract

Within the framework of the nonrelativistic QCD factorization approach, we compute the cross section and polarization of prompt J/psi produced from proton-proton collisions at the center-of-momentum energy root s = 200 GeV. We present the transverse-momentum distribution in the forward-rapidity region 1.2 < vertical bar y vertical bar < 2.2 and the rapidity distribution over the transverse-momentum range 2 GeV< p(T) < 20 GeV. The perturbative contributions are computed at leading order in the strong coupling constant. We predict slight transverse polarization of J/psi in the forward-rapidity region, while that for the midrapidity region is slightly longitudinal. The transverse-momentum distribution agrees well with the PHENIX preliminary data and the color-singlet-model prediction at next-to-leading order in alpha(s), but disagrees with the result from the leading-order color-singlet model or the s-channel-cut method.