Polarization of prompt J/ψ in pp→J/ψ+X at √s=200GeV

Within the framework of the nonrelativistic QCD factorization approach, we compute the cross section and polarization of prompt J/ψ produced from proton-proton collisions at the center-of-momentum energy √s=200GeV. We present the transverse-momentum distribution in the forward-rapidity region 1.2<|y|<2.2 and the rapidity distribution over the transverse-momentum range 2GeV<p_T<20GeV. The perturbative contributions are computed at leading order in the strong coupling constant. We predict slight transverse polarization of J/ψ 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 α_s, but disagrees with the result from the leading-order color-singlet model or the s-channel-cut method.