Polarization of prompt J/psi in pp -> J/psi+X at sqrt{s}=200 GeV

TL;DR

This paper calculates the production and polarization of prompt J/psi mesons in proton-proton collisions at 200 GeV using nonrelativistic QCD, predicting slight transverse polarization in forward rapidity and comparing well with experimental data.

Contribution

It provides the first detailed polarization predictions of prompt J/psi in pp collisions at this energy within the nonrelativistic QCD framework, including transverse-momentum distributions.

Findings

Predicted slight transverse polarization in forward rapidity

Good agreement with PHENIX data and NLO color-singlet model

Disagreement with LO color-singlet and s-channel-cut results

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 sqrt{s}=200 GeV. 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 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 mid-rapidity 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.