Polarization of Prompt J/psi at the Tevatron

TL;DR

This paper predicts the polarization behavior of prompt J/psi particles at the Tevatron using nonrelativistic QCD, showing partial agreement with experimental data and highlighting the impact of P-wave decay contributions.

Contribution

It provides a detailed calculation of J/psi polarization within the nonrelativistic QCD framework, including the effects of radiative decays of P-wave states.

Findings

Predicted alpha parameter increases from near 0 to 0.5 as p_T rises from 5 to 20 GeV.

Prediction aligns with data at intermediate p_T but deviates at high p_T by about 3 standard deviations.

Radiative decay contributions reduce but do not eliminate transverse polarization at high p_T.

Abstract

The polarization of prompt J/psi at the Fermilab Tevatron is calculated within the nonrelativistic QCD factorization framework. The contribution from radiative decays of P-wave charmonium states decreases, but does not eliminate, the transverse polarization at large transverse momentum. The angular distribution parameter alpha for leptonic decays of the J/\psi is predicted to increase from near 0 at p_T = 5 GeV to about 0.5 at p_T = 20 GeV. The prediction is consistent with measurements by the CDF Collaboration at intermediate values of p_T, but disagrees by about 3 standard deviations at the largest values of p_T measured.