Testing J/psi Production and Decay Properties in Hadronic Collisions

TL;DR

This work analyzes J/psi production in hadronic collisions by focusing on J/psi produced with a balancing photon, within the color-singlet model. It derives the leptonic angular distribution in the J/psi rest frame, parameterized by four structure functions and angular coefficients A0, A1, and A2, and provides analytical results in the Collins-Soper and Gottfried-Jackson frames, showing A0 = A2 at LO. A LO parton-level calculation and Monte Carlo study assess how experimental cuts affect the observable angular distributions, illustrating that cuts can mask polarization signals but that normalization tricks (e.g., isotropic decay baselines) can help recover them. The results offer a practical framework to test J/psi production mechanisms and to probe gluon distributions via J/psi+gamma events.

Abstract

The polar and azimuthal angular distributions for the lepton pair arising from the decay of a J/psi meson produced at transverse momentum p_T balanced by a photon [or gluon] in hadronic collisions are calculated in the color singlet model (CSM). It is shown that the general structure of the decay lepton distribution is controlled by four invariant structure functions, which are functions of the transverse momentum and the rapidity of the J/psi. We found that two of these structure functions [the longitudinal and transverse interference structure functions] are identical in the CSM. Analytical and numerical results are given in the Collins-Soper and in the Gottfried-Jackson frame. We present a Monte Carlo study of the effect of acceptance cuts applied to the leptons and the photon for J/psi+ gamma production at the Tevatron.