J Ψ decay lepton distribution in hadronic collisions

We propose the measurement of the decay angular distribution of leptons from J ψ's produced at high transverse momentum balanced by a photon [or gluon] in hadronic collisions. The polar and azimuthal angular distribution 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 ψ. We found that two of these structure functions [the longitudinal and transverse interference structure functions] are identical in the CSM. We present analytical and numerical results in the Collins-Soper and in the Gottfried-Jackson frame.