Drell–Yan massive lepton-pairʹs angular distributions at large QT

By measuring Drell–Yan massive lepton-pairʹs angular distributions, we can identify the polarization of the virtual photon of invariant mass Q which decays immediately into the lepton-pair. In terms of a modified QCD factorization formula for Drell–Yan process, which is valid even if QT⪢Q, we calculate the massive lepton-pairʹs angular distributions at large QT. We find that the virtual photons produced at high QT are more likely to be transversely polarized. We discuss the implications of this finding to the J/ψ mesonsʹ polarization measured recently at Fermilab.