Soft gluon resummation in Drell-Yan dilepton production at small transverse momentum: spin asymmetry and a novel asymptotic formula

We discuss the double-spin asymmetry ATT (QT ) in the transversely polarized Drell-Yan process at small transverse-momentum QT of the produced dilepton. The soft gluon corrections relevant for small QT are resummed to all orders in αs, up to the next-to-leading logarithmic accuracy. We show that the soft gluon corrections largely cancel in the spin asymmetry, but the significant corrections still remain. The asymmetries ATT (QT ) are calculated for pp collision at RHIC and J-PARC, and for pp̄ collision at GSI. A novel asymptotic formula for AT T (QT ) at small QT is presented, which provides a new approach to extract the transversity δq(x) from the experimental data.