Drell–Yan double-spin asymmetry ALTALT in polarized pp¯ collisions: Wandzura–Wilczek contribution

The longitudinal-transverse spin asymmetry ALTALT in the polarized Drell–Yan process depends on the twist-3 spin-dependent distributions of nucleon. In addition to the contributions expressed as matrix element of the twist-3 operators, these distributions contain the so-called Wandzura–Wilczek part, which is completely determined by a certain integral of the twist-2 spin-dependent parton distributions. We demonstrate that the recently obtained empirical information on the transversity distribution allows a realistic estimate of the Wandzura–Wilczek contribution to ALTALT for the case of polarized proton–antiproton collisions. In particular, our results in the Wandzura–Wilczek approximation indicate that rather large ALTALT can be observed in the proposed spin experiments at GSI, and its behavior as a function of dilepton mass obeys novel pattern, compared with the other double-spin asymmetries ATTATT and ALLALL. Our results provide a guide for testing a signal of effects originating from the twist-3 operators associated with quark–gluon correlation.