New formalism for the nuclear Drell-Yan process

Abstract

A more systematic derivation of the new formalism for Drell-Yan processes on nuclear targets is developed by expanding the nuclear tensor in terms of the nucleon tensor. As explained previously, the new formalism which is compatible with the factorization theorem is very different from the commonly used procedure in two aspects. First, not the target-quark distribution function alone, but the product of projectile and target-quark distribution functions is convoluted with the nucleon-momentum distribution function. Second, since Drell-Yan cross sections are expressed in the centre-of-mass system, the transformation from the projectile-nucleus to-nucleon centre-of-mass systems introduces an additional nuclear effect through kinematical factors inherent in the Drell-Yan tensor. The new formulae agree with those obtained from the constituent interchange model. Using the new formalism, the nuclear effect is investigated by proton scattering off a 184W target and is found stronger than the naive expectation based on the free-nucleon target would have indicated. The difference from the conventional result is dependent both on the heavy-lepton mass and the Feynman variable.