Hunting for an EMC–like effect for antiquarks

Abstract

We argue that the Drell–Yan process in the xA≥0.15 kinematics recently studied at FNAL by the E906/SeaQuest experiment may allow to observe an analogous of the EMC effect for antiquarks. The effects of Fermi motion and energy loss are considered. The preliminary E906/SeaQuest data are inconsistent with the growth of the σA/AσN ratio expected in the Fermi motion scenario at xA≥0.25. The pattern of the xA dependence of the ratio seems also inconsistent with a scenario in which the dominant nuclear effect is a suppression of the cross section due to the energy loss experienced by a quark of the projectile proton involved in the Drell–Yan process. All together the data suggest the possibility of a modification of the antiquark parton distributions in nuclei, with a pattern similar to the one observed in the EMC effect. We argue that optimal kinematics to look for an antiquark EMC–like effect would be to measure the σADY/AσNDY ratios for xA = 0.2 – 0.4 and xp ≈ constant.