SU(2)-flavor-symmetry breaking in nuclear antiquark distributions

Abstract SU (2)-flavor-symmetry breaking in antiquark distributions of the nucleon was suggested by the New Muon Collaboration (NMC) in deep inelastic muon scattering. As an independent test, Drell-Yan data for the tungsten target have been used for examining the asymmetry. We investigate whether there exists significant modification of the ū - d distribution in nuclei in a parton-recombination model. It should be noted that a finite ū - d distribution is theoretically possible in nuclei even if the sea is SU(2)f symmetric in the nucleon. In neutron-excess nuclei such as tungsten, there exist more d-valence quarks than u-valence quarks, so that more d - quarks are lost than u - quarks , due to parton-recombination s in the small x region. Our results suggest that the nuclear modification in the tungsten is a 2–10 % effect on the ū - d distribution suggested by the NMC data. Nuclear effects on the flavor asymmetric distribution could be an interesting topic for future theoretical and experimental investigations.