SU(2)-Flavor-Symmetry Breaking in Nuclear Antiquark Distributions

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 $\bar u -\bar d$ distribution in nuclei in a parton recombination model. It should be noted that a finite $\bar u-\bar d$ distribution is theoretically possible in nuclei even if the sea is $SU(2)_f$ symmetric in the nucleon. In neutron-excess nuclei such as the tungsten, there exist more $d$-valence quarks than $u$-valence quarks, so that more $\bar d$-quarks are lost than $\bar u$-quarks are due to parton recombinations in the small $x$ region. Our results suggest that the nuclear modification in the tungsten is a 2--10 % effect on the $\bar u-\bar d$ distribution suggested by the NMC data. Nuclear effects on the flavor asymmetric distribution could be an interesting topic for future theoretical and experimental investigations.