Testing Parton Charge Symmetry at HERA

There are strong theoretical indications that the minority valence quark distributions in the nucleon may break charge symmetry by as much as 3-5%. We show that a comparison of $e^{\pm }D$ deep inelastic scattering through the charged current, for example at HERA, could provide a direct test of this effect. This measurement is also be sensitive to an intrinsic component of the strange quark sea which leads to $s\mathrm{\ne }\bar{s}$.