Probing Charge-Symmetry-Violating Quark Distributions in Semi-Inclusive Leptoproduction of Hadrons

Recent experiments by the HERMES group at HERA are measuring semi-inclusive electroproduction of pions from deuterium. We point out that by comparing the production of $\pi^+$ and $\pi^-$ from an isoscalar target, it is possible, in principle, to measure charge symmetry violation in the valence quark distributions of the nucleons. It is also possible in the same experiments to obtain an independent measurement of the quark fragmentation functions. We review the information which can be deduced from such experiments and show the ``signature'' for charge symmetry violation in such experiments. Finally, we predict the magnitude of the charge symmetry violation, from both the valence quark distributions and the pion fragmentation function, which might be expected in these experiments.