QUARK CONTRIBUTION TO CHARGE-DEPENDENT NN INTERACTION

Quark contribution to the charge dependence of scattering length diffe rence in (S0NN)-S-1 scattering is evaluated in a quark cluster model. Quark-mediated isospin violation mechanisms considered include, u-d ma ss difference, quark-exchange Coulomb interaction, QED-QCD mixing effe cts and pion mass difference in quark-exchange OPE interaction. We fin d that the total contribution of the quark effects to a(pp) - a(nn) is large and in the direction indicated by the experiments. The effects is, however, small for a(pp) - a(np).