Quark contribution to charge-dependent NN interaction

Abstract

Quark contribution to the charge dependence of scattering length difference in 1 S 0 NN scattering is evaluated in a quark cluster model. Quark-mediated isospin violation mechanisms considered include, u-d mass difference, quark-exchange Coulomb interaction, QED-QCD mixing effects and pion mass difference in quark-exchange OPE interaction. We find 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 .