Charge Symmetry Breaking at TRIUMF: Past, Present, and Future

The validity of charge symmetry has long been of fundamental interest and much circumstantial evidence has accumulated over the years favoring charge symmetry breaking (CSB) on the order of a fraction of a percent. Although low energy nucleon-nucleon scattering studies have shown a slight inequality of the nn and pp scattering lengths[1], it has proved very difficult to remove experimental and theoretical uncertainties to isolate charge symmetry breaking interactions unequivocally. Evidence of CSB is present in π scattering from 3 H and 3 He and in π — d total and differential cross section measurements[2],[3],[4],[5]. The π — d results have been interpreted in terms of mass splittings in the Δ system. Differences in the binding energies of mirror nuclei (the Nolen-Schiffer effect) hint at the presence of charge symmetry breaking terms in the interaction but, again, the isolation and removal of electromagnetic (EM) effects has proved difficult[6],[7].