Extraction of the strong neutron–proton mass difference from the charge symmetry breaking in pn→dπ0

摘要

We perform a complete calculation of charge symmetry breaking effects for the reaction pn→dπ0 at leading order in chiral perturbation theory. A new leading-order operator is included. From our analysis we extract δmstr N , the strong contribution to the neutron–proton mass difference. The value obtained, δmstr N = (1.5 ± 0.8 (exp.) ± 0.5 (th.)) MeV, is consistent with the result based on the Cottingham sum rule. This agreement provides a non-trivial test of our current understanding of the chiral structure of QCD.