Extraction of the strong neutron-proton mass difference from the charge symmetry breaking in pn-->d pi0

Understand

We perform a complete calculation of charge symmetry breaking effects for the reaction pn -> d pi0 at leading order in chiral perturbation theory.

• A new leading-order operator is included.
• From our analysis we extract \delta m_N^{str}, the strong contribution to the neutron-proton mass difference.
• The value obtained, \delta m_N^{str} = 1.5 \pm 0.8 (exp.) \pm 0.5 (th.) MeV, is consistent with the result based on the Cottingham sum rule.