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

TL;DR

This paper calculates charge symmetry breaking effects in the pn -> d pi0 reaction using chiral perturbation theory to extract the strong neutron-proton mass difference, confirming theoretical consistency.

Contribution

It introduces a complete leading-order calculation including a new operator to determine the strong neutron-proton mass difference from experimental data.

Findings

 MeV neutron-proton mass difference extracted

Results agree with Cottingham sum rule estimates

Provides a test of chiral QCD structure

Abstract

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. This agreement provides a non-trivial test of our current understanding of the chiral structure of QCD.