Charge Symmetry Breaking and Nuclear Pion Production Reactions

TL;DR

This paper explores charge symmetry breaking in nuclear pion production, focusing on theoretical calculations of asymmetry in neutron-proton reactions and developing a new framework to improve the impulse approximation in pion production models.

Contribution

It introduces a calculation of charge symmetry breaking asymmetry in np -> d pi^0 and proposes a two-body operator framework to replace the traditional impulse approximation.

Findings

Charge symmetry breaking asymmetry calculated for np -> d pi^0.

Two-body operator significantly enhances s-wave pion production.

Traditional impulse approximation is insufficient for accurate modeling.

Abstract

Large momentum transfer reactions such as pion production represent the frontier of Chiral Perturbation Theory and must be understood before more complex reactions can be considered. Pion production is also interesting in its own right, one application being the hadronic extraction of a charge symmetry breaking parameter: the contribution of the down-up quark mass difference to the neutron-proton mass difference. This dissertation reports on two primary projects: (1) a calculation of the charge symmetry breaking forward-backward asymmetry of the differential cross section of the n p -> d pi^0 reaction, and (2) the development of a new theoretical framework addressing the issue of reducibility in the impulse approximation's contribution to pion production. It is shown that the traditional one-body impulse approximation must be replaced by a two-body operator which makes a larger contribution to s-wave pion production.