Light Quark Mass Difference and Isospin Breaking In Electromagnetic Pion Production
Abstract
It is demonstrated that there is a dynamic isospin breaking effect in the near threshold γ* N π N reaction due to the mass difference of the up and down quarks, which also causes isospin breaking in the π N system. The photopion reaction is affected through final state π N interactions (formally implemented by unitarity and time reversal invariance). It is also demonstrated that the near threshold γ N π N reaction is a practical reaction to measure isospin breaking in the π N system, which was first predicted by Weinberg about 20 years ago but has never been experimentally tested.
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