Light quark mass difference and isospin breaking in electromagnetic pion production

A.M. Bernstein
1998 Physics Letters B  
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 γN⃗→π N reaction is a practical reaction to measure isospin breaking in the π N system, which was
more » ... first predicted by Weinberg about 20 years ago but has never been experimentally tested.
doi:10.1016/s0370-2693(98)01257-x fatcat:bn4xuamzszbl5hlwtuowyswtry