Radiative corrections to anti-neutrino proton scattering

The inverse $β$-decay reaction, $ \barν_e p \to e^+ n$, for low-energy anti-neutrinos coming from nuclear reactors is of great current interest in connection with high-precision measurements of the neutrino mixing angle $θ_13$. We have derived analytic expressions, up to next-to-leading order in heavy-baryon chiral perturbation theory, for the radiative corrections (RCs) and the nucleon-recoil corrections both for this reaction and for the related neutron $β$-decay process. We show that the recoil corrections, which include the "weak magnetism" contribution, are small for neutron $β$-decay, but for inverse $β$-decay, the recoil corrections are comparable in size to the RCs for typical energies of reactor anti-neutrinos, and they have opposite signs. The RCs and the recoil corrections exhibit very different dependences on the neutrino energy.