A higher-order calculation of np scattering in cut-off effective field theory

Abstract We report a next-to-leading-order (NLO) chiral perturbation theory calculation of the neutron-proton scattering cross section in the 1 S 0 channel using a cut-off regularization. The inclusion of two-pion exchanges in the irreducible diagrams – or potential – figuring at NLO is found to be important in enlarging the domain of validity of the effective field theory. We are able to reproduce the scattering phase shift data up to p=300 MeV, with an agreement which is superior to results of other effective field theory approaches. We also discuss the importance of the explicit pion degree of freedom in scattering process.