An accurate nucleon-nucleon potential with charge-independence breaking

We constructed a new NN potential, designated Argonne v18, with explicit charge-independence breaking. It supersedes our older v14 model, which was our standard nonrelativistic NN potential for most of the last decade. The main part of the new potential is charge-independent, like the old v14 model, with 14 components, each consisting of a radial function vp(r12) multiplied by an operator: 1, σ1·σ2, S12, L·S, L2, L2σ1·σ2, and (L·S)2, and each of these times τl·τ2. Three charge-dependent and one charge-asymmetric operators are added along with a complete electromagnetic interaction, resulting in a model that fits pp, np, and nn data simultaneously. The charge-dependent operators are obtained by multiplying the spin operators 1, σ1·σ2, and S12 by the isotensor T12 = 3τ1zτ2z - τ1·τ2, which differentiates between np and pp or nn T = 1 states. A major source of charge dependence in NN interactions is the mass difference of the charged and neutral pions, which is carefully treated in the new model. The charge-asymmetric operator is τ1z+τ2z which splits pp and nn states; it is constrained by the difference between nn and pp scattering lengths. The electromagnetic interaction includes Coulomb, Darwin-Foldy, vacuum polarization, and magnetic moment terms. The potential was fit directly to the Nijmegen pp and np scattering database as well as the nn scattering length and deuteron binding energy. With ∼40 adjustable parameters it gives an excellent χ2/degree of freedom of 1.09 for 4301 pp and np data in the range 0-350 MeV. A consistent set of two-body charge and current operators has also been derived to evaluate the deuteron electromagnetic form factors