The Coulomb phase revisited

Motivated by the forthcoming data from the E950 experiment at BNL for small angle polarized proton–carbon scattering we revisit the problem of Coulomb phase. The approximation usually used, with the momentum transfer squared (q2) small compared to the inverse elastic slope, is not justified within the kinematics of the E950 experiment. We go beyond this approximation and derive a new rather simple expression which recovers the formula of Bethe at small q2, but is valid at any momentum transfer.