Measuring the phase of the nuclear scattering amplitude

The interference at small |t| of the Coulomb scattering amplitude fc and the nuclear amplitude fn is used to measure the phase of the nuclear scattering amplitude, and hence the ρ-value. The 'normal' analysis of p-bar p and pp elastic scattering uses a 'spinless' Coulomb amplitude, i.e., a Rutherford amplitude (2√π α/t) multiplied by a Coulomb form factor G2(t), an Ansatz that pretends that the nucleon does not have any magnetic scattering. The role of the anomalous magnetic moment of the nucleon, κ ∼ 1.79 is investigated. It is concluded that the current experimentally inferred values of ρ for p-bar p should be systematically lowered by ∼ 0.005-0.0100 and, correspondingly, the ρ values for pp should be systematically raised by the same amount. The theoretical uncertainties and a method of experimentally minimizing them are discussed. (author)