Are We Really Measuring the $\rho$-Value?

Abstract

The ``normal'' analysis of $\pbar p$ and $pp$ elastic scattering uses a `spinless' Coulomb amplitude, \ie a Rutherford amplitude ($2\sqrt{\pi}\alpha/t$) multiplied by a Coulomb form factor $G^2(t)$, an {\em ansatz} that pretends that the nucleon does not have any magnetic scattering. In this note, we investigate the role of the anomalous magnetic moment of the nucleon, $\kappa \approx 1.79$. Given the method of analysis currently used by most published experiments, we conclude that the current experimentally inferred values of $\rho$ for $\pbar p$ should be {\em systemeatically lowered} by $\approx 0.005$---0.0100 and, correspondingly, the $\rho$ values for $pp$ should be {\em systematically raised} by the same amount. We discuss the theoretical uncertainties and a method of experimentally minimizing them.