SPIN TRANSFER IN PP ELASTIC SCATTERING AT 198 MEV: IMPLICATIONS FOR THE PINN COUPLING CONSTANT

A precision measurement of spin transfer in $\mathrm{pp}$ elastic scattering at 197.8 MeV has been completed recently at the Indiana University Cyclotron Facility. The new data span a kinematic regime chosen specifically to maximize sensitivity to the neutral $\ensuremath{\pi}\mathrm{NN}$ coupling constant. Our results provide strong support for modern potential models of the $\mathrm{NN}$ interaction in which a relatively weak pion coupling ( ${g}_{0}^{2}\ensuremath{\approx}13.6$, ${f}_{0}^{2}\ensuremath{\approx}0.075$) is employed, but disagree significantly with predictions of older models in which ${g}_{0}^{2}\ensuremath{\approx}14.4$. Calculations in a one-boson-exchange framework indicate that most of these latter differences can be removed by reducing ${g}_{0}^{2}$ from 14.4 to 13.6 in these models.