Precise determination of the spin-transfer coefficient K-NN ' for np elastic scattering at 187 MeV

We have measured the normal-component spin-transfer observable K-NN' for (n ) over right arrow p elastic scattering to a precision of similar to +/- 0. 014 at 12 angles in the far-backward region (110 degrees less than or equal to theta cm less than or equal to 170 degrees) at a neutron bombarding ene rgy of 187 MeV. This kinematic regime is of particular interest in that the scattering is mediated predominantly through exchange of a single charged pion, and hence is expected to depend sensitively on the strength of the pi (+/-)NN coupling constant g(c)(2), a quantity whose precise value remains h ighly controversial. The measurements described here were carried out at th e upgraded Polarized Neutron Facility at IUCF. Details of our experimental apparatus, and the analysis procedures we employed, will be discussed, payi ng particular attention to potential sources of systematic error and their effect on the data. Our primary result is that preliminary values for K-NN' appear to agree most closely with the predictions of modern potential mode ls of the NN interaction in which a relatively weak pi NN coupling is used.