Spin independence in nucleon-nucleon scattering

Abstract

Recently, the conservation of s-channel helicity in p0 photoproduction has been confirmed experimentally by observation of the decay angular distribution in the s-channel helicity fraIne (i). Similar measurements(~) of the p0 spin-density matrix elements in the Adair frame (i.e. that rest frame of p0 in which the z-axis is given the direction of the incoming photon in the s-channel c.m.s.) showed considerable variation, thus indicating that the process obeys s-channel helicity conservation rather than spin independence. However, the spin independence model (~) generally discussed in the context of vector-meson photoproduction is not strictly identical (except in the case of scalar nucleons) with spin independence as discussed, e.g., by MANNHEIM (3) for ~d~ scattering or EISENBERG et at. (4) in the frame of an absorption model. Although there exist quark model relationships between some processes which allow one to infer that if s-channel helicity conservation holds in one process, it would also hold in the other (5), it is still a matter of considerable interest to understand the common features of various models as well as differences in their predictions. The purpose of this note is to demonstrate that, for ~A~ scattering and in the extreme high-energy limit, s-channel helicity conservation (~) and spin independence are indistinguishable if the latter is understood in the sense that T m a t r i x elements which are diagonal in the z-component of total spin dominate over off-diagonal elements at high energies. In particular, it is shown that the assumption of spin independence leads to the well-known factorization property of residues of amplitudes to which the pomeron can be coupled. This result