Polarization phenomena in the reaction p+alpha -> p+pi(0)+alpha

Rekalo, MP
Tomasi-Gustafsson, E
We present a general analysis of polarization phenomena for three-body processes tin noncoplanar kinematics), in terms of a P- and T-odd acoplanarity parameter. The spin structure of the matrix element and the polarization phenomena contain new contributions, with respect to binary processes, which can be conveniently expressed as functions of this parameter. We apply this formalism to the reaction p+alpha-->p+pi (o) + alpha, in view of characterizing the different mechanisms involved and studying the, excitation of the Roper resonance. We find that the polarization transfer coefficient D-nn, where (n) over right arrow is normal to the proton scattering plane, is especially sensitive to the spin of the exchanged particle.