CROSS-SECTIONS, SPIN OBSERVABLES, AND HELICITY AMPLITUDES OF THE PI(--]PP REACTION AT THE ISOBAR RESONANCE AND BELOW()D[)

We have calculated the pi(+)d <-> pp reaction cross sections and spin observables from threshold to the Delta resonance by considering three types of mechanisms; the impulse (absorption) mechanism, Delta rescat tering and s-wave pi N rescattering. The effect of final-state interac tions has also been included. While traditionally the first two mechan isms have been included within a sound theoretical basis, the pi N s-w ave rescattering generally has been treated phenomenologically using a pi pi NN coupling constant fitted to the low-energy pion-nucleon data . Herein, we treat the isovector component of such a pion rescattering process as being mediated by the rho-exchange. Also, in those absorpt ion mechanisms where the pion enters directly without rescattering, we employ a phenomenological cut-off scaling governed by the nucleon coo rdinates, since at the pion-nucleon vertex the nucleon itself may be o ff mass shell. The energy dependence of the total cross section is wel l explained by the combined effects of the three mechanisms, but we fi nd that this observable is not sensitive enough to give useful insight into fine details of the reaction. We calculated the spin observables of pi(+)d <-> pp at a variety of energies spanning the Delta resonanc e, finding such sensitivity to fine details of the calculation that we cannot obtain a complete agreement with the vast experimental data ba se. A better understanding of the importance of the various aspects of the reaction was obtained when the calculated helicity amplitudes wer e compared with those extracted via phase-shift analyses of the pi(+)d <-> pp reaction data.