CHIRAL PERTURBATION-THEORY AND THE PP-]PP-PI(0) REACTION NEAR-THRESHOLD

A chiral-perturbative consideration of the near-threshold pp-->pp pi(0 ) reaction indicates that the pion-rescattering term has a substantial energy and momentum dependence. The existing calculations that incorp orate this dependence give pion rescattering contributions significant ly larger than those of the conventional treatment, and this enhanced rescattering term interferes destructively with the one-body impulse t erm, leading to theoretical cross sections that are much smaller than the observed values. However, since the existing calculations are base d on coordinate-space representation, they involve a number of simplif ying assumptions about the energy-momentum flow in the rescattering di agram, even though the delicate interplay between the one-body and two -body terms makes it desirable to avoid these kinematical assumptions. We carry out here a momentum-space calculation that retains the energ y-momentum dependence of the vertices as predicted by chiral perturbat ion theory. Our improved treatment increases the rescattering amplitud e by a factor of similar to 3 over the value obtained in the r-space c alculations. The pp-->pp pi(0) transition amplitude, which is now domi nated by the rescattering term, leads to the cross section much larger than what was reported in the approximate r-space calculations. Thus, the extremely small cross sections obtained in the previous chiral pe rturbative treatments of this reaction should be considered as an acci dental consequence of the approximations employed rather than a genera l feature.