Threshold pp -> pp pi(0) up to one-loop accuracy

The pp --> pp pi (0) cross section near threshold is computed up to one-loo p order including the initial and final state interactions using the hybrid heavy baryon chiral perturbation theory and the counting rule a la Weinber g. With the counter terms whose coefficients are fixed by the resonance-sat uration assumption, we find that the one-loop contributions are as importan t as the tree-order contribution and bring the present theoretical estimati on of the total cross section close to the experimental data. The short-ran ged contributions are controlled by means of a cutoff, and a mild cutoff de pendence is observed when all diagrams of the given chiral order are summed . To the order treated, however, the expansion is found to converge rather slowly, calling for further studies of the process. (C) 2001 Elsevier Scien ce B.V. All rights reserved.