Cross sections of the pp -> pp pi(0) reaction between 310 and 425 MeV

Extensive kinematically complete measurements of the pp --> pp pi (0) react ion have been made at six beam energies: 310, 320, 340, 360, 400, and 425 M eV. Angles and energies of both final-state protons are extracted from the forward detector system of the WASA-CELSIUS apparatus. Projected one-parame ter distributions of the centre-of-momentum pion angle and the angle of the two-proton relative momentum show significant deviations from isotropy. Th e slope in the pion angular distribution changes from being negative at 310 MeV to positive at 425 MeV. These distributions, and that of the two-proto n relative momentum, are described in terms of partial waves corresponding to the Ss. Ps, Pp. Sd and Ds final states. Commonly used amplitudes, derive d from their simple threshold behaviour, fail to reproduce the data at the higher energies. However, in a DWBA treatment, assuming interaction ranges related either to pi or rho exchange, we find acceptable agreement, though the longer range of pion exchange provides significantly better description of the Ps and Pp waves. (C) 2001 Elsevier Science B.V. All rights reserved .