Observation of strong final-state effects in pi(+) production in pp collisions at 400 MeV

Differential cross sections of the reactions pp --> d pi(+) and pp --> pn p i(+) have been measured at T-p = 400 MeV by detecting the charged ejectiles in the angular range 4 degrees less than or equal to Theta(Lab) less than or equal to 21 degrees. The deduced total cross sections agree well with th ose published previously for neighbouring energies. The invariant mass spec tra are observed to be strongly affected by Delta production and NN final-s tate interaction. The data are well described by Monte Carlo simulations in cluding both these effects. The ratio of pp --> pn pi(+) and pp --> d pi(+) cross sections also compares favourably to a recent theoretical prediction which suggests a dominance of rip-production in the relative S-3(1)-state. (C) 1999 Elsevier Science B.V. All rights reserved.