Singleπ−Production inn−pCollisions Near Threshold

Over 4000 $n+p\to {\pi }^{-}+p+p$ events, obtained in a hydrogen bubble chamber, have been analyzed. The kinetic energies of the initiating neutrons ranged from threshold to 440 MeV. The angular distributions, correlations, and energy partition of the final-state particles as well as the excitation function are presented. They are in excellent agreement with the phenomenological theory of Gell-Mann and Watson, except for the absence in the data of a sharp peak in the momentum partition distribution near the maximum allowed ${\pi }^{-}$ momentum. The $P_s$ amplitudes account for less than 1% of the total cross section. The intensities of the various types of transitions are determined. Examples of sets of amplitudes which yield these intensities are given. However, a large number of amplitudes contribute to the cross section, and the ambiguities are too great to allow evaluation of individual amplitudes.