a Kinematically Complete Measurement of Proton Knockout by 220-MEV Pions on CARBON-12.

The nuclear reaction whereby an incident pion interacts with a nucleus, knocks out a single nucleon, and leaves the nucleus was studied. A measurement of this process can provide a stringent test of several current theoretical models of pion-nuclear interactions. The experiment was designed to obtain complete information on the final scattered particles' momenta and the thereby deduced information on the residual nucleus. The experiment was performed with 220 MeV positive and negative pion beams incident on a natural carbon target. The final pion momentum and direction of travel were measured with a magnetic spectrometer. The ejected protons' momenta were measured with a scintillator array. Measurements were taken at scattered pion angles of 61(DEGREES), 81(DEGREES), 105(DEGREES), and 127(DEGREES) for incident positive pions and at 81(DEGREES) for incident negative pions. The protons were observed at angles over the range from 15(DEGREES) to 90(DEGREES). The final particles were observed both separately and in coincidence. The excitation of the residual nucleus was calculated for the coincidence events. Differential cross sections were obtained and displayed as pion and proton energy spectra and as angular correlations. Ratios between the positive and negative pion data were made to elucidate the differences and common features of the two reactions. The data provides detailed evidence for the quasielastic picture of pion knockout reactions which is reflected in the similarity of the spectral peak energies to those seen in pion-nucleon elastic scattering. The importance of secondary processes such as pion multiple scattering and nucleon final state interactions becomes clearer with the separation of the data according to the residual nucleus excitation energy. The coincidence cross section is found to account for about half of the ((pi)('+),(pi)('+)') reaction and about half of this corresponds to quasifree knockout of the outer shell protons. For the ((pi)('-),(pi)('-)'p) reaction, the secondary processes are found to play a much more important role. The data will be valuable for future comparison with theoretical calculations.