Coincidence measurements of the (π+,π0p) reaction at Tπ+=165 MeV

We report coincidence measurements of the (pi-+,pi-0p) reaction at a beam energy of T-pi + = 165 MeV. The neutral pions were detected by the LAMPF pi-0 spectrometer and the protons by an array of plastic-scintillator telescopes. The resulting energy resolution for the determination of the excitation energy of the residual nucleus was about 10 MeV. Measurements were performed on O-16 at laboratory angles THETA-pi-0 = 70-degrees, 80-degrees, 110-degrees, and 130-degrees. The cross section is predominantly quasifree. Its angular dependence follows the trend of the free single-charge-exchange cross section at back angles and is somewhat suppressed relative to this to more forward angles. Events corresponding to removal of p-shell nucleons were identified by their pi-0 and p energies. The pi-0 energy spectra for such events are compared to similar pion energy spectra for the O-16(pi-+/-,pi-+/-p) reactions; the cross-section ratios are consistent with ratios calculated for isospin coupling alone. pi-0 energy spectra are also compared to predictions of DELTA-hole model calculations; the calculations for events in which protons are detected at the conjugate quasifree angle underestimate the (pi-0,pi-0p) cross sections by 30-55%. At THETA-pi-0 = 110-degrees the (pi-+,pi-0p) reaction was also studied on Fe, Sn, and Pb. No significant A dependence of the cross section was observed.