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

We report coincidence measurements of the (${\mathrm{\pi }}^{+}$,${\mathrm{\pi }}^0$p) reaction at a beam energy of ${\mathit{T}}_{\mathrm{\pi }}^{+}$=165 MeV. The neutral pions were detected by the LAMPF ${\mathrm{\pi }}^0$ 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 ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$ at laboratory angles ${\mathrm{\theta }}_{\mathrm{\pi }}^0$=70°, 80°, 110°, and 130°. 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 at more forward angles. Events corresponding to removal of p-shell nucleons were identified by their ${\mathrm{\pi }}^0$ and p energies. The ${\mathrm{\pi }}^0$ energy spectra for such events are compared to similar pion energy spectra for the ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$(${\mathrm{\pi }}^{\pm }$,${\mathrm{\pi }}^{\pm }$p) reactions; the cross-section ratios are consistent with ratios calculated from isospin coupling alone. ${\mathrm{\pi }}^0$ energy spectra are also compared to predictions of Δ-hole model calculations; the calculations for events in which protons are detected at the conjugate quasifree angle underestimate the (${\mathrm{\pi }}^{+}$,${\mathrm{\pi }}^0$p) cross sections by 30–55 %. At ${\mathrm{\theta }}_{\mathrm{\pi }}^0$=110° the (${\mathrm{\pi }}^{+}$,${\mathrm{\pi }}^0$p) reaction was also studied on Fe, Sn, and Pb. No significant A dependence of the cross section was observed.