(π+, pp) reaction on several light nuclei

The (${\pi }^{+}, 2p$) reaction has been studied on targets of ${}_{}{}^2{}_{}{}^{}\mathrm{H}$, ${}_{}{}^6{}_{}{}^{}\mathrm{Li}$, ${}_{}{}^{14}{}_{}{}^{}\mathrm{N}$, and ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$ with 70-MeV pions. All kinematical quantities needed to define completely the final state were determined. The data are presented in an unbiased form, integrated over well-defined regions in phase space, and are thus readily comparable with available theoretical calculations. Data were obtained for opening angles both on and off the kinematics of the free process, ${\pi }^{+}+d\to p+p$. Thus a more extensive test of the applicability of a pole model or impulse approximation which assumes absorption on a quasideuteron could be made. For ${}_{}{}^6{}_{}{}^{}\mathrm{Li}$ and ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$ the center of mass angular distribution was determined and compared with that for ${\pi }^{+}$ absorption on a free deuteron. Nuclear structure effects appear to play an important role for capture on ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$ and ${}_{}{}^{14}{}_{}{}^{}\mathrm{N}$, since little excitation of the low-lying levels of the residual nuclei was observed, in contrast to theoretical predictions. For events leading to low excitation of the residual nucleus, theoretical curves in recoil and relative momentum, Treiman-Yang angle, and opening angle calculated for a pole model or plane wave impulse approximation gave general agreement with the measured distributions even for events off the kinematics of the free $\pi d$ process.