(p→7,π+)8Li andLi7(p→,π−)8B reactions atTp=200MeV

Angular distributions of the cross sections and analyzing powers for the ${}_{}{}^7{}_{}{}^{}\mathrm{Li}$(p,${\pi }^{\pm }$) reactions leading to the ground and first two excited states of the isobaric analog final nuclei ${}_{}{}^8{}_{}{}^{}\mathrm{Li}$ and ${}_{}{}^8{}_{}{}^{}\mathrm{B}$ have been measured at $T_{\mathrm{p}=200.4\mathrm{}}$ MeV and 199.2 MeV, respectively. The (p,${\pi }^{+}$) cross sections are an order of magnitude larger than those of the (p,${\pi }^{\mathrm{-}}$) reaction and exhibit a much stronger angular dependence. The (p,${\pi }^{+}$) analyzing power patterns are essentially state independent and similar to that of the elementary pp→d${\pi }^{+}$ reaction near threshold. The analyzing power angular distribution for the ${}_{}{}^7{}_{}{}^{}\mathrm{Li}$(p,${\pi }^{\mathrm{-}}$ ${)\mathrm{}}^8$B(2.32 MeV, $3^{+}$) transition exhibits a ‘‘signature’’ characteristic of (p,${\pi }^{\mathrm{-}}$) transitions to stretched high-spin two-particle one-hole final states, which is distinctly different from the pattern observed for transitions to low-spin final states. The differences between the two reactions are interpreted in terms of the dynamics of the elementary pp→d${\pi }^{+}$ and pn→pp${\pi }^{\mathrm{-}}$ processes.