Hypernuclear and Lambda -spin polarizations produced in the ( pi +,K+) reaction.

Abstract

Starting with the elementary amplitudes having spin-flip and spin-nonflip interactions for ${\mathrm{\ensuremath{\pi}}}^{+}$n\ensuremath{\rightarrow}\ensuremath{\Lambda}${\mathit{K}}^{+}$, hypernuclear production cross sections and polarizations have been estimated in detail for the (${\mathrm{\ensuremath{\pi}}}^{+}$,${\mathit{K}}^{+}$) reaction on available p-shell nuclear targets ${(}^{10,11}$B, $^{12,13}\mathrm{C}$, $^{14}\mathrm{N}$, $^{16}\mathrm{O}$). The experimental excitation spectra of $_{\mathrm{\ensuremath{\Lambda}}}^{12}\mathrm{C}$, $_{\mathrm{\ensuremath{\Lambda}}}^{13}\mathrm{C}$, and $_{\mathrm{\ensuremath{\Lambda}}}^{16}\mathrm{O}$, including the typical cross section data, are satisfactorily reproduced in the distorted wave impulse approximation with the configuration-mixed wave functions. The angular dependence of hypernuclear polarization is predicted for each typical state, showing, for example, that the use of the mixed wave functions changes appreciably the previous estimate with the simple one-particle--one-hole wave function for $_{\mathrm{\ensuremath{\Lambda}}}^{12}\mathrm{C}$. The \ensuremath{\Lambda}-spin polarization in nuclear medium is also estimated. Typical states are shown to have large polarizations at the hypernuclear production stage.