Observation of Lambda -hypernuclei in the reaction 12C( pi +,K+) 1 Lambda 2C.

Abstract

The observation of $\ensuremath{\Lambda}$-hypernuclear levels in $_{\ensuremath{\Lambda}}^{12}\mathrm{C}$ by associated production through the (${\ensuremath{\pi}}^{+}, {K}^{+}$) reaction is reported. The $_{\ensuremath{\Lambda}}^{12}\mathrm{C}$ excitation-energy spectra were recorded at laboratory scattering angles of 5.6\ifmmode^\circ\else\textdegree\fi{}, 10.3\ifmmode^\circ\else\textdegree\fi{}, and 15.2\ifmmode^\circ\else\textdegree\fi{}. They show two major peaks---one attributed to the ground state, and one about 11 MeV higher. These results are compared to the strangeness-exchanging (${K}^{\ensuremath{-}}, {\ensuremath{\pi}}^{\ensuremath{-}}$) reaction. The measured cross sections are compared to relativistic distorted-wave Born-approximation calculations.