Systematics in pion double charge exchange

Abstract

The initial results of a systematic investigation into pion-double-charge-exchange reactions are reported. Data consisting of angular distributions and excitation functions have been measured in an effort to determine the reaction mechanism and understand its implications for nuclear physics. Cross sections are presented for (${\ensuremath{\pi}}^{+}$,${\ensuremath{\pi}}^{\ensuremath{-}}$) reactions on $^{9}\mathrm{Be}$ $^{12,13}\mathrm{C}$, $^{16,18}\mathrm{O}$, $^{24,26}\mathrm{Mg}$, $^{32}\mathrm{S}$, and $^{209}\mathrm{Bi}$. Surprising systematics of the reaction as functions of pion scattering angle and energy, as well as target mass and isospin, are revealed. The data are discussed in terms of two reaction models, one involving a higher-order optical potential and the other involving multiple reaction amplitudes.NUCLEAR REACTIONS $^{9}\mathrm{Be}$, $^{12,13}\mathrm{C}$, $^{16,18}\mathrm{O}$, $^{24,26}\mathrm{Mg}$, $^{32}\mathrm{S}$, $^{209}\mathrm{Bi}$ (${\ensuremath{\pi}}^{+}$,${\ensuremath{\pi}}^{\ensuremath{-}}$), $E=100\ensuremath{-}300$ MeV, $\ensuremath{\theta}=5\ifmmode^\circ\else\textdegree\fi{}\ensuremath{-}33\ifmmode^\circ\else\textdegree\fi{}$; measured $\ensuremath{\sigma}(E;\ensuremath{\theta},A)$, double analog and nonanalog transitions; discuss second-order optical model, deduce two-amplitude model.