Observation of Isobaric Analog States in Pion Single-Charge-Exchange Reactions

Abstract

Isobaric-analog-state transitions have been observed throughout the periodic table in the (${\ensuremath{\pi}}^{+}$,${\ensuremath{\pi}}^{0}$) reaction. The forward-angle differential cross sections at ${T}_{\ensuremath{\pi}}=98$ MeV on targets of C${\mathrm{H}}_{2}$, $^{7}\mathrm{Li}$, $^{13}\mathrm{C}$, $^{27}\mathrm{Al}$, $^{58}\mathrm{Ni}$, $^{90}\mathrm{Zr}$, $^{120}\mathrm{Sn}$, and $^{208}\mathrm{Pb}$ are reported. The $A$ dependence follows $(N\ensuremath{-}Z){A}^{\ensuremath{-}\frac{4}{3}}$, which is qualitatively understood in terms of a strong-absorption model. Optical-potential calculations which demonstrate the sensitivity to neutron density distributions and to the isospin dependence of higher-order dynamical effects are discussed.