We have measured differential cross sections for pion elastic scattering from ${}_{}{}^3{}_{}{}^{}\mathrm{H}$ and ${}_{}{}^3{}_{}{}^{}\mathrm{He}$ in the angular region near the minimum in the non-spin-flip amplitude. Data were acquired for incident pion energies of 180, 220, 256, and 295 MeV. Nuclear charge symmetry is investigated with the aid of several charge-symmetric ratios formed from combinations of measured cross sections. A particularly intriguing result is obtained from the superratio R, which is defined as R=dσ(${\mathrm{\pi }}^{+\mathrm{}3}$H)dσ(${\mathrm{\pi }}^{\mathrm{-}\mathrm{}3}$H)/dσ(${\mathrm{\pi }}^{+\mathrm{}3}$He)dσ(${\mathrm{\pi }}^{\mathrm{-}\mathrm{}3}$He). R is found to be greater than unity at 180 MeV and significantly smaller than unity at 256 MeV, with the transition occurring at around 210 MeV. The charge-symmetry prediction for this ratio (after allowance for the Coulomb force) is one, and is independent of energy and angle. © 1996 The American Physical Society.

• Received 10 May 1996

DOI:https://doi.org/10.1103/PhysRevC.54.2823