Elastic scattering of charged pions from 3H and 3He

We have measured the ratios of normalized yields for the elastic scattering of charged pions from ³H and³He in the backward hemisphere. At T_π=180 MeV, we have completed the angular distribution measured earlier, adding six new data points in the angular range from 119° to 169° in the π-nucleus center of mass. We also measured an excitation function with data points at T_π=142, 180, 220, and 256 MeV at the largest angle achievable with our detector-between 160° and 170° in the π-nucleus center of mass. The data, taken as a whole, show an apparent role reversal of the two charge-symmetric ratios r₁ and r₂ in the backward hemisphere. For data >=100° we observe a strong dependence of the ratios on -t, independent of T_π or θ_π. The superratio R data match very well with calculations based on the forward-hemisphere data that predict the value of the difference between the even-nucleon radii of ³H and³He. Comparisons are also made with recent calculations incorporating different wave functions and double-scattering models.