The asymmetry in π−He scattering

We show that the π⁺−³He asymmetry data obtained in a recent TRIUMF experiment at T_π = 100 MeV can be understood in terms of the elementary πN amplitudes. Through a comparison to a full optical-potential calculation that employs realistic Faddeev wave functions for the trinucleon we show that all nuclear-structure dependence cancels for at lower energies. At higher pion energies around the Δ-resonance region the sign flip of offers the possibility of extracting information about the smaller partial waves.