Test of isospin symmetry via low-energy 1H(pi{-},pi{0})n charge exchange.

We report measurements of the π - p → π°n differential cross sections at six momenta (104-143 MeV/c) and four angles (0°-40°) by detection of γ-ray pairs from π 0 → yy decays using a photon-pair spectrometer at TRIUMF. This kinematic region exhibits a vanishing zero-degree cross section from destructive interference between s and p waves, thus yielding special sensitivity to pion-nucleon dynamics. Our data and previous data do not agree, with important implications for earlier claims of large isospin-violating effects.