We report measurements of the π−p→πon differential cross
sections at six momenta (104-143 MeV/c) and four angles (0-40 deg) by detection
of γ-ray pairs from πo→γγ decays using the TRIUMF
RMC spectrometer. This region exhibits a vanishing zero-degree cross section
from destructive interference between s-- and p--waves, thus yielding special
sensitivity to pion-nucleon dynamics and isospin symmetry breaking. Our data
and previous data do not agree, with important implications for earlier claims
of large isospin violating effects in low energy pion-nucleon interactions.Comment: 5 pages, 3 figures, submitted to Physical Review Letter