Test of isospin symmetry via low energy $^1$H($\pi^-$,$\pi^o$)$n$ charge   exchange
  We report measurements of the $\pi^- p \to \pi^o n$ differential cross sections at six momenta (104-143 MeV/c) and four angles (0-40 deg) by detection of $\gamma$-ray pairs from $\pi^o \to \gamma \gamma$ 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. 
Y. Jia, T.P. Gorringe, M.D. Hasinoff, M.A. Kovash, M. Ojha, M.M.   Pavan, S. Tripathi, P.A. Zolnierczuk