Analyzing power forπ−pcharge exchange in the backward hemisphere from 301 to 625 MeV/cand a test ofπNpartial-wave analyses

The analyzing power of ${\pi }^{-}p\to {\pi }^{0}n$ has been measured for $p_{\pi }=301-625\mathrm{}$ MeV/c with a transversely polarized target, mainly in the backward hemisphere. The final-state neutron and a $\gamma$ from the ${\pi }^0$ were detected in coincidence with two counter arrays. Our results are compared with predictions of recent $\pi N$ partial-wave analyses by the groups of Karlsruhe-Helsinki, Carnegie-Mellon University-Lawrence Berkeley Laboratory (CMU-LBL), and Virginia Polytechnic Institute (VPI). At the lower incident energies little difference is seen among the three analyses, and there is excellent agreement with our data. At 547 MeV/c and above, our data strongly favor the VPI phases, and disagree with Karlsruhe-Helsinki and CMU-LBL analyses, which are the source of the $\pi N$ resonance parameters given in the Particle Data Group table.