Analysis of the Reactionπ−+p→η+nnear Threshold

We successfully fit both the total and the differential cross sections for the reaction ${\pi }^{-}+p\to \eta +n$ in the region of ${T_{\pi }}^{-}$ from threshold (558 MeV) to 900 MeV with both multichannel Breit-Wigner and effective-range formulas. We find that an $S$-wave resonance accounts for the enhancement of the reaction near threshold. A comparison is made of the various $\pi p$ $S_{11}$ phase-shift analyses with the phase shifts predicted by our multichannel fits. A search was made for the $S$-matrix poles of our Breit-Wigner and effective-range solutions on the various sheets of the energy plane.