Analyzing power forπ−p elastic scattering in the energy region of the Roper resonance

High-precision measurements of the analyzing power $A_N$ in ${\pi }^{\mathrm{-}}$p elastic scattering at $p_{\pi }$=471–687 MeV/c are presented and compared with the results of recent πN partial-wave analyses (PWA’s) by the Karlsruhe-Helsinki, CMU-LBL, and VPI groups. While agreeing with the main features of the measured angular dependence of $A_N$, the three PWA’s yield larger values than the measurements at forward angles at $p_{\pi }$=471, 547, and 625 MeV/c. At 687 MeV/c the PWA’s do not agree with the data at far backward angles. We estimate the effect of our data on the phase shifts in this energy region, which includes the Roper resonance.