Role of the pi N P11 interaction in pi d elastic scattering at 50 MeV.

Measurements of the vector analyzing power {ital iT}{sub 11} in {pi}{sup +}{ital d} elastic scattering at 50 MeV have been made at pion laboratory scattering angles between 60{degree} and 130{degree} using a dynamically polarized target and a magnetic spectrometer. In contrast to measurements of spin observables at higher energies, we find agreement with models that include the {pi}{ital N} {ital P}{sub 11} amplitude and disagreement with models that exclude or suppress it.