Low-energy differential cross sections of pion-proton ( pi +/-p) scattering. II. Phase shifts at T pi =32.7, 45.1, and 68.6 MeV.

We report on measurements of the differential [pi][sup [plus minus]][ital p] cross section at pion energies [ital T][sub [pi]]=32.7, 45.1, and 68.6 MeV. The measurements, covering the angular range 25[degree][le][theta][sub lab][le]123[degree], have been carried out at the Paul-Scherrer-Institute (PSI) in Villigen, Switzerland, employing the magnet spectrometer LEPS. The absolute normalization of the [pi][sup [plus minus]][ital p] cross sections have been achieved by relating them to the electromagnetic cross sections of [mu][sup [plus minus] 12]C scattering. The results are in agreement with those of our preceding measurements at [ital T][sub [pi]]=32.2 and 45.1 MeV insofar as they overlap with the region of the Coulomb nuclear interference investigated there. A comparison with the predictions of the Karlsruhe-Helsinki phase shift analysis KH80, which has formed the basis for the determination of the experimental'' [sigma] term, reveals considerable deviations. These are most pronounced for the [pi][sup +][ital p] cross sections at [ital T][sub [pi]]=32.7 and 45.1 MeV. Single energy partial wave fits result in [ital S]-wave contributions, which are about 1[degree] lower in magnitude then those specified by the KH80 solution. The data at 68.6 MeV are in good agreement with the phase shift analysis.