The Elastic Scattering of 98 MeV Negative Pions by Hydrogen

The elastic scattering by hydrogen of negative pions with mean energy 98 MeV has been measured at 13 angles between 30° and 150° (lab.). The pion beam was monitored with a calibrated ionization chamber and its muon and electron contamination determined by means of a Cerenkov counter. This counter was also used in the scattering telescope to separate out the electrons produced by charge exchange γ-radiation. The results were corrected for Coulomb effects and a 3-parameter curve fitted to the nuclear parts. The curve is d σ/ d Ω = (1 ± 0.027) [0.385 ± 0.008 + (0.276 ± 0.015) cos θ + (0.282 ± 0.031) cos 2 θ]. Thus the forward scattering intensity is 0.942 ± 0.043 mbn sterad -1 . In a separate transmission experiment the total nuclear cross section for scattering of 98 MeV negative pions by hydrogen was found to be 21.9 ± 0.7 mbn. These two figures yield a value for the real part of the forward scattering amplitude D _ = 0.195 ± 0.006 in units h/ m π c . The corresponding value of f 2 from the dispersion relation is 0.073.