Elastic scattering and coherent single pion production in proton-helium interactions at 18.6 GeV/c

Abstract Proton-helium elastic scattering and coherent single-pion production have been studied at 18.6 GeV/ c in the four-momentum transfer region (−0.06, −0.17) GeV/ c 2 . The elastic t -distribution has a somewhat steeper slope than is predicted by the Glauber approximation. The invariant-mass distribution of the Nπ system agrees with the double Regge-pole model except at about 1.65 GeV/ c 2 where an enhancement presumably due to N ∗ resonances is seen. The model also predicts the correct magnitude of the slope for n π + α events. By using our cross sections at t ′ = −0.06 (GeV/ c ) 2 where the impulse approximation should be valid, the isospin-zero exchange elementary cross section for the n π + production is evaluated. The inelastic angular distributions are consistent with several spinparity states contributing at all Nπ masses.