Spin and parity of the diffractively produced Nπ system from its interference with the Δ(1236) isobar

Abstract We perform an isospin and partial-wave analysis of the low-mass N π system in π N → π (N π ) using new data at 14 GeV/ c in the interval 0.02 t ππ 2 . We study the diffractive background by means of its interference with the Δ and find that a considerable fraction of this background has spin-parity 1 2 − and does not obey the Gribov-Morrison rule. Using a model for Δ production the helicity amplitudes for diffractive production and their phases can be estimated.