ISOBAR PRODUCTION IN PI-P-]PI+PI-N NEAR THRESHOLD

An isobar-model partial-wave analysis of 4140 π-p→π+π-n bubble-chamber events at total center-of-mass energies between 1330 and 1380 MeV is reported. Included in the analysis is a chiral-symmetry background calculated from the phenomenological Lagrangian. Significant results of the analysis are that production is dominated by the initial P11 wave and that, in this wave, final-state εN production is more important than πΔ production. We show that the recent single-arm-spectrometer data confirm the bubble-chamber data, where the two overlap. We discuss the determination of the chiral-symmetry-breaking parameter ξ. The analysis establishes that the present data is consistent with several models of the symmetry breaking, although it favors the vector breaking model of Weinberg, ξ=0. Using a dispersion relation we show that εN production in the tail of the Roper (P11) resonance significantly affects the extraction of ξ from total-cross-section data; hence in pion production ξ cannot be determined independently of the isobar amplitudes. As a further application of the results of the analysis we determine the value of the ΔπΔ coupling constant. Our result depends on the value taken for the Δ mass and what assumptions one makes to determine the large πΔ amplitudes; but, in any case, it is considerably less than the theoretical predictions which follow from SU(6), U(12), the quark model, and superconvergence relations. We also perform, in this paper, a Goldberger-Treiman-MIT-bag-model calculation which agrees with the other theoretical predictions. We further show that by attributing all P33 inelasticity to πΔ production the results of a recent elastic-phase-shift analysis imply upper bounds on the ΔπΔ coupling constant which are consistent with the value implied by the isobar analysis. © 1979 The American Physical Society.