Pion-nucleon partial-wave analysis to 1100 MeV

Abstract

Comprehensive analyses of pion-nucleon elastic scattering data below 1100-MeV laboratory kinetic energy are presented. The data base from which an energy-dependent solution and 23 single-energy solutions are obtained consists of 3771 ${\ensuremath{\pi}}^{+}$p elastic, 4942 ${\ensuremath{\pi}}^{\mathrm{\ensuremath{-}}}$p elastic, and 717 ${\ensuremath{\pi}}^{\mathrm{\ensuremath{-}}}$p charge-exchange data. Partial-wave structure is characterized by the location in the complex energy plane of dominant poles and zeros, which are related to \ensuremath{\pi}-N resonances. Scattering lengths are extracted from the energy-dependent solution to characterize the low-energy behavior. We describe a method for charge-correcting ``nuclear'' amplitudes in order to use them in various charge channels; the resultant splitting between ${\ensuremath{\pi}}^{+}$p and ${\ensuremath{\pi}}^{\mathrm{\ensuremath{-}}}$p channels is necessary and sufficient to describe the data accurately. Comparison to the Karlsruhe-Helsinki analyses is favorable, although some small differences exist. We describe how the full data base and solution files can be accessed through our scattering analysis interactive dial-in (SAID) computer system at VPI, copies of which also exist at several institutions throughout the world and which can be transferred to any site with a VAX/VMS computer system. In addition to solutions presented here, SAID also encodes the Karlsruhe-Helsinki solution, the Carnegie-Mellon--Berkeley solution, and production partial waves from a recent VPI analysis. The system can be used to modify solutions, plan experiments, and obtain any of the multitude of predictions which derive from partial-wave analyses of the world data base.