Diffractive production of pi - pi - pi + in 200-GeV/c pi -N interactions.

Abstract

This paper analyzes ${\ensuremath{\pi}}^{\mathrm{\ensuremath{-}}}$N\ensuremath{\rightarrow}${\ensuremath{\pi}}^{\mathrm{\ensuremath{-}}}$${\ensuremath{\pi}}^{\mathrm{\ensuremath{-}}}$${\ensuremath{\pi}}^{+}$N events from Fermilab experiment E-580, using 200-GeV/c particles on a segmented target of plastic scintillator. Starting with 48 657 triggers, data-quality cuts and a cut on missing mass squared of ${M}^{2}$16 ${\mathrm{GeV}}^{2}$ lead to a final sample of 7205 events. The ${x}_{F}$ distribution of the 3\ensuremath{\pi} system shows almost all events in a sharp peak at ${x}_{F}$=1, suggesting the presence of beam diffraction into three pions. The overall t' distribution is fit to the sum of three exponential terms corresponding to coherent diffraction from carbon nuclei, diffraction from individual nucleons, and background. Cross sections per nucleon and exponential slopes are reported for each of the three components as a function of 3\ensuremath{\pi} effective mass. The cross section for diffraction from the nucleons in the target is 0.34\ifmmode\pm\else\textpm\fi{}0.04 mb/nucleon. The cross section for coherent diffraction from carbon is 1.08\ifmmode\pm\else\textpm\fi{}0.12 mb/nucleus. The exponential slope for diffraction is observed to decrease with increasing 3\ensuremath{\pi} effective mass. The fraction of coherent carbon diffraction in the total cross section is observed to decrease with increasing 3\ensuremath{\pi} effective mass. In the ${\ensuremath{\pi}}^{\mathrm{\ensuremath{-}}}$${\ensuremath{\pi}}^{+}$ effective-mass spectrum the ${\ensuremath{\rho}}^{0}$(770) and ${f}^{0}$(1270) are observed and their cross sections per nucleon are calculated. In the ${\ensuremath{\pi}}^{\mathrm{\ensuremath{-}}}$${\ensuremath{\pi}}^{\mathrm{\ensuremath{-}}}$${\ensuremath{\pi}}^{+}$ effective-mass spectrum the ${A}_{1}^{\mathrm{\ensuremath{-}}}$/${A}_{2}^{\mathrm{\ensuremath{-}}}$ and ${A}_{3}^{\mathrm{\ensuremath{-}}}$ enhancements are observed and a cross section for the ${A}_{3}^{\mathrm{\ensuremath{-}}}$ is calculated.