π−pCharge Exchange at Backward Angles

Abstract

Results of a measurement of the ${\ensuremath{\pi}}^{\ensuremath{-}}p$ charge-exchange process at backward angles are presented. Differential cross sections were measured in the angular region $\ensuremath{-}0.5<cos{\ensuremath{\theta}}^{*}<\ensuremath{-}1.0$ at incident momenta of 2, 3, 4, 5, and 6 GeV/c. An additional background subtraction to a version of the data published previously has a significant effect at 6 GeV/c and brings the data into agreement with more recent measurements. The 6-GeV/c data were combined with existing measurements of the differential cross sections for backward ${\ensuremath{\pi}}^{+}p$ and ${\ensuremath{\pi}}^{\ensuremath{-}}p$ elastic scattering to yield values for the isotopic-spin-\textonehalf{} and $\ensuremath{-}\frac{3}{2}$ $u$-channel and $s$-channel amplitudes for backward pion-nucleon scattering and for the magnitude of the phases between them. It is found that the $u$-channel amplitudes can be explained by pure Regge-pole (${\ensuremath{\Delta}}_{\ensuremath{\delta}}, {N}_{\ensuremath{\alpha}}$) exchange only near the extreme backward direction, but that a Reggeized absorption model agrees at least qualitatively with the data. The phase difference between the $I=\frac{1}{2} \mathrm{and} \frac{3}{2}$ $s$-channel amplitudes is approximately 90\ifmmode^\circ\else\textdegree\fi{} over the region $\ensuremath{-}0.8<u<0$ ${(\mathrm{G}\mathrm{e}\mathrm{V}/\mathit{c})}^{2}$.