Spin correlations inp→p→→pnπ+pion production near threshold

Abstract

A first measurement of longitudinal as well as transverse spin correlation coefficients for the reaction $\stackrel{\ensuremath{\rightarrow}}{p}\stackrel{\ensuremath{\rightarrow}}{p}\ensuremath{\rightarrow}\mathrm{pn}{\ensuremath{\pi}}^{+}$ is made using a polarized proton target and a polarized proton beam. We report kinematically complete measurements for this reaction at 325-, 350-, 375-, and 400-MeV beam energies. The spin correlation coefficients ${A}_{\mathrm{xx}}{+A}_{\mathrm{yy}},$ ${A}_{\mathrm{xx}}\ensuremath{-}{A}_{\mathrm{yy}},$ ${A}_{\mathrm{zz}},$ and ${A}_{\mathrm{xz}}$ and the analyzing power ${A}_{y},$ as well as angular distributions for $\ensuremath{\sigma}({\ensuremath{\theta}}_{\ensuremath{\pi}})$ and the polarization observables ${A}_{\mathrm{ij}}({\ensuremath{\theta}}_{\ensuremath{\pi}}),$ are extracted. Partial wave cross sections for dominant transition channels are obtained from a partial-wave analysis that included transitions with final-state angular momenta of $l<~1.$ The measurements of the $\stackrel{\ensuremath{\rightarrow}}{p}\stackrel{\ensuremath{\rightarrow}}{p}\ensuremath{\rightarrow}\mathrm{pn}{\ensuremath{\pi}}^{+}$ polarization observables are compared with the predictions from the J\"ulich meson exchange model. The agreement is very good at 325 MeV, but it deteriorates increasingly for the higher energies. At all energies agreement with the model is better than for the reaction $\stackrel{\ensuremath{\rightarrow}}{p}\stackrel{\ensuremath{\rightarrow}}{p}\ensuremath{\rightarrow}\mathrm{pp}{\ensuremath{\pi}}^{0}.$