Strangeness exchange in antiproton-proton scattering.

Abstract

A model is presented for the production of antihyperon-hyperon pairs in antiproton-proton scattering in the energy region below 2.0 GeV/c antiproton laboratory momentum accessible at CERN's Low Energy Antiproton Ring. An antibaryon-baryon potential is constructed from the Nijmegen soft-core one-boson-exchange nucleon-nucleon and hyperon-nucleon potential. Using this potential as an intermediate- and long-range interaction the multichannel Schr\"odinger equation is solved with a complex boundary condition at r=b=1.2 fm. The model is applied to the elastic p\ifmmode\bar\else\textasciimacron\fi{}p\ensuremath{\rightarrow}p\ifmmode\bar\else\textasciimacron\fi{}p scattering data, cross sections, and asymmetries at intermediate energies around 1.5 GeV/c antiproton momentum. Next we compare it to the full set of data, cross sections, polarizations, and spin correlations on the strangeness-exchange reaction p\ifmmode\bar\else\textasciimacron\fi{}p\ensuremath{\rightarrow}\ensuremath{\Lambda}\ifmmode\bar\else\textasciimacron\fi{}\ensuremath{\Lambda} which has its threshold at momentum 1435 MeV/c. Excellent results are obtained. Fitting 157 observables at 6 different energies we reach ${\mathrm{\ensuremath{\chi}}}_{\mathrm{min}}^{2}$=180.6, corresponding to ${\mathrm{\ensuremath{\chi}}}^{2}$/data = 1.15. The results demonstrate the dominance of the strangeness-changing tensor force due to the combined exchange of the K(494) and ${\mathit{K}}^{\mathrm{*}}$(892) mesons. The method of calculation is similar to the one employed in the Nijmegen partial-wave analyses of low-energy proton-proton and neutron-proton scattering data. In the same manner we perform a ``model-independent'' partial-wave analysis of the reaction p\ifmmode\bar\else\textasciimacron\fi{}p\ensuremath{\rightarrow}\ensuremath{\Lambda}\ifmmode\bar\else\textasciimacron\fi{}\ensuremath{\Lambda} close to threshold. The S-matrix elements are presented.