Polarisation in π−p → K° Λ° backward scattering at high energy

Abstract

The sign of the polarisation in backward π −p → K° Λ° high energy scattering predicted in a parameter-free Regge model with exchange degenerate Σ α − Σ γ and Σ δ − Σ β poles. The sign prediction depends on (i) the sign of the Regge phase difference between Σ α Σ γ and Σ β Σ δ , which is 90°, (ii) the [SU (3)] sign of the Y ∗ resonance couplings determined experimentally in the crossed channel KN → πΛ , (iii) the simple connection between the sign of the non-flip/flip ratio and the parity of the exchanged baryon. The large magnitude of the experimental polarisation, ⋍ 100%, is explained naturally by the 90° difference in the Regge phase and the opposite sign of j−l = ± 1 2 for Σ αΣ γ and Σ βΣ δ .