BARYON EXCHANGES FROM U-CHANNEL FINITE-ENERGY SUM RULES

Finite-energy sum rules (FESR) are used to study the u-channel baryon Regge exchanges in πN and KN elastic scattering. The low-energy integrals over the N̄N→ππ and N̄N→K̄K cuts are evaluated by resonance saturation, including σ(0+), ρ(1-), ω(1-), A2(2+), f0(2+), ρ(3-), and ω(3-) meson poles. The integral over the πN→πN cut is evaluated in both the phase-shift and the resonance-dominance approximation, whereas resonance saturation only is used for the K̄N→K̄N and KN→KN discontinuities. The FESR integrals thus obtained are in reasonable agreement with existing Regge-exchange fits to high-energy scattering data. In particular, the following interesting results are obtained from the FESR: (i) The Nα and Λα exchange amplitudes change sign at u values appropriate to α=-12, as required by conventional Regge theory. (ii) The spin dependence of the Nα and Λα exchange amplitudes is predicted in the scattering region. (iii) The Λ exchange contributions dominate over exchange contributions in KN backward elastic scattering. © 1969 The American Physical Society.