On electron-positron annihilation into nucleon-antinucleon pairs

We discuss the puzzling experimental results on baryon-antibaryon production in e⁺e^- annihilation close to the threshold, in particular the fact that σ(e⁺e^- → n̄n) ≳ σ(e⁺e^- → p̄p). We discuss an interpretation in terms of a two-step process, via an intermediate coherent isovector state serving as an intermediary between e⁺e^- and the baryon-antibaryon system. We provide evidence that the isovector channel dominates both e⁺e^- → pions and from N̄N annihilation at rest, and show that the observed ratio of σ(e ⁺e^- → n̄n) to σ(e⁺e^- → p̄p) can be understood quantitatively in this picture.