Abstract
We discuss the puzzling experimental results onbaryon-antibaryon production in e+e- annihilation close tothe threshold, in particular the fact that ≳ . We discuss aninterpretation in terms of a two-step process, via anintermediate coherent isovector state serving as an intermediarybetween e+e- and the baryon-antibaryon system. We provideevidence that the isovector channel dominates both e+e- → pions and from annihilation at rest, and showthat the observed ratio of to can be understood quantitatively inthis picture.
Highlights
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− → nn) >∼ σ(e+e− → pp)
Averaging over the available data on both the direct and time-reversed reactions, which are very consistent, and ignoring any possible variation with energy, we find: σ(e+e− → pp) σ(e+e− → nn). The fact that this ratio is less than unity requires confirmation, but even equal cross sections for e+e− → pp and e+e− → nn would be quite surprising
We recall that the ratio of the cross sections for the corresponding tchannel processes ep(n) → ep(n) should be infinite at zero momentum transfer, where the form factor measures the total proton and neutron charges, corresponding to a coherent sum over the electromagnetic charges of their constituent quarks
Summary
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− → nn) >∼ σ(e+e− → pp). Experimental data from the FENICE collaboration [1] indicate that σ(e+e− → nn) is relatively large close to threshold. This machine will yield high-precision data on baryon production in e−e+ annihilation at threshold, providing a check on the FENICE data and an accurate benchmark for testing possible theoretical explanations.
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