On the strong energy dependence of the e+ e-⇆ p(p)over-bar amplitude near threshold

We study the energy dependence of the e(+)e(-) -> p (k) over bar cross section close to the two-nucleon threshold, recently reported by the BaBar Collaboration. Our analysis also includes the (p) over barp -> e(+)e(-) data collected by PS170 Collaboration and the e(+)e(-) -> N (K) over bar data from the FENICE Collaboration. We show that the near-threshold enhancement in the e(+)e(-) ->. pp cross section can be explained by the final-state interaction between proton and antiproton in the S-3(1) partial wave, utilizing the Julich nucleon-antinucleon model. As a consequence, the strong dependence of the proton electromagnetic form factors on the momentum transfer close to the two-nucleon threshold is then likewise driven by this final-state interaction effect. This result is in line with our previous studies of the near-threshold enhancement of the pp invariant mass spectrum seen in the J/psi -> gamma p (p) over bar decay by the BES Collaboration and in the B+ -> p (p) over barK(+) decay by the BaBar Collaboration. (c) 2006 Elsevier B.V. All rights reserved.