On the strong energy dependence of the e^+e^- to ppbar amplitude near threshold

Abstract

We study the energy dependence of the e^+e^- to ppbar cross section close to the two-nucleon threshold, recently reported by the BaBar collaboration. Our analysis also includes the pbarp to e^+e^- data collected by PS170 collaboration and the e^+e^- to NNbar data from the FENICE collaboration. We show that the near-threshold enhancement in the e^+e^- to ppbar cross section can be explained by the final-state interaction between proton and antiproton in the 3S1 partial wave, utilizing the Juelich 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 presumably also driven by this final-state interaction effect. This result is in line with our previous studies of the near-threshold enhancement of the ppbar invariant mass spectrum seen in the J/Psi to gamma ppbar decay by the BES collaboration and in the B+ to ppbar K+ decay by the BaBar collaboration.