Dispersion - theoretical analysis of the nucleon electromagnetic form factors : Inclusion of time – like data

We update a recent dispersion–theoretical fit to the nucleon electromagnetic form factors by including the existing data in the time–like region. We show that while the time–like data for the proton can be described consistently with the existing world space–like data, this is not the case for the neutron. Another measurement of the process e+e− → n̄n is called for. We furthermore sharpen the previous estimate of the separation between the perturbative and the non–perturbative regime, which is characterized by a scale parameter Λ2 ≃ 10GeV2. Work supported in part by the Deutsche Forschungsgemeinschaft (SFB 201) Electronic address: [email protected] Electronic address: [email protected] Address after Sept. 1, 1996: FZ Jülich, IKP (Theorie), D-52425 Jülich, Germany Electronic address: [email protected]