Precise determination of the electromagnetic form factor of the proton in the time-like region up to s = 4.2 GeV2

The s dependence of the proton form factor in the time-like region has been determined up to s = 4.2 GeV2, assuming the validity of the (G(e)) = (G(m)) = (G) hypothesis. Data were taken in a dedicated experiment performed at the LEAR antiproton ring at CERN, increasing by one order of magnitude the available statistics on the proton form factor near threshold in the time-like region. Our results consist of cross section measurements of the pBARp --> e+e- reaction for different beam momenta in the kinematical range 3.6 less-than-or-equal-to s less-than-or-equal-to 4.2 GeV2. The observed s dependence of the form factor close to threshold differs appreciably from the one suggested by previous experiments.