Extrapolation of Proton Electromagnetic Form Factor. II

Abstract

We extrapolate the proton form factors to time-like momentum transfers to determine the spectral functions. We compare our extrapolations with preliminary measurements of the cross section for proton-antiproton annihilation into an electron-positron pair, for a time-like momentum transfer of 172 ${\mathrm{F}}^{-2\mathrm{}}$. This comparison determines an otherwise orbitrary parameter used in our conformal-transformation procedure of extrapolation. We also apply the constraint that electric and magnetic form factors are equal at time-like momentum transfer of $4M^2$. We find spectral functions with a peak around 625 MeV, a zero around 1050 MeV, and a minimum around 1500 MeV.