A unique possibility of studying electromagnetic proton form factors is offered by (polarized) high energy antiprotons beams.
The measurement of the differential cross section of $\\bar p+p\\to$ $\\ell+ +\\ell^-$, $\\ell=\\mu $ or $e$ allows the
individual determination of the moduli of the electric $G_E$ and the magnetic $G_M$ form factors. Symmetry properties
based on C-invariance allow to test the reaction mechanism (one or two photon exchange) through the even property
of the cross section with respect to specific kinematical variables. Model independent properties of the observables can
be derived and a method to measure form factors (which are complex) and their relative phase is proposed.
|
