The electromagnetic form factors of hadrons as measured both in the space
like and time like domains provide fundamental information on the nucleon
structure and internal dynamics. General expressions, including the lepton
mass, for the spin averaged differential cross section for the annihilation
reaction lepton antilepton to proton antiproton are given, as well as general
formulae for the single and double spin asymmetries. The time reversed reaction
would involve a kinematic factor. We also present general expressions for the
helicity amplitudes for this reaction.Comment: 4 pages, to be published in the Proceedings of the 17th International
Spin Physics Symposium (SPIN 2006), Kyoto, Japan; October 2-7, 200
