QCD-view on hadron form factors in space-like and time-like momentum transfer regions

Abstract

QCD gives definite predictions for hadron electromagnetic form factors in space-like and time-like momentum transfer regions, such as the quark counting rules, the hypothesis of hadron helicity conservation, and the relations between nucleon and deuteron form factors in the formalism of reduced nuclear matrix elements. Recent precise data about these form factors, obtained in polarization experiments at the Jefferson Laboratory, have essentially changed our view on this subject. QCD-predictions do not apply to these data up to $Q^2$=5-6 GeV$^2$ for deuteron and for the electric form factor of proton. An analysis of these data suggests that the asymptotic region will more probably start at $Q^2$=20-25 GeV$^2$. We show that the separation of magnetic and electric proton form factors in the time-like region represents the most stringent test of the asymptotic regime and QCD-predictions.