A unitary and analytic model of nucleon EM structure, the puzzle of JLab proton polarization data and new insight into the proton charge distribution

Abstract

The unitary and analytic model of nucleon electromagnetic structure, describing all existing nucleon form factor data, is briefly reviewed. Then in the framework of this model the problem of inconsistency of older proton electric form factor data in a space-like region (obtained from the e − p → e − p process by the Rosenbluth technique) with recent Jefferson Lab data on the ratio G E p ( t ) / G M p ( t ) (measured in a precise polarization e ⃗ − p → e − p ⃗ experiment) is suggested to be solved in favor of the latter data which, however, unlike older data imply the existence of a form factor zero, i.e. a diffraction minimum in | G E p ( t ) | around t = − Q 2 = − 13 GeV 2 . The new behavior of G E p ( t ) with the zero gives a modified proton charge distribution with an enlarged value of the mean square charge radius.