Note on the electromagnetic radius of proton

Abstract

In this paper, we have analyzed the proton form factor data by using a number of phenomenological parametrizations (models) and extracting the proton electric and magnetic radii. To this end, we performed a global fit to all available form factor data, with the virtual photon momentum squared [Formula: see text] from [Formula: see text] to nearly 10[Formula: see text]GeV2 for electric form factor and from [Formula: see text] to 31[Formula: see text]GeV2 for magnetic one. Special attention was given to the small structure shown by the form factor data near [Formula: see text][Formula: see text]GeV2. It was found that different models yield different structures with different numbers of minimum at this kinematics. Since the slope of form factor in the limit of [Formula: see text] is influenced by this structure, the extracted proton radii are consequently different for different models. Our finding recommends that future experiments should focus on this kinematics instead of low [Formula: see text]. Experimental data with accuracies comparable to those of the latest data at low [Formula: see text] would clearly help to clarify the effect of this structure on the proton charge radius. Interestingly, most of the extracted proton charge radii were found to be closer to the value obtained from the muonic hydrogen atom spectroscopy.