Note on the electromagnetic radius of proton

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 Q2 from "0.0002 to nearly 10 GeV² for electric form factor and from "0.015 to 31 GeV² for magnetic one. Special attention was given to the small structure shown by the form factor data near "Q2=0.2 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 "Q2→0 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 "Q2. Experimental data with accuracies comparable to those of the latest data at low "Q2 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.