Extraction of the proton radius from electron-proton scattering data

We perform a new analysis of electron-proton scattering data to determine the proton electric and magnetic radii, enforcing model-independent constraints from form factor analyticity. A wide-ranging study of possible systematic effects is performed. An improved analysis is developed that rebins data taken at identical kinematic settings and avoids a scaling assumption of systematic errors with statistical errors. Employing standard models for radiative corrections, our improved analysis of the 2010 Mainz A1 Collaboration data yields a proton electric radius r_E=0.895 (20 ) fm and magnetic radius r_M=0.776 (38 ) fm . A similar analysis applied to world data (excluding Mainz data) implies r_E=0.916 (24 ) fm and r_M=0.914 (35 ) fm . The Mainz and world values of the charge radius are consistent, and a simple combination yields a value r_E=0.904 (15 ) fm that is 4 σ larger than the CREMA Collaboration muonic hydrogen determination. The Mainz and world values of the magnetic radius differ by 2.7 σ , and a simple average yields r_M=0.851 (26 ) fm . The circumstances under which published muonic hydrogen and electron scattering data could be reconciled are discussed, including a possible deficiency in the standard radiative correction model which requires further analysis.