Proton radius from electron-proton scattering and chiral perturbation theory

© 2017 American Physical Society. We determine the root-mean-square proton charge radius, Rp, from a fit to low-Q2 electron-proton elastic-scattering cross-section data with the higher moments fixed (within uncertainties) to the values predicted by chiral perturbation theory. We obtain Rp=0.855(11) fm. This number falls between the value obtained from muonic hydrogen analyses and the CODATA value (based upon atomic hydrogen spectroscopy and electron-proton scattering determinations).