Proton charge radius extraction from electron scattering data using dispersively improved chiral effective field theory

Abstract

We extract the proton charge radius from the elastic form factor (FF) data using a novel theoretical framework combining chiral effective field theory and dispersion analysis. Complex analyticity in the momentum transfer correlates the behavior of the spacelike FF at finite Q2 with the derivative at Q2=0. The FF calculated in the predictive theory contains the radius as a free parameter. We determine its value by comparing the predictions with a descriptive global fit of the spacelike FF data, taking into account the theoretical and experimental uncertainties. Our method allows us to use the finite-Q2 FF data for constraining the radius (up to Q2≈0.5 GeV2 and larger) and avoids the difficulties arising in methods relying on the Q2→0 extrapolation. We obtain a radius of 0.844(7) fm, consistent with the high-precision muonic hydrogen results.