Precise determination of the proton magnetic radius from electron scattering data

Abstract

We extract the proton magnetic radius from high-precision electron-proton elastic scattering cross section data. Our theoretical framework combines dispersion analysis and chiral effective field theory and implements the dynamics governing the shape of the low-Q2 form factors. It allows us to use data up to Q2≈0.5GeV2 for constraining the radii and overcomes the difficulties of empirical fits and Q2→0 extrapolation. We obtain a magnetic radius rMp=0.850±0.001 (1σ fit uncertainty)-0.004+0.009 (full-range theory uncertainty) fm, significantly different from earlier results obtained from the same data using empirical fits, and close to our extracted electric radius rEp=0.842±0.002 (1σ fit uncertainty)-0.002+0.005 (full-range theory uncertainty) fm.