Evaluation of low-Q2 fits to ep and ed elastic scattering data

Abstract

We examined several low-Q2 elastic ep and ed scattering data sets using various models to extract the proton and deuteron rms radii and developed a comprehensive algorithm for estimating the systematic bias of each extracted radius. In each case, we chose the model and upper bound for Q2 that minimized the combination of statistical uncertainty and bias. We attribute the discrepancy between small (≈0.84 fm) and large (≈0.88 fm) proton radius extractions to the absence of data that can accurately isolate the linear and quadratic contributions to the form factor at low-Q2. In light of this ambiguity, we estimated the model-dependence of each extracted radius by studying the distribution of many possible fits. The resulting radii are 0.842(4) fm for the proton and 2.092(19) fm for the deuteron. These results indicate radii consistent with those determined from muonic hydrogen and deuterium measurements.