QED confronts the radius of the proton

Recent results on muonic hydrogen (Pohl et al., 2010) [1] and the ones compiled by CODATA on ordinary hydrogen and ep-scattering (Mohr et al., 2008) [2] are 5 sigma away from each other. Two reasons justify a further look at this subject: (1) One of the approximations used in Pohl et al. (2010) [1] is not valid for muonic hydrogen. This amounts to a shift of the proton's radius by similar to 3 of the standard deviations of Pohl et al. (2010) [1], in the right direction of data-reconciliation. In field-theory terms, the error is a mismatch of renormalization scales. Once corrected, the proton radius runs, much as the QCD coupling constant does. (2) The result of Pohl et al. (2010) [1] requires a choice of the third Zemach moment. Its published independent determination is based on an analysis with a p-value - the probability of obtaining data with equal or lesser agreement with the adopted (fit form-factor) hypothesis - of 3.92 x 10(-12). In this sense, this quantity is not empirically known. Its value would regulate the level of tension between muonic- and ordinary-hydrogen results, currently at most similar to 4 sigma. There is no tension between the results of Pohl et al. (2010) [1] and the proton radius determined with help of the analyticity of its form-factors. (C) 2011 Elsevier B.V. All rights reserved.