Eur. Phys. J. A (2012) 48: 151
https://doi.org/10.1140/epja/i2012-12151-1

Letter

The size of the proton: Closing in on the radius puzzle

¹ Helmholtz-Institut für Strahlen- und Kernphysik and Bethe Center for Theoretical Physics, Universität Bonn, D-53115, Bonn, Germany
² Institute for Advanced Simulation and Jülich Center for Hadron Physics, Institut für Kernphysik, Forschungszentrum Jülich, D-52425, Jülich, Germany

^* e-mail: lorenzi@hiskp.uni-bonn.de

Received: 23 October 2012
Accepted: 23 October 2012
Published online: 6 November 2012

Abstract

We analyze the recent electron-proton scattering data from Mainz using a dispersive framework that respects the constraints from analyticity and unitarity on the nucleon structure. We also perform a continued fraction analysis of these data. We find a small electric proton charge radius, r _E ^p = 0.84 _−0.01 ^+0.01 fm, consistent with the recent determination from muonic hydrogen measurements and earlier dispersive analyses. We also extract the proton magnetic radius, r _M ^p = 0.86 _−0.03 ^+0.02 fm, consistent with earlier determinations based on dispersion relations.