Nucleon structure from Lattice QCD using a nearly physical pion mass

We report the first Lattice QCD calculation using the almost physical pion mass m(pi) = 149MeVthat agrees with experiment for four fundamental isovector observables characterizing the gross structure of the nucleon: the Dirac and Pauli radii, the magnetic moment, and the quark momentum fraction. The key to this success is the combination of using a nearly physical pion mass and excluding the contributions of excited states. An analogous calculation of the nucleon axial charge governing beta decay has inconsistencies indicating a source of bias at low pion masses not present for the other observables and yields a result that disagrees with experiment. (C) 2014 Elsevier B. V.