Dirac and Pauli form factors from lattice QCD

We present a comprehensive analysis of the electromagnetic form factors of the nucleon from a lattice simulation with two flavors of dynamical $\mathcal{O}(a)$-improved Wilson fermions. A key feature of our calculation is that we make use of an extensive ensemble of lattice gauge field configurations with four different lattice spacings, multiple volumes, and pion masses down to $m_{\pi }\sim 180\mathrm{MeV}$. We find that by employing Kelly-inspired parametrizations for the $Q^2$ dependence of the form factors, we are able to obtain stable fits over our complete ensemble. Dirac and Pauli radii and the anomalous magnetic moments of the nucleon are extracted and results at light quark masses provide evidence for chiral nonanalytic behavior in these fundamental observables.