Model-independent determination of the nucleon charge radius from lattice QCD
Constantia Alexandrou, Kyriakos Hadjiyiannakou, Giannis Koutsou, Konstantin Ottnad, Marcus Petschlies
Abstract
Lattice QCD calculations of nucleon form factors are restricted to discrete values of the Euclidean four-momentum transfer. Therefore, the extraction of radii typically relies on parametrizing and fitting the lattice QCD data to obtain its slope close to zero momentum transfer. We investigate a new method, which allows to compute the nucleon radius directly from existing lattice QCD data, without assuming a functional form for the momentum dependence of the underlying form factor. The method is illustrated for the case of the isovector mean-square charge radius of the nucleon $⟨{r}_{\mathrm{isov}}^{2}⟩$ and the quark-connected contributions to $⟨{r}_{p}^{2}⟩$ and $⟨{r}_{n}^{2}⟩$ for the proton and neutron, respectively. Computations are performed using a single gauge ensemble with ${N}_{f}=2+1+1$ maximally twisted mass clover-improved fermions at physical quark mass and a lattice spacing of $a=0.08\text{ }\text{ }\mathrm{fm}$.