Nucleon electromagnetic form factors at large momentum from Lattice QCD

TL;DR

This paper presents lattice QCD calculations of nucleon electromagnetic form factors at high momentum transfer, approaching experimental ranges, to test nonperturbative QCD predictions and compare with upcoming experimental data.

Contribution

The study provides the first lattice QCD results for nucleon form factors at high $Q^2$ up to 8 GeV$^2$, near-physical pion masses, and multiple lattice spacings, with high statistical precision.

Findings

Qualitative agreement with experimental data

Form factors and ratios studied at high $Q^2$

Flavor dependence of form factor contributions analyzed

Abstract

Proton and neutron electric and magnetic form factors are the primary characteristics of their spatial structure and have been studied extensively over the past half-century. At large values of the momentum transfer $Q^2$ they should reveal transition from nonperturbative to perturbative QCD dynamics as well as effects of quark orbital angular momenta and diquark correlations. Currently, these form factors are being measured at JLab at momentum transfer up to $Q^2=18$ GeV$^2$ for the proton and up to 14 GeV$^2$ for the neutron. We report preliminary results of our lattice calculations of these form factors, including $G_E$ and $G_M$ nucleon form factors with momenta up to $Q^2=8$ GeV$^2$, pion masses down to the almost-physical $m_\pi$=170 MeV, several lattice spacings down to $a=0.073$ fm, and high $O(10^5)$ statistics. Specifically, we study individual form factors, the $G_E/G_M$ ratios, and flavor dependence of contributions to the form factors. We observe qualitative agreement of our ab initio theory calculations with experiment. Comparison of our calculations and upcoming JLab experimental results will be an important test of nonperturbative QCD methods in the almost-perturbative regime.