# Proton and neutron electromagnetic form factors from lattice QCD

## TL;DR

This paper presents lattice QCD calculations of proton and neutron electromagnetic form factors at physical quark masses, including disconnected contributions, to improve understanding of nucleon structure.

## Contribution

It provides the first high-precision computation of disconnected contributions to nucleon form factors at the physical point using twisted mass fermions.

## Key findings

- Disconnected contributions are non-negligible, up to 15% for neutron electric charge radius.
- Form factors, radii, and magnetic moments are determined with multiple sink-source separations.
- Results enhance understanding of nucleon electromagnetic structure from first principles.

## Abstract

The electromagnetic form factors of the proton and the neutron are computed within lattice QCD using simulations with quarks masses fixed to their physical values. Both connected and disconnected contributions are computed. We analyze two new ensembles of $N_f = 2$ and $N_f = 2 + 1 + 1$ twisted mass clover-improved fermions and determine the proton and neutron form factors, the electric and magnetic radii, and the magnetic moments. We use several values of the sink-source time separation in the range of 1.0 fm to 1.6 fm to ensure ground state identification. Disconnected contributions are calculated to an unprecedented accuracy at the physical point. Although they constitute a small correction, they are non-negligible and contribute up to 15% for the case of the neutron electric charge radius.