Electromagnetic Form Factors of Nucleon Excitations in Lattice QCD

TL;DR

This paper introduces the parity-expanded variational analysis (PEVA) technique in lattice QCD to accurately compute electromagnetic form factors of nucleon excitations at non-zero momentum, overcoming parity mixing issues.

Contribution

The paper presents a novel PEVA method that ensures consistent isolation of boosted baryon states for form factor calculations in lattice QCD.

Findings

First world-first calculations of excited state nucleon form factors.

Demonstrates effectiveness of PEVA in isolating baryon excitations.

Provides a new approach to study baryon structure at non-zero momentum.

Abstract

Variational analysis techniques in lattice QCD are powerful tools that give access to the full spectrum of QCD. At zero momentum, these techniques are well established and can cleanly isolate energy eigenstates of either positive or negative parity. In order to compute the form factors of a single energy eigenstate, we must perform a variational analysis at non-zero momentum. When we do this with baryons, we run into issues with parity mixing in the Dirac spinors, as boosted baryons are not eigenstates of parity. Due to this parity mixing, care must be taken to ensure that the projected correlation functions provided by the variational analysis correspond to the same states at zero momentum. This can be achieved through the parity-expanded variational analysis (PEVA) technique, a novel method developed at the University of Adelaide for ensuring the successful and consistent isolation of boosted baryons. Utilising this technique, we are able to compute the form factors of baryon excitations without contamination from other states. We present world-first calculations of excited state nucleon form factors using this new technique.