Nucleon Structure from Lattice QCD Using a Nearly Physical Pion Mass

TL;DR

This paper presents the first lattice QCD calculations at near-physical pion mass that accurately reproduce several nucleon structure observables, highlighting the importance of physical pion mass and excited state exclusion.

Contribution

It demonstrates that using a nearly physical pion mass and excluding excited states leads to lattice QCD results consistent with experimental data for key nucleon properties.

Findings

Accurate lattice QCD results for nucleon radii and magnetic moment

Discrepancies in axial charge calculations at low pion mass

Validation of physical pion mass importance in nucleon structure studies

Abstract

We report the first Lattice QCD calculation using the almost physical pion mass mpi=149 MeV that agrees with experiment for four fundamental isovector observables characterizing the gross structure of the nucleon: the Dirac and Pauli radii, the magnetic moment, and the quark momentum fraction. The key to this success is the combination of using a nearly physical pion mass and excluding the contributions of excited states. An analogous calculation of the nucleon axial charge governing beta decay has inconsistencies indicating a source of bias at low pion masses not present for the other observables and yields a result that disagrees with experiment.