Nucleon axial charge in domain-wall QCD with physical mass

TL;DR

This study computes nucleon charges using domain-wall fermions at physical mass, revealing systematic deficits in axial charge and discretization errors, with implications for lattice QCD accuracy.

Contribution

First precise calculation of nucleon axial charge with domain-wall fermions at physical mass, highlighting systematic errors and nucleon signal loss in lattice QCD.

Findings

Axial charge shows a systematic deficit compared to experiment.

Vector charge exhibits possible discretization errors.

Nucleon signal diminishes around 1.1 fm from source.

Abstract

Nucleon isovector vector, $g_V$, and axialvector, $g_A$, charges calculated on a 2+1-flavor dynamical domain-wall-fermions (DWF) ensemble at physical mass jointly generated by RIKEN-BNL-Columbia (RBC) and UKQCD Collaborations with lattice cut off of 1.730(4) GeV, are reported with about a percent statistical errors, along with isovector ``scalar,'' $g_S$, and ``tensor charges,'' $g_T$, with larger statistical errors. Nucleon mass is estimated as 947(6) MeV. A few standard-deviation systematics is seen in the vector charge, likely from $O(a^2)$ discretization error through small excited-state contamination. The axialvector charge is found with a few to several standard-deviation systematic deficit, depending on calculation methods, in comparison with the experiment. Nucleon signal is likely lost as early as 10 lattice units or about 1.1 fm in time from the source.