Nucleon axial coupling from Lattice QCD

¹ Lawrence Berkeley National Laboratory, Berkeley, CA
² University of California, Berkeley, CA
³ University of North Carolina, Chapel Hill, NC
⁴ RIKEN-BNL, Brookhaven National Laboratory, Upton, NY
⁵ Lawrence Livermore National Laboratory, Livermore, CA
⁶ Forschungszentrum Jülich, Jülich, Germany
⁷ University of Liverpool, Liverpool, UK
⁸ The College of William & Mary, Williamsburg, VA
⁹ Rutgers, Piscataway, NJ
¹⁰ University of Glasgow, Glasgow, UK
¹¹ NVIDIA Corporation, Santa Clara, CA
¹² Thomas Jefferson National Accelerator Facility, Newport News, VA

^* Speaker, e-mail: chiachang@lbl.gov

Published online: 26 March 2018

Abstract

We present state-of-the-art results from a lattice QCD calculation of the nucleon axial coupling, g_A, using Möbius Domain-Wall fermions solved on the dynamical N_f = 2 + 1 + 1 HISQ ensembles after they are smeared using the gradient-flow algorithm. Relevant three-point correlation functions are calculated using a method inspired by the Feynman-Hellmann theorem, and demonstrate significant improvement in signal for fixed stochastic samples. The calculation is performed at five pion masses of m_π ~ {400, 350, 310, 220, 130} MeV, three lattice spacings of a ~ {0.15, 0.12, 0.09} fm, and we do a dedicated volume study with m_πL ~ {3.22, 4.29, 5.36}. Control over all relevant sources of systematic uncertainty are demonstrated and quantified. We achieve a preliminary value of g_A = 1.285(17), with a relative uncertainty of 1.33%.