Nucleon axial coupling from Lattice QCD

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%.