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 $m_{\ddot{I}}€\sim \{400,350,310,220,130\}$~MeV, three lattice spacings of $a\sim \{0.15,0.12,0.09\}$~fm, and we do a dedicated volume study with $m_{\ddot{I}}€L\sim \{3.22,4.29,5.36\}$. 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\%.

18 pages, 8 figures, Lattice 2017 Proceedings