Abstract
We present state-of-the-art results from a lattice QCD calculation of the nucleon axial coupling, gA, using Möbius Domain-Wall fermions solved on the dynamical Nf = 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 mπ ~ {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 mπL ~ {3.22, 4.29, 5.36}. Control over all relevant sources of systematic uncertainty are demonstrated and quantified. We achieve a preliminary value of gA = 1.285(17), with a relative uncertainty of 1.33%.
Highlights
The nucleon axial coupling, gA, parameterizes the interaction strength of the nucleon with the weak axial current in the Standard Model, and is one of the fundamental properties which governs nuclear physics
The β-decay rate of a neutron to a proton is governed by the strength of gA, and confonting the sub-percent determination of gA obtained from experiments [1] with precise determination of this coupling from Lattice QCD serves as a test for the weak structure of the Standard Model
In this work we present a calculation of the nucleon axial coupling, gA = 1.285(17), based on a new computational method inspired by the Feynman-Hellmann theorem which alleviates the above concerns
Summary
Demonstration of control over all sources of systematic uncertainty related to single nucleon gA is needed before calculating precision multi-body corrections to gA. In the regime of quasielastic scattering, only coupling to a single nucleon is required, determination of the shape of the form factor from lattice QCD at high precision is desired when interpreting generation experimental results. In this work we present a calculation of the nucleon axial coupling, gA = 1.285(17), based on a new computational method inspired by the Feynman-Hellmann theorem which alleviates the above concerns. This result is commensurate with the value determined from experiment, gPADG = 1.2723(23), to a precision of 1.33%.
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