### Speaker

Dr
Chia Cheng Chang
(LBL)

### Description

The $\textit{axial coupling of the nucleon}$, $g_A$, is the strength of its coupling to the $\textit{weak}$ axial current of the Standard Model, much as the electric charge is the strength of the coupling to the electromagnetic current. This axial coupling dictates, for example, the rate of $\beta$-decay of neutrons to protons and the strength of the attractive long-range force between nucleons. Precision tests of the Standard Model in nuclear environments require a quantitative understanding of nuclear physics rooted in Quantum Chromodynamics, a pillar of this theory. The prominence of $g_A$ makes it a benchmark quantity to determine theoretically, a difficult task as the theory is non-perturbative. Lattice QCD provides a rigorous, non-perturbative definition of the theory which can be numerically implemented. In order to determine $g_A$, the lattice QCD community has identified two challenges which must be overcome to achieve a 2% precision by 2020: the excited state contamination must be controlled and the statistical precision must be markedly improved. Here we report a calculation of $g_A^\mathrm{QCD} = 1.271 \pm 0.013$ using an unconventional method that overcomes these challenges.

[email protected] | |

Collaboration name | CalLat |

Funding source | DOE |

### Primary author

Dr
Chia Cheng Chang
(LBL)