Determination of the Axial-Vector Weak Coupling Constant with Ultracold Neutrons

TL;DR

This paper reports a highly precise measurement of the neutron beta decay asymmetry using ultracold neutrons, leading to an improved determination of the axial-vector to vector weak coupling ratio.

Contribution

It provides a new, more accurate measurement of the neutron decay asymmetry and the axial-vector to vector coupling ratio using ultracold neutrons from a pulsed spallation source.

Findings

Measured decay asymmetry $A_0$ with high precision

Determined $g_A/g_V$ ratio with reduced uncertainty

Contributes to testing the Standard Model predictions

Abstract

A precise measurement of the neutron decay $\beta$-asymmetry $A_0$ has been carried out using polarized ultracold neutrons (UCN) from the pulsed spallation UCN source at the Los Alamos Neutron Science Center (LANSCE). Combining data obtained in 2008 and 2009, we report $A_0 = -0.11966 \pm 0.00089_{-0.00140}^{+0.00123}$, from which we determine the ratio of the axial-vector to vector weak coupling of the nucleon $g_A/g_V = -1.27590_{-0.00445}^{+0.00409}$.