Determination of the Weak Axial Vector Coupling from a Measurement of the Beta-Asymmetry Parameter A in Neutron Beta Decay

TL;DR

This paper presents a precise measurement of the neutron beta-asymmetry parameter A, leading to an improved determination of the axial-vector to vector coupling ratio, which is crucial for understanding weak interactions.

Contribution

The study introduces a novel neutron polarization method and improved background reduction, significantly lowering systematic uncertainties in measuring the beta-asymmetry parameter.

Findings

Measured A_0 = -0.11996(58)

Derived coupling ratio λ = -1.2767(16)

Reduced systematic uncertainties compared to previous experiments

Abstract

We report on a new measurement of the neutron beta-asymmetry parameter $A$ with the instrument \perkeo. Main advancements are the high neutron polarization of $P = 99.7(1)%$ from a novel arrangement of super mirror polarizers and reduced background from improvements in beam line and shielding. Leading corrections were thus reduced by a factor of 4, pushing them below the level of statistical error and resulting in a significant reduction of systematic uncertainty compared to our previous experiments. From the result $A_0 = -0.11996(58)$, we derive the ratio of the axial-vector to the vector coupling constant $\lambda = g_\mathrm{A}/g_\mathrm{V} = -1.2767(16)$