Measurement of the neutron decay electron-antineutrino angular correlation by the aCORN experiment

TL;DR

The aCORN experiment precisely measures the neutron decay electron-antineutrino angular correlation using a novel asymmetry method, providing results consistent across multiple runs and refining the value of the weak coupling ratio.

Contribution

This work introduces a new asymmetry-based method for measuring the neutron decay correlation coefficient with high precision.

Findings

Measured the correlation coefficient as $a = -0.10782 \

Achieved a total uncertainty of 1.7% in the correlation measurement

Determined the weak coupling ratio $\\lambda = -1.2796 \

Abstract

The aCORN experiment measures the neutron decay electron-antineutrino correlation ($a$-coefficient) using a novel method based on an asymmetry in proton time-of-flight for events where the beta electron and recoil proton are detected in delayed coincidence. We report the data analysis and result from the second run at the NIST Center for Neutron Research, using the high-flux cold neutron beam on the new NG-C neutron guide end position: $a = -0.10758 \pm 0.00136 (\mbox{stat}) \pm 0.00148 (\mbox{sys})$. This is consistent within uncertainties with the result from the first aCORN run on the NG-6 cold neutron beam. Combining the two aCORN runs we obtain $a = -0.10782 \pm 0.00124 (\mbox{stat}) \pm 0.00133 (\mbox{sys})$, which has an overall relative standard uncertainty of 1.7 \%. The corresponding result for the ratio of weak coupling constants $\lambda = G_A/G_V$ is $\lambda = -1.2796\pm 0.0062$.