Measurement of the transverse polarization of electrons emitted in neutron decay -- nTRV experiment

TL;DR

The nTRV experiment measured transverse electron polarization in neutron decay, setting new limits on physics beyond the Standard Model and confirming Standard Model predictions for certain correlations.

Contribution

This study provides the first measurements of transverse electron polarization components in neutron decay, improving limits on time-reversal violation and suggesting further exploration of additional correlation coefficients.

Findings

Measured the correlation coefficient R with improved limits.

Confirmed the Standard Model prediction for the N coefficient.

Highlighted the potential for future measurements of additional correlation coefficients.

Abstract

This paper recalls the main achievements of the nTRV experiment which measured two components of the transverse polarization ($\sigma_{T_{1}}$, $\sigma_{T_{2}}$) of electrons emitted in the $\beta$-decay of polarized, free neutrons and deduced two correlation coefficients, $R$ and $N$, that are sensitive to physics beyond the Standard Model. The value of time-reversal odd coefficient $R$, 0.004$\pm$0.012$\pm$0.005, significantly improved limits on the relative strength of imaginary scalar coupling constant in the weak interaction. The value obtained for the time-reversal even correlation coefficient $N$, 0.067$\pm$0.011$\pm$0.004, agrees with the Standard Model expectation, providing an important sensitivity test of the electron polarimeter. One of the conclusions of this pioneering experiment was that the transverse electron polarization in the neutron $\beta$-decay is worth more systematic exploring by measurements of yet experimentally not attempted correlation coefficients such as $H$, $L$, $S$, $U$ and $V$. This article presents a brief outlook on that questions.