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

### Submission summary

 As Contributors: Kazimierz Bodek Preprint link: scipost_202103_00021v2 Date submitted: 2021-06-08 13:27 Submitted by: Bodek, Kazimierz Submitted to: SciPost Physics Proceedings Proceedings issue: DIS2021 Academic field: Physics Specialties: Nuclear Physics - Experiment Approach: Experimental

### 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.

###### Current status:
Editor-in-charge assigned

The article is meant to recall the essential results of the pioneering experiment nTRV as a base for a new project. This is why several description parts taken from original publications were only slightly modified. Figure reproduction rights were checked. The abstract has been rewritten for the most and all the Reviewer's suggestions were addressed both in the text, in figures and in the Bibliography. One more citation was added. One major question concerning the Mott vertex position distribution was answered, too.

### List of changes

1. Abstract got a new formulation.
2. The structure of the article remains unchanged.
3. Appropriate citations have been added in all reproduced Figures.
4. In Figure 1, the Mott scattering vertex was drawn in red.
5. A new citation has been added in order to clarify Figure 15.5.