Measurement of the Transverse Polarization of Electrons Emitted in Free Neutron Decay

TL;DR

This study measures the transverse polarization of electrons in free neutron decay, testing fundamental symmetries and constraining new physics beyond the Standard Model with high precision.

Contribution

The paper provides the first precise measurement of both components of electron transverse polarization in free neutron decay, improving limits on scalar couplings and testing time reversal symmetry.

Findings

The R coefficient is consistent with zero, indicating no T-violation.

The N coefficient agrees with Standard Model predictions.

Enhanced experimental sensitivity to potential new physics.

Abstract

Both components of the transverse polarization of electrons emitted in the beta-decay of polarized, free neutrons have been measured. The T-odd, P-odd correlation coefficient quantifying the component perpendicular to the decay plane defined by neutron polarization and electron momentum, was found to be R=0.008 +/- 0.015 +/-0.005. This value is consistent with time reversal invariance, and significantly improves limits on the relative strength of imaginary scalar couplings in the weak interaction. The value obtained for the correlation coefficient associated with the electron polarization component contained within the decay plane N=0.056 +/- 0.011 +/- 0.005, agrees with the Standard Model expectation, providing an important sensitivity test of the experimental setup.