Precision measurement of the nuclear polarization in laser-cooled, optically pumped $^{37}\mathrm{K}$

TL;DR

This paper reports a highly precise measurement of nuclear polarization in laser-cooled $^{37}$K atoms, enabling more accurate tests of the weak interaction and potential new physics through beta-decay angular correlations.

Contribution

The study introduces a novel, highly precise method for measuring nuclear polarization in laser-cooled atoms, surpassing previous techniques in accuracy.

Findings

Achieved an average nuclear polarization of 0.9913±0.0008.

Demonstrated the capability to measure polarization to less than 0.1%.

Confirmed that polarization measurement will not limit beta-decay asymmetry experiments.

Abstract

We report a measurement of the nuclear polarization of laser-cooled, optically-pumped $^{37}\mathrm{K}$ atoms which will allow us to precisely measure angular correlation parameters in the beta-decay of the same atoms. These results will be used to test the $V-A$ framework of the weak interaction at high precision. At the TRIUMF Neutral Atom Trap (TRINAT), a magneto-optical trap (MOT) confines and cools neutral $^{37}\mathrm{K}$ atoms and optical pumping spin-polarizes them. We monitor the nuclear polarization of the same atoms that are decaying in situ by photoionizing a small fraction of the partially polarized atoms and then use the standard optical Bloch equations to model their population distribution. We obtain an average nuclear polarization of $P = 0.9913\pm0.0008$, which is significantly more precise than previous measurements with this technique. Since our current measurement of the beta-asymmetry has $0.2\%$ statistical uncertainty, the polarization measurement reported here will not limit its overall uncertainty. This result also demonstrates the capability to measure the polarization to $<0.1\%$, allowing for a measurement of angular correlation parameters to this level of precision, which would be competitive in searches for new physics.