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We report a measurement of the nuclear polarization of laser-cooled,optically-pumped $^{37}\mathrm{K}$ atoms which will allow us to preciselymeasure 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 interactionat high precision. At the TRIUMF Neutral Atom Trap (TRINAT), a magneto-opticaltrap (MOT) confines and cools neutral $^{37}\mathrm{K}$ atoms and opticalpumping spin-polarizes them. We monitor the nuclear polarization of the sameatoms that are decaying in situ by photoionizing a small fraction of thepartially polarized atoms and then use the standard optical Bloch equations tomodel their population distribution. We obtain an average nuclear polarizationof $P = 0.9913\pm0.0008$, which is significantly more precise than previousmeasurements with this technique. Since our current measurement of thebeta-asymmetry has $0.2\%$ statistical uncertainty, the polarizationmeasurement reported here will not limit its overall uncertainty. This resultalso demonstrates the capability to measure the polarization to $<0.1\%$,allowing for a measurement of angular correlation parameters to this level ofprecision, which would be competitive in searches for new physics.

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