Precision measurement of the nuclear polarization in laser-cooled, optically pumped 37K

B Fenker ,M Anholm ,A Gorelov ,Ioana Craiciu ,M Mehlman ,D Ashery ,I Cohen ,A N Vantyghem ,Scott Smale ,Robert Anderson ,R S Behling ,John Behr ,Camille A Farfan ,John M Donohue ,K Olchanski ,H W M Norton ,J Mcneil ,D Melconian ,Olivier Thériault ,D Friesen ,Claire Warner

doi:10.1088/1367-2630/18/7/073028

Abstract

We report a measurement of the nuclear polarization of laser-cooled, optically pumped 37K atoms which will allow us to precisely measure angular correlation parameters in the -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 confines and cools neutral 37K 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 , which is significantly more precise than previous measurements with this technique. Since our current measurement of the β-asymmetry has statistical uncertainty, the polarization measurement reported here will not limit its overall uncertainty. This result also demonstrates the capability to measure the polarization to , allowing for a measurement of angular correlation parameters to this level of precision, which would be competitive in searches for new physics.

Highlights

Measurements in nuclear β-decay have historically contributed to the establishment of the standard model of electroweak physics as a theory containing massive bosons coupling only to left-handed chirality leptons
To complement high-energy searches for exotic currents in the weak interaction, these experiments should aim for a precision of ∼ 0.1% [8]. To reach this ambitious goal, we have developed the techniques at the Triumf Neutral Atom Trap (Trinat) to confine the β+-emitter, 37K (Iπ = 3/2+ → 3/2+, t1/2 = 1.2 s), in an alternating current magneto-optical trap (AC-MOT) [9, 10] and observe its decay products [11, 12]
There was no MOT or optical pumping (OP) light interacting with the atoms until the OP light was turned on at t = tOP = 332 μs

Summary

Introduction

Measurements in nuclear β-decay have historically contributed to the establishment of the standard model of electroweak physics as a theory containing massive bosons coupling only to left-handed chirality leptons. Precision measurements search for and constrain possible new physics. In isobaric analog, mixed Fermi-Gamow Teller β± decays, the angular distribution of the leptons with respect to the spin direction of the parent nucleus is sensitive to a variety of new physics including right-handed currents and scalar or tensor interactions [1, 2, 3, 4]. If we ignore this class of standard model extensions, this measurement can be combined with other measurements of isospin T = 1/2 mirror-transitions to extract the Vud element of the Cabibbo-Kobayashi-Maskawa quark mixing matrix [5, 6]. To complement high-energy searches for exotic currents in the weak interaction, these experiments should aim for a precision of ∼ 0.1% [8]

Methods

Results

Discussion

Conclusion