M. Mehlman

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

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.

The β+ decay of 37K as a multi‐faceted probe of fundamental physics

Precision β decay experiments represent an important and complimentary approach to high‐energy searches for physics outside the “Standard Model”, our current understanding of fundamental particles and their interactions. The mirror decay of 37K provides an excellent probe with which to search for new physics. The ft value of this (as well as other T = 1/2 mirror transitions) can be used to provide a measurement of the value of the Vud element of the CKM mass‐mixing matrix, complementing the value obtained from superallowed pure Fermi decays. In addition, the polarized angular distribution parameters are sensitive to a variety of possible new physics: the β and ν asymmetries can be used to search for right‐handed currents in the charged weak interaction, and their energy‐dependences are sensitive to second‐class currents forbidden in the Standard Model. Time‐reversal symmetry can also be tested by a precision measurement of the triple‐vector correlation between the initial nuclear spin and the momenta of t...