Location: TRIUMF
Participating Canadian institutions: TRIUMF, British Columbia, Manitoba
International partners: USA
TRINAT uses laser trapping and cooling techniques to study the decays of short-lived isotopes produced at ISAC, to search for new physics. Laser forces suspend the atoms in a mm-sized cloud in the center of a UHV chamber. The recoiling daughter nucleus of very low kinetic energy can freely escape. Its momentum, as well as that of the emitted beta particle can be precisely measured, permitting the reconstruction of the neutrino’s momentum, which cannot be measured directly. The angular distribution of the products of nuclear beta decay is sensitive to the Lorentz structure of the semileptonic currents, with discovery potential complementary to particle physics.
A recent development at TRINAT is the ability to optically pump the trapped atoms to a high degree (\(> 99\) % nuclear spin polarization and known to better than 0.1 %) 1. This enabled the measurement of the \(\beta\) asymmetry in \(^{37}\)K to 0.3 %, the best such measurement in any nucleus, and in agreement with the Standard Model 2.
Plans for the coming years include completing the measurement of the recoil asymmetry in spin-polarized \(^{37}\)K decay and a first time-reversal test in radiative \(\beta\) decay. An asymmetry accuracy of \(\approx 5\) % is expected, which is much more sensitive than constraints from other measurements such as the neutron radiative \(\beta\) decay branch. This period will also see the completion of a program in neutrino spectra of fission products. TRINAT has kinematically isolated the \(0^- \rightarrow 0^+\) decay branch of \(^{92}\)Rb and measured a \(\beta - \nu\) correlation, consistent with expectations. The measurement will indirectly determine whether the neutrino spectrum has non-allowed components.
A 5-fold improvement appears possible for TRINAT’s previous \(^{38m}\)K \(\beta - \nu\) correlation measurement, extending into the 2027-36 period. Isospin breaking in \(^{36}\)K will be probed, by measuring the recoil asymmetry with respect to the spin, providing a test of modern calculations needed to deduce \(V_{ud}\) from \(0^+ \rightarrow 0^+\) decay. Finally, sensitivity to parity conserving, charge-symmetry breaking time-reversal violating interactions is enhanced by \(10\times\) in the isospin-suppressed mirror decay of \(^{45}\)K over other mirror decay measurements of \(D \mathbf{I} \cdot \mathbf{v}_\beta \times \mathbf{p}_{\nu}\).