Fundamental Symmetries

There is currently a large ongoing experimental effort at the energy, intensity, and precision frontiers to test the limits of the Standard Model of the electroweak interaction. One avenue to search for physics beyond the Standard Model consist of testing for the unitarity of the Cabibbo-Kobayashi-Maskawa matrix, which relates the quark's eigenstates under the weak interaction with its regular eigenstates. The greatest component in the unitarity test (97%) is the so-called Vud element. This element is currently determined to the greatest precision from a sample of corrected Ft-values of 14 superallowed 0+ -> 0+ pure Fermi transitions. These Ft-values requires precise and accurate knowledge of quantities including atomic masses, half-lives, and branching ratios.

Despite the great precision achieved from pure Fermi transitions, measurements in other systems remain important as conflicting results could uncover unknown systematic effects or even new physics. One such system is the superallowed mixed transitions, which can help refine the same theoretical corrections used for pure Fermi transitions and hence improve the accuracy of Vud. However, extracting Vud from these systems requires the more challenging determination of the Fermi Gamow-Teller mixing ratio, which is currently known for only five transitions. Nevertheless, it is imperative to improve the quality of other experimental data in anticipation for more measurements of the mixing ratio. To this end, several precision half-life measurements of mirror transitions have been performed at the NSL using purified radioactive ion beams from the TwinSol facility and the Notre Dame beta counting station.

Finally, we are currently developing a Paul trap that will be used for the determination of the mixing ratio through the measurement of the beta-neutrino correlation parameter. This ion trapping system, called the “Superallowed Transition Beta Neutrino Decay Ion Coincidence Trap” (St. Benedict) will be located after the TwinSol facility of the NSL. More specifically, we plan on measuring the beta-neutrino correlation parameter for the more challenging light transitions, in which the long half-lives render the measurements difficult. The more flexible beam schedule at the University of Notre Dame gives a competitive advantage to perform that type of measurement and it will allow for the determination of Vud for the lightest mirror transitions, where other interesting effects such as the possible presence of scalar current in the decay can be probed.