Fundamental Interactions

The Standard Model, which unifies the strong, electromagnetic and weak forces, has been remarkably successful in describing the interactions of quarks and leptons. However, the model is clearly incomplete, and it is the goal of this research program to sensitively probe its limits. Though in most cases we use the nucleus as a micro-laboratory for testing the Standard Model, the implications of the results extend far beyond nuclear physics to particle and astrophysics as well. TAMU experiments use the unique capabilities of the MARS Spectrometer and the Proton Spectrometer at the Cyclotron Institute, but also exploit the facilities at the Argonne National Laboratory, at Fermilab, and at the TRIUMF laboratory in Canada.

Nuclear reactions can be used to synthesize radioactive isotopes, but the reactions themselves are not very specific: they produce many different isotopes at one time. MARS makes it possible to analyze reaction products from the cyclotron beam, separating one synthesized isotope from all the others produced, so that one selected radioactive decay can be studied without interference from unwanted activities. In this way, we make very precise measurements on the decay of short-lived isotopes that have been specially chosen for their sensitivity to the fundamental weak interaction.

We are now measuring "superallowed" b-decay in a particular set of nuclei to test both the constancy of the weak vector coupling constant and the Standard Model's definitive predictions for quark mixing. We also use b-decay to probe for the presence of meson-exchange currents in nuclei.
The Proton Spectrometer allows us to cross-check and extend some of the b-decay results. With it, we can use charge-exchange reactions as a process equivalent to b-decay, which has the added benefit in some cases of inducing transitions that are energetically forbidden in b-decay.
Collaborative experiments are also underway using the Canadian Penning Trap (CPT) at Argonne National Laboratory. The CPT mass spectrometer is designed to set a new standard for precision in measurement of the atomic masses of unstable isotopes. Results from experiments there will tie in directly with complementary decay measurements made at the TAMU cyclotron, extending our superallowed b-decay probes of the Standard Model.