Within the Standard Model, the weak nuclear interaction has a V−A structure, verified by studying correlations in the directions of the outgoing leptons in nuclear beta decays. These days, correlation measurements in nuclear beta decays are intensively studied to probe for signatures for deviations from this symmetry, originating from scalar and tensor expressions which are a-priori theoretically possible in weak interactions, and will be an indication of Beyond Standard Model (BSM) physics.

In addition, one of the present more pressing challenges in astrophysics and particle physics is understanding the nature of dark matter. One of the leading candidates which may be this material is weakly interacting massive particle (WIMP), which has spurred direct detection of dark matter via scattering of nuclei. This requires detailed knowledge about those particles' interactions with nucleons, which of course is not limited to vector type couplings only.

We develop an approach for decomposing the tensor type of interactions within the multipole analysis, and represent its general coupling expression along with the Fierz term (V-A and tensor interference). This general result can be useful for different types of BSM physics, from exotic interactions with standard particles to interactions with new particles such as those expected in the astrophysical dark matter.

Using the long wave-length reduction, we find the beta decay rates for allowed transitions and for first-forbidden unique transitions.

We show that the structure of the energy spectrum of emitted electrons in unique first-forbidden beta decays is sensitive to the tensor symmetry of the weak interaction, and thus can be used as a novel probe of physics beyond the standard model, with a number of advantages over the common correlation experimental method. At the end we summarize and present an outlook for future work.

References

Thesis under the guidance of Prof. Doron Gazit, the Hebrew University of Jerusalem

Ayala Glick-Magid, Yonatan Mishnayot, Ish Mukul, Michael Hass, Sergey Vaintraub, Guy Ron, Doron Gazit, Beta spectrum of unique first-forbidden decays as a novel test for fundamental symmetries, Phys. Lett. B767, 285 (2017), https://doi.org/10.1016/j.physletb.2017.02.023