Beta Spectrum of Unique First-Forbidden Decays as a Novel Test for Fundamental Symmetries

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.

Using a new approach for decomposing the tensor type of interactions within the multipole analysis, we represent its general coupling expression. 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. In the beta decay area, it allows us to give corrections to general orders in the finite momentum transfer, and to look at forbidden β-decays, regarding BSM physics, for the first time.

We show that the structure of the energy spectrum of emitted electrons in unique first-forbidden β-decays is sensitive to the symmetries of the weak interaction, and thus can be used as a novel probe of physics beyond the standard model. Furthermore, the energy spectrum gives constraints both in the case of right and left couplings of the new beyond standard model currents.

References

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