SAIP2026

Investigating Gamow–Teller β-decays using pn-QRPA framework

8 Jul 2026, 12:20

20m

Lecture Hall GH2 (University of the Western Cape)

Oral Presentation Track B - Nuclear, Particle and Radiation Physics Nuclear, Particle and Radiation Physics -1

Speaker

Mr Odwa Tyuka (University of the Western Cape)

Description

Investigations of weak interactions through Gamow-Teller (GT) β-decays
play an important role in neutrino physics, astrophysics and studies of fundamental symmetries [1–3]. Because these decays happen within nuclei, nuclear-effects significantly influence the decay rates. These effects are incorporated in calculated nuclear matrix elements (NMEs), which convey information about the initial and the final state of the decay as well as the transition operator. For this reason, it is essential to describe GT NMEs accurately. However, a long-standing and unresolved problem is that theoretical models tend to overestimate GT NMEs compared to experimental data. This discrepancy is usually resolved by the “quenching” of the axial-vector coupling constant (gA), which is essentially the requirement of an effective gA that is smaller than the free-nucleon value [4, 5].

Recently, Ejiri and Suhonen [6] introduced a different approach to study gA quenching, based on the study of pairs of mirror-like β+ and β− transitions between even–even and odd–odd nuclei. They showed that many model uncertainties, such as those associated with pairing effects and the dependence on the particle-particle interaction strength (gpp) could be reduced. Despite this progress, it is still unclear whether the required quenching arises from limitations in nuclear structure models or from more fundamental modifications of the axial current in the nuclear medium. In this work, we address this problem by performing proton-neutron Quasiparticle Random Phase Approximation (pn-QRPA) calculations of GT transitions for selected nuclei, to study the dependence of NMEs on gpp, in addition to calculating magnetic dipole (M1) transition strengths. A systematic comparison between theoretical and experimental M1 strengths is used to test the accuracy of the model predictions and to investigate correlations between GT and M1 matrix elements.

References

[1] J.D Vergados, H Ejiri, and F. Simkovic. Theory of neutrinoless double-betadecay. Reports on Progress in Physics, 75(10):106301, 2012

[2] H. Ejiri. Nuclear spin isospin responses for low-energy neutrinos. Physics Reports, 338(3):265–351, 2000.

[3] F.F Deppisch, J. Harz, W. Huang, M. Hirsch, and H. P¨as. Falsifying high-scale baryogenesis with neutrinoless double beta decay and lepton flavor violation. Physical Review D, 92(3):036005, 2015.

[4] B.A Brown and B.H Wildenthal. Status of the nuclear shell model. Annual Review of Nuclear and Particle Science, 38(1):29–66, 1988.

[5] J.T Suhonen. Value of the axial-vector coupling strength in β and ββ decays: A review. Frontiers in Physics, 5:55, 2017.

[6] H. Ejiri and J. Suhonen. GT neutrino–nuclear responses for double beta
decays and astro neutrinos. Journal of Physics G: Nuclear and Particle Physics, 42(5):055201, 2015