Precise 113Cd $$\beta $$ β decay spectral shape measurement and interpretation in terms of possible $$g_A$$ g A quenching

Abstract

Abstract Highly forbidden $$\beta $$ β decays provide a sensitive test to nuclear models in a regime in which the decay goes through high spin-multipole states, similar to the neutrinoless double- $$\beta $$ β decay process. There are only 3 nuclei (50V, 113Cd, 115In) which undergo a $$4^\textrm{th}$$ 4 th forbidden non-unique $$\beta $$ β decay. In this work, we compare the experimental 113Cd spectrum to theoretical spectral shapes in the framework of the spectrum-shape method. We measured with high precision, with the lowest energy threshold and the best energy resolution ever, the $$\beta $$ β spectrum of 113Cd embedded in a 0.43 kg $$\hbox {CdWO}_4$$ CdWO 4 crystal, operated over 26 days as a bolometer at low temperature in the Canfranc underground laboratory (Spain). We performed a Bayesian fit of the experimental data to three nuclear models (IBFM-2, MQPM and NSM) allowing the reconstruction of the spectral shape as well as the half-life. The fit has two free parameters, one of which is the effective weak axial-vector coupling constant, $$g_A^{\text {eff}}$$ g A eff , which resulted in $$g_A^{\text {eff}}$$ g A eff between 1.0 and 1.2, compatible with a possible quenching. Based on the fit, we measured the half-life of the 113Cd $$\beta $$ β decay including systematic uncertainties as $$7.73^{+0.60}_{-0.57} \times 10^{15}$$ 7 . 73 - 0.57 + 0.60 × 10 15 yr, in agreement with the previous experiments. These results represent a significant step towards a better understanding of low-energy nuclear processes.