Discrepancy between experimental and theoretical β-decay rates resolved from first principles

The dominant decay mode of atomic nuclei is beta decay (β-decay), a process that changes a neutron into a proton (and vice versa). This decay offers a window to physics beyond the standard model, and is at the heart of microphysical processes in stellar explosions and element synthesis in the Universe 1 – 3 . However, observed β-decay rates in nuclei have been found to be systematically smaller than for free neutrons: this 50-year-old puzzle about the apparent quenching of the fundamental coupling constant by a factor of about 0.75 (ref. 4 ) is without a first-principles theoretical explanation. Here, we demonstrate that this quenching arises to a large extent from the coupling of the weak force to two nucleons as well as from strong correlations in the nucleus. We present state-of-the-art computations of β-decays from light- and medium-mass nuclei to 100 Sn by combining effective field theories of the strong and weak forces 5 with powerful quantum many-body techniques 6 – 8 . Our results are consistent with experimental data and have implications for heavy element synthesis in neutron star mergers 9 – 11 and predictions for the neutrino-less double-β-decay 3 , where an analogous quenching puzzle is a source of uncertainty in extracting the neutrino mass scale 12 .