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

The dominant decay mode of atomic nuclei is beta decay (beta-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 beta-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 beta-decays from light- and medium-mass nuclei to Sn-100 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-beta-decay(3), where an analogous quenching puzzle is a source of uncertainty in extracting the neutrino mass scale(12).