# Discrepancy between experimental and theoretical $\beta$-decay rates resolved from first principles

## TL;DR

This paper resolves the long-standing discrepancy between observed and predicted $eta$-decay rates by demonstrating that the quenching arises from two-nucleon weak coupling and nuclear correlations, using advanced first-principles calculations.

## Contribution

The study provides the first comprehensive first-principles explanation for $eta$-decay rate quenching, incorporating systematic effective field theories and many-body techniques.

## Key findings

- Theoretical $eta$-decay rates align with experimental data.
- Quenching is mainly due to two-nucleon weak coupling and nuclear correlations.
- Results include accurate predictions for $^{100}$Sn decay.

## Abstract

$\beta$-decay, a process that changes a neutron into a proton (and vice versa), is the dominant decay mode of atomic nuclei. This decay offers a unique window to physics beyond the standard model, and is at the heart of microphysical processes in stellar explosions and the synthesis of the elements in the Universe. For 50 years, a central puzzle has been that observed $\beta$-decay rates are systematically smaller than theoretical predictions. This was attributed to an apparent quenching of the fundamental coupling constant $g_A \simeq $ 1.27 in the nucleus by a factor of about 0.75 compared to the $\beta$-decay of a free neutron. The origin of this quenching is controversial and has so far eluded a first-principles theoretical understanding. Here we address this puzzle and show 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 to heavy nuclei. Our results are consistent with experimental data, including the pioneering measurement for $^{100}$Sn. These theoretical advances are enabled by systematic effective field theories of the strong and weak interactions combined with powerful quantum many-body techniques. This work paves the way for systematic theoretical predictions for fundamental physics problems. These include the synthesis of heavy elements in neutron star mergers and the search for neutrino-less double-$\beta$-decay, where an analogous quenching puzzle is a major source of uncertainty in extracting the neutrino mass scale.