A look into mirrors: A measurement of the $\beta$-asymmetry in $^{19}$Ne decay and searches for new physics

TL;DR

This paper reports a high-precision measurement of the $eta$-asymmetry in $^{19}$Ne decay, providing constraints on the standard model and limits on new physics, including exotic tensor couplings.

Contribution

It presents the most precise measurement of $eta$-asymmetry in $^{19}$Ne decay and refines the Fermi-to-Gamow-Teller mixing ratio, supporting standard model consistency.

Findings

Consistent with previous measurements of the mixing ratio.

Supports CKM unitarity with no evidence for second class currents.

Places limits on exotic tensor couplings.

Abstract

High precision measurements of isospin $T=1/2$ decays in the neutron and nuclei provide strong model-independent constraints on extensions to the standard model of particle physics. A measurement of the $\beta$-asymmetry in $^{19}$Ne decay between the initial nuclear spin and the direction of the emitted positron is presented which establishes this decay as the most precisely characterized nuclear mirror and fixes the Fermi-to-Gamow-Teller mixing ratio to $\rho = 1.6014(+21/-28)_{sys}(8)_{stat}$. This is consistent with the previous, most precise measurement, produces a value of the CKM unitarity parameter $V_{ud}$ in agreement with the nuclear mirror, neutron and superallowed $\beta$-decay data sets, shows no evidence for second class currents, and can be effectively used with neutron decay data to place a limits on exotic tensor couplings.