First experimental determination of the charge radius of $^{74}$Rb and its application in tests of the unitarity of the CKM matrix

TL;DR

This study used collinear-laser spectroscopy to measure the charge radius of $^{74}$Rb, providing new data that refines tests of the CKM matrix unitarity and enhances understanding of isospin symmetry breaking.

Contribution

First experimental determination of the charge radius of $^{74}$Rb, improving the isospin symmetry correction in CKM unitarity tests.

Findings

Charge radius of $^{74}$Rb measured for the first time

Hyperfine constants of $^{75}$Rb measured, confirming nuclear spin

Results impact the precision of CKM matrix unitarity tests

Abstract

Collinear-laser spectroscopy with bunched-beams technique was used for the study of neutron deficient Rb isotopes, out to $^{74}$Rb ($N=Z=37$) at TRIUMF. The measured hyperfine coupling constants of $^{76,78m}$Rb were in agreement with literature values. The nuclear spin of $^{75}$Rb was confirmed to be $I=3/2$, and its hyperfine coupling constants were measured for the first time. The mean-square charge radius of $^{74}$Rb was determined for the first time. This result has improved the isospin symmetry breaking correction term used to calculate the $\mathcal{F}t$ value, with implications for tests of the unitarity of the Cabibbo-Kobayashi-Maskawa matrix.