# Hyperfine splitting in simple ions for the search of the variation of fundamental constants

## TL;DR

This paper investigates hyperfine transitions in highly charged ions to enhance sensitivity in detecting potential variations of fundamental constants like the fine-structure constant and quark masses, proposing experimental setups and analyzing achievable constraints.

## Contribution

It introduces specific heavy highly charged ions suitable for precision measurements of fundamental constant variations and discusses their potential to improve current experimental limits.

## Key findings

- Identification of ions with high sensitivity to constant variations
- Proposal of simplified spectral measurements with strong single lines
- Estimation of improved constraints on fundamental constants

## Abstract

Numerous few-electron atomic systems are considered which can be used effectively for observing a potential variation of the fine-structure constant $\alpha$ and the electron-proton mass ratio $m_e/m_p$. We examine optical magnetic dipole transitions between hyperfine-structure components in heavy highly charged H-like and Li-like ions with observably high sensitivity to a variation of $\alpha$ and $m_e/m_p$. The experimental spectra of the proposed systems consist of a strong single line, which simplifies significantly the data analysis and shortens the necessary measurement time. Furthermore, we propose systems for an experimental test of the variation of quark masses and discuss the expected level of accuracy in assessing its limitations. Finally, we establish which constraints on the variation of these fundamental constants could be provided by measurements with a hyperfine-structure highly-charged-ion clock and some reference clock, showing that a significant improvement of the current limitations can be reached.