# Wavelength-dispersive spectroscopy in the hard x-ray regime of a heavy highly-charged ion: The 1s Lamb shift in hydrogen-like gold

## TL;DR

This paper demonstrates high-resolution wavelength-dispersive spectroscopy in the hard x-ray regime to measure the 1s Lamb shift in hydrogen-like gold, showcasing a novel method for studying high-Z ions and QED effects.

## Contribution

It introduces a new spectroscopy technique using crystal optics for high-Z ions in a storage ring, enabling precise measurements of the 1s Lamb shift.

## Key findings

- First high-Z element measurement using this method
- Successful detection of the 1s Lamb shift in gold
- Paves the way for exploring higher-order QED effects

## Abstract

Accurate spectroscopy of highly charged high-Z ions in a storage ring is demonstrated to be feasible by the use of specially adapted crystal optics. The method has been applied for the measurement of the 1s Lamb shift in hydrogen-like gold (Au 78+) in a storage ring through spectroscopy of the Lyman x rays. This measurement represents the first result obtained for a high-Z element using high-resolution wavelength-dispersive spectroscopy in the hard x-ray regime, paving the way for sensitivity to higher-order QED effects.