# High-Resolution Hydrogen Spectroscopy and the Proton Radius Puzzle

## TL;DR

This paper discusses high-resolution hydrogen spectroscopy's role in precisely determining fundamental constants, especially the proton charge radius, and addresses the Proton Radius Puzzle with recent experimental results.

## Contribution

It reports a new precise measurement of the 1S - 3S transition in hydrogen and highlights its significance in resolving the Proton Radius Puzzle.

## Key findings

- Precise measurement of the 1S - 3S transition frequency
- Implications for the proton charge radius determination
- Contribution to the ongoing Proton Radius Puzzle investigation

## Abstract

High resolution spectroscopy of the hydrogen atom takes on particular importance in the new SI, as it allows to accurately determine fundamental constants, such as the Rydberg constant and the proton charge radius. Recently, the second most precisely measured transition frequency in hydrogen, 1S - 3S, was obtained in our group. In the context of the Proton Radius Puzzle, this result calls for further investigation.