Alpha and helion particle charge radius difference by spectroscopy of quantum-degenerate helium

Accurate spectroscopic measurements of calculable systems provide a powerful method for testing the Standard Model and extracting fundamental constants. Recently, spectroscopic measurements of finite nuclear size effects in normal and muonic hydrogen resulted in unexpectedly large adjustments of the proton charge radius and the Rydberg constant. We measured the 2 3S → 2 1S transition frequency in a Fermi gas of 3He with an order of magnitude higher accuracy than before. Together with a previous measurement in a 4He Bose-Einstein condensate, a squared charge radius difference r2h − r2α = 1.0757(12)exp(9)theo fm2 is determined between the helion and alpha particle. This measurement provides a benchmark with unprecedented accuracy for nuclear structure calculations. A deviation of 3.6 sigma is found with a determination based on spectroscopy of muonic helium ions., , , # Dataset: Alpha and helion particle charge radius difference by spectroscopy of quantum-degenerate helium [Access this dataset on Dryad](https://doi.org/10.5061/dryad.4j0zpc8m3) This .zip folder contains the data and analysis of the 2021/2022 measurement campaign of ³He spectroscopy in a magic wavelength optical dipole trap. Contains data of atom loss spectra of degenerate Fermi gases of metastable ³He resulting from excitation along a doubly-forbidden transition at 1557nm. See main article for context and detailed explanation.\ Short summary of the contents: * raw data for individual spectra are saved per date under *analysed/Spectro*. individual loss spectra can be reconstructed by plotting the remaining number of atoms in a degenerate fermi gas (DFG) as a function of the DDS frequency which is used to scan the spectroscopy laser * using counter data in the folder *analysed/Counter* and correcting the times of different PCs with data from te folder *analysed/...,