摘要
Hydrogen- like light muonic ions, in which one negative muonreplaces all of the electrons, are extremely sensitive probes ofnuclear structure. Using pulsed laser spectroscopy, we havemeasured three 2S- 2P transitions in the muonic helium-3(μ3He+) ion, an ion formed by a negative muon and barehelium-3 nucleus. This allowed us to extract the Lamb shift, the2P fine structure splitting, and the 2S-hyperfine splitting inμ3He+. Comparing these measurements with theory, wedetermined the root-mean-square charge radius of the helion( 3He nucleus) to be rh = 1.97007(94) fm, in good agreementwith the value from elastic electron scattering but a factor 15more accurate. Our results represent benchmarks for few-nucleon theories and open the way for precision quantumelectrodynamics tests in He atoms and ions.