Abstract:
Muonic atoms place a muon in orbit just a few femtometers from the nucleus, amplifying the sensitivity of atomic energy levels to nuclear size and structure by more than two orders of magnitude. Originally conceived as a precision test of bound-state QED, muonic-atom laser spectroscopy has evolved into a transformative tool for nuclear physics. A sequence of CREMA measurements—on muonic hydrogen, deuterium, and helium isotopes—has resolved the proton-radius puzzle, established benchmark radii for the lightest nuclei, and now brings ³He–⁴He isotope-shift results into coherence. These results tightly constrain ab-initio nuclear theory, including two- and three-nucleon forces and nuclear polarizabilities. I will show how muonic spectroscopy, once aimed at QED, is now opening a powerful window into fundamental nuclear structure.