Seminar

News From Muonic Atoms

By
Aldo Antognini (ETH Zurich)
Date
Place
IFAE seminar room
seminar ICCUB
Muonic atoms are atomic bound states of anegative muon and a nucleus. The muon, which is the 200 times heavier cousinof the electron, orbits the nucleus with a 200 times smaller Bohr radius. This enhances the sensitivity of the atomic energy levels to the nucleus finitesize tremendously. By performing laser spectroscopy of the 2S-2Ptransitions in muonic hydrogen we have determined theproton root mean square charge radius 20 times more precisely than previouslyobtained. However, this value disagrees by 4 standard deviations from thevalue extracted from ``regular `` hydrogen spectroscopy and also by 6 standarddeviations from electron-proton scattering data. The variance of thevarious proton radius values has led to a very lively discussion in variousfields of physics: particle and nuclear physics (proton structure, new physics,scattering analysis), in atomic physics (hydrogen energy level theory,fundamental constants) and fundamental theories (bound-state problems, QED,effective field theories). The origin of this discrepancy is not yetknown and the various (im)possibilities will be presentedhere. Here we present also preliminary results of muonic deuterium and helium-ion (He-3 andHe-4) spectroscopy, which beside helping to disentangle the origin of theobserved ``proton radius puzzle'' also provide values of the correspondingnuclear charge radii with high accuracy. This knowledge open the way forenhanced bound-state QED test in regular atoms and provide benchmark forfew-nucleon theories.