News From Muonic Atoms

by Aldo Antognini (ETH Zurich)

Friday 31 Oct 2014, 14:30 → 15:30 Europe/Madrid

IFAE Seminar room (IFAE)

Muonic atoms are atomic bound states of a negative muon and a nucleus. The muon, which is the 200 times heavier cousin of the electron, orbits the nucleus with a 200 times smaller Bohr radius. This enhances the sensitivity of the atomic energy levels to the nucleus finite size tremendously. By performing laser spectroscopy of the 2S-2P transitions in muonic hydrogen we have determined the proton root mean square charge radius 20 times more precisely than previously obtained. However, this value disagrees by 4 standard deviations from the value extracted from ``regular `` hydrogen spectroscopy and also by 6 standard deviations from electron-proton scattering data. The variance of the various proton radius values has led to a very lively discussion in various fields 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 yet known and the various (im)possibilities will be presented here. Here we present also preliminary results of muonic deuterium and helium-ion (He-3 and He-4) spectroscopy, which beside helping to disentangle the origin of the observed ``proton radius puzzle'' also provide values of the corresponding nuclear charge radii with high accuracy. This knowledge open the way for enhanced bound-state QED test in regular atoms and provide benchmark for few-nucleon theories.

Slides talk_antognini_barcellona.pdf