Nuclear structure from laser spectroscopy of light muonic atoms and ions

by Dr Randolf Pohl (Max Planck Garching)

Tuesday 4 Feb 2014, 17:00 → 18:00 Europe/Berlin

Auditorium (MPI fuer Physik)

Muonic atoms and ions are hydrogen-like systems that are formed when negative muons are stopped in ordinary matter, thereby replacing all of the atom's electrons by a single muon. The muon's Bohr radius is 200 times smaller than the corresponding electronic Bohr radius in ordinary H-like ions, due to the 200 times larger mass of the muon, compared to the electron. This results in a tremendously increased sensitivity (2003) of the muonic atom's S-states to the finite charge and magnetic radius of the nucleus. We have recently determined the proton charge radius by laser spectroscopy of the 2S-2P transition ("Lamb shift") in muonic hydrogen [1,2]. Our value of Rp=0.84087(39) fm is ten times more accurate, but 7 sigma discrepant from the world average, which is based on elastic electron-proton scattering and precision spectroscopy of regular (electronic) hydrogen. This so-called "proton radius puzzle" has sparked tremendous interest both in atomic and nuclear physics. Possile explanations range from experimental errors to unexpected behaviour of the proton and to physics beyond the Standard Model [3]. To shed new light on this discrepancy, we have measured the Lamb shift in muonic deuterium [4] and extracted a value of the charge radius of the deuteron. Currently, we are setting up an experiment to measure the Lamb shift in muonic helium ions. This will improve the accuracy of the charge radii of all helium isotopes by a factor of ten [5]. In future, spectroscopy of of muonic lithium, beryllium and boron ions may be used for significantly improved charge radius value of the lightest isotopes [6]. (*) Charge Radius Experiment using Muonic Atoms [1] R. Pohl et al. (CREMA coll.), Nature 466, 213 (2010). [2] A. Antognini et al. (CREMA coll.), Science 339, 417 (2013). [3] R. Pohl et al., Ann. Rev. Nucl. Part. Sci 63 (2013) (review in advance). [4] CREMA coll., in preparation. [5] A. Antognini et al. (CREMA coll.), Can. J. Phys. 89, 47 (2011). [6] Drake, Byer, PRA 32, 713 (1985).