Shrinking the Proton – Laser spectroscopy of muonic atoms an ions
Prof. Dr. Randolf Pohl (Institut für Physik, Universität Mainz)

In muonic atoms, the atomic electrons are replaced by a single muon. Due to the large muon mass and correspondingly tiny Bohr orbit, nuclear structure effects are vastly enhanced.

We have performed laser spectroscopy on muonic hydrogen, deuterium, and helium-3 and -4 ions, with surpising results. Our value of the proton and deuteron charge radii are, for example, 5-6 standard deviations smaller than the corresponding world averages from regular atoms and electron scattering.

I will discuss the so-called "proton radius puzzle", report on more measurements in muonic atoms, and the result of a new measurement in regular atomic hydrogen.