Laser spectroscopy of muonic deuterium: New contribution to the proton puzzle

We report the first laser spectroscopy of muonic deuterium. At the Paul Scherrer Institute, we have measured the frequency of the 2S-2P Lamb shift in muonic deuterium. As in the case of the muonic hydrogen, the observed lines are shifted from the theoretical predictions. Thanks to improved new QED and nuclear structure calculations, an accurate determination of the deuteron radius can be extracted from our study. This determination will give a new and important input to the proton size puzzle.