Franz Kottmann

Date

27 May 2015

Host

Klaus Kirch

Title

Proton radius puzzle and Lamb shift in muonic hydrogen

Abstract

Muonic hydrogen, a proton orbited by a negative muon, is one of the most basic atomic systems. A few years ago, we have measured the Lamb shift in muonic hydrogen (energy difference between 2S and 2P states) with infrared laser spectroscopy in a pioneering experiment at the Paul Scherrer Institute (PSI). Combined with QED calculations we determined the proton radius (root-mean-square charge radius). Our value is 4% smaller and deviates significantly from the previous values from electron-proton scattering and hydrogen spectroscopy. This discrepancy in a basic field of particle physics created a lot of theoretical investigations and initiated new experiments, but the “proton radius puzzle” is still unsolved today. I will give an overview about the present status, including new data from muonic deuterium and helium.