Leader: Prof. Dr. Randolf Pohl
Our research is dedicated to laser spectroscopy of muonic atoms and ions. These are exotic systems in which one negative muon replaces the atoms' electrons. Muons are very the heavy brothers of electrons. Both are point-like particles, but muons are about 200 times heavier. Therefore, muons get on average 200 times closer to the atomic nucleus than electrons do.This makes the muon much more sensitive to the properties of the nucleus. Charge and magnetic radius of the nucleus, for example, change the excitation spectrum of muonic atoms and ions considerably. Thus we can obtain accurate knowledge about the properties of the lightest nuclei by doing laser spectroscopy of these muonic systems.
We have so far determined both the charge and magnetic radius of the proton from laser spectroscopy of muonic hydrogen. Our charge radius is ten times more precise than any previous measurement, but there is a striking 4% discrepancy. This so-called ‘proton radius puzzle’ has attracted a lot of interest.
At present we are investigating muonic deuterium, and from fall 2013 on we will also have a look at muonic helium. We are going to measure the charge radii of 3He and 4He ten times more precisely than before and hope to shed new light on the proton radius puzzle. Within the framework of a large international collaboration we are responsible for parts of thelasers and the muon beam, as well as the data acquisition and analysis. The experiments are being carried out at the Paul-Scherrer-Institut (PSI) in Villigen (Switzerland) which offers the world's strongest muon beams. Our work receives generous funding from the European Research Council through the ERC Starting Grant “Charge Radius Experiment with Muonic Atoms” (CREMA).