Welcome to AG Pohl

Welcome to the laser spectroscopy group of Prof. Dr. Randolf Pohl.

We focus on laser spectroscopy of light hydrogen-like muonic atoms and ions and the precise determination of their nuclear charge and magnetic radii.
A muonic atom/ion is a bound state of a negative muon and a bare nucleus, where the muon is the heavy cousin of an electron. Its large mass - it is 200 times heavier than an electron - causes the muon to be 200 times closer to the nucleus compared to an electron. This leads to an highly enhanced sensitivity to nuclear properties as e.g. the "size" of a nucleus, i.e. the electric or magnetic charge radius.

Up to now we have measured the size of the charge and of the magnetization distribution of the proton. The charge radius we determined from laser spectroscopy in muonic hydrogen is 10 times more precise than all previous determinations, but at the same time 4% smaller than the previous values. This discrepancy is known as the Proton Radius Puzzle and became Nature title story in 2010.
Our more recent determination of the deuteron charge radius also results to be smaller and so confirmed the discrepancy of the proton charge radius. This measurement has been published in Science.

Our future measurements will contribute to a better understanding of the lightest nuclei and push the limits of the determinations of fundamental parameters, as e.g. the Rydberg constant or the nuclear charge radii. This work furthermore leads to improved tests of bound state QED and nuclear model theories.