Stefan Ulmer is a chief scientist at RIKEN, a Professor at Düsseldorf, and Founder/ Spokesperson of CERN’s BASE collaboration. Using newly invented Penning trap methods, BASE also reported on the most precise measurement of the antiproton magnetic moment with a fractional precision of 1.5 p.p.b. Together with an 11-fold improved proton magnetic moment measurement performed at BASE-Mainz, this measurement improved the previous best direct baryon moment CPT test by a factor of >3000, also setting most stringent limits on antimatter/axion coupling.

The striking imbalance of matter over antimatter in our universe has yet to be understood. Plugging the best physics theories together, the big bang model and the standard model of particle physics, we would expect a matter/antimatter ratio of 1, and a radiative universe. Observations and theory differ by almost nine orders of magnitude. To contribute to solving this puzzle, Stefan Ulmer and his team are comparing the properties of protons and antiprotons with highest precision. This tests the standard model, which assumes that matter/antimatter pairs have exactly symmetric properties. Any measured difference would hint at new physics and possibly contribute to an explanation why our matter-dominated universe actually exists. In their experiments they use Penning traps to compare protons and antiprotons with highest precision. Dr. Ulmer and his team have compared proton/antiproton charge-to-mass ratios with a fractional accuracy of 16 parts in a trillion. In addition, they have developed and established new multi-Penning trap techniques – reservoir traps and elegant two particle protocols – to measure proton/antiproton magnetic moments with fractional accuracies of 0.3 p.p.b. and 1.5 p.p.b., respectively. This improved the previous best proton/antiproton moment CPT test by >3000 times. They have also used their antimatter systems as probes for dark matter, and have recently established sympathetic cooling of a single trapped proton by coupling the particle to laser cooled beryllium ions.

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