Stefan Ulmer

Stefan Ulmer is a chief scientist at RIKEN, a Professor at Duesseldorf, and Founder/ Spokesperson of CERN’s BASE collaboration. He has received his PhD degree (2011) for the “first observation of spin flips with a single trapped proton”. In 2012 he was appointed as a PI at RIKEN to compare the fundamental properties of protons and antiprotons with highest precision. In 2014 his team compared the proton/antiproton charge/mass ratio with a fractional precision of 69 parts in a trillion (p.p.t.), which was later (2022) improved to 16 p.p.t. precision. 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.