Geneva, 19 October 2017.

Today, the BASE collaboration has published in Nature a new measurement of the magnetic moment of the antiproton, with a precision exceeding that of the proton. Thanks to a new method involving simultaneous measurements made on two separately trapped antiprotons in two Penning traps, BASE has succeeded in breaking its own record, published in January. This new result improves the precision of the previous measurement by a factor of 350 and allows researchers to compare matter and antimatter with unprecedented accuracy.

“This result is the culmination of many years of continuous research and development and the successful
completion of one of the most difficult measurements ever performed in a Penning trap instrument,” said BASE Spokesperson Stefan Ulmer.

The results are consistent with the magnetic moments of the proton and antiproton being equal,
and the experimental uncertainty of the new antiproton measurement is now significantly smaller
than that of the equivalent measurement for protons. The magnetic moment of the antiproton has
been found to be 2.792 847 344 1(42), while the magnetic moment of the proton was found to be
2.792 847 350(9) by the same collaboration of researchers in 2014 at BASE’s companion experiment
in Mainz, Germany.

“It is probably the first time that physicists have achieved a more precise measurement for baryonic
antimatter than for matter, which demonstrates the extraordinary progress accomplished at CERN’s
Antiproton Decelerator,” added first author of the study Christian Smorra.