Today a paper was published in Phys. Rev. Lett.in which a collaboration of researchers from Max Planck Institute for Nuclear Physics, Heidelberg, Germany and Members of BASE/RIKEN's Ulmer Fundamental Symmetries Lab report on a three-fold improved measurement of the proton mass in natural units. The resulting value 1.007 276 466 583(15)(29) u is three times more precise than the presently recommended value, however it is significantly smaller than the current CODATA standard value. Measurements by other authors yielded discrepancies with respect to the mass of the tritium atom, the heaviest hydrogen isotope (T = 3H), and the mass of light helium (3He) compared to the “semiheavy” hydrogen molecule HD (D = 2H, deuterium, heavy hydrogen). Our result contributes to solving this puzzle, since it corrects the proton’s mass in the proper direction.

The experiment has been developed by a group of young physicists around Sven Sturm and Klaus Blaum from MPI-K, Andreas Mooser and Stefan Ulmer from BASE/RIKEN FSL developed parts for the ultra-sensitive single particle detectors which are used in this experiment.