Time-Modulation of Orbital Electron Capture Decays by Mixing of Massive Neutrinos Original Research Article

We report on the observation of time-modulated orbital EC decays of H-like 140Pr58+, 142Pm60+, and 122I52+ (preliminary) ions with only one electron in the K-shell coasting in the ESR storage ring of GSI with a velocity β=0.71 and a spread Δv/v∼5×10−7. The decays were observed with time resolved single ion Schottky Mass Spectroscopy by observation of the time of change of the precisely measured revolution frequency of the mother into the daughter ion which is proportional to the mass change or Q-value of the decay. We observed in the EC-branches exponential decay curves time-modulated with periods View the MathML source and amplitude a=0.18(3) for 140Pr decays, View the MathML source and a=0.23(4) for 142Pm decays, and View the MathML source and a=0.19(3) for 122I decays (preliminary) in the laboratory frame. The simultaneously measured β+ branch of 142Pm shows no modulation with a<0.03. An explanation by mixing of massive electron neutrinos has been suggested, according to which the observed modulation frequency yields a value for the quadratic mass difference: View the MathML source. This value is 2.9 times larger than the value derived by the KamLAND antineutrino oscillation experiment.