Recent experiments at the Gesellschaft für Schwerionenforschung (GSI) in Darmstadt claimed evidence for periodic modulation in the electron capture decay probability of hydrogen-like ions of ¹⁴²Pm and ¹⁴⁰Pr. These surprising observations have prompted suggestions that neutrino mass and neutrino mixing might cause such an effect. Experiments at Berkeley and Munich with electron capture in neutral atoms failed to confirm the GSI findings. I will review the positive and negative experimental evidence for modulation and some of the suggestions for the physics underlying the results. I will also discuss the state of the ongoing theoretical controversy about the compatibility of the neutrino explanation for the GSI effect with the basics principles of quantum mechanics.

Argonne Physics Division Colloquium Schedule