Cm3 detector neutrino science: search for neutrino oscillations in electron capture decay

Paul Vetter


A recent publication from a group at GSI (arXiv:nucl-ex/0801.2079) claimed to observe time oscillation of the decay rate of electron capture isotopes.  They attributed this effect to neutrino species mixing which caused a superposition of neutrino mass states to contribute to the decay rate.  A model, expanded in other arXiv papers argued that the different neutrino mass states produce interference in the calculation of the decay rate for the two-body electron capture decay.  The well-measured oscillation frequency was calculated to be proportional to the neutrino mass difference squared, $\Delta m_{12}2$.  If correct, this interpretation could revolutionize the study of neutrino mixing.  A small flurry of arXiv papers debated the issue in terms of quantum measurement theory.  An eclectic group performed an experiment at the LBNL 88" Cyclotron using the Berkeley Gas-filled Separator to attempt to confirm the neutrino oscillation result.  While our approach was much less complex than the GSI measurement, we would easily have observed the oscillating decay rate of electron capture decays if the neutrino oscillation interpretation were correct.
I will try to summarize the GSI results, the interpretation in terms of neutrino oscillations, the controversy over quantum mechanics, and our experiment -- which did not find an oscillating decay rate.