High-precision Penning trap measures of B-decay Q-Values for neutrino physics

Matthew Redshaw, Central Michigan University (Principal Investigator)

The discovery of neutrino flavor oscillations has shown that neutrinos have non-zero masses. This result has led to modifications of the Standard Model and has wide-ranging implications in fields from particle physics to cosmology. However, important fundamental questions remain: What is the absolute neutrino mass scale? Is the neutrino a Majorana or a Dirac particle? To address these questions, several large-scale neutrino experiments are now underway, and more are being planned. These include both direct neutrino mass measurements and searches for neutrinoless double beta-decay. Planning these experiments and interpreting their results will require accurate determinations of the relevant beta-decay “Q-values.” The Q-value is essentially the mass difference between the initial (parent) and final (daughter) nuclides in the decay. The goal of this research is to provide, using Penning Trap Mass Spectrometry (PTMS), high-precision Q-values for the beta decays of the isotopes under consideration for neutrino experiments. A new PTMS facility will be constructed at Central Michigan University to determine the Q-values of ¹⁸⁷Re and ¹⁶³Ho to a fractional precision of about 10 parts per trillion, which is the accuracy required for direct neutrino mass measurements. In addition, existing PTMS facilities at the National Superconducting Cyclotron Laboratory and Argonne National Laboratory will be used to search for ultra-low Q-values (less than 1 keV) in beta decays of certain initial isotopes to excited-state daughter nuclei. In many a priori possible candidate beta decays, the masses of the parent and daughter nuclides are not yet known with sufficient accuracy to determine whether the decay is actually allowed. If a beta-decay with an ultra-low Q-value is identified, it may prove useful in motivating future direct neutrino mass measurements. We will also carry out PTMS measurements that determine double beta-decay and double-electron-capture Q-values as well as Q-values for other rare weak decays, which may prove useful for other current and future experiments.