Precise Penning trap Q value determinations for forbidden and low energy β-decays*

Historically, nuclear β-decay studies have provided insight into the nature of the weak interaction. They continue to be relevant for tests of the standard model, searches for new physics, and investigations of the properties of neutrinos. The β-decay Q value, the energy equivalent of the mass difference between parent and daughter atoms, can be precisely measured using Penning trap mass spectrometry to provide a result that is completely independent from spectroscopy measurements that determine the kinetic energy of the decay products. Q value measurements can be used as an inputs for theoretical calculations of β-spectrum shape factors, electron branching ratios, and half-lives. They also provide a test of systematics in precise β-spectroscopy measurements, and enable the identification of β-decays with very low Q values that could be used in direct neutrino mass determination experiments. In this presentation we will review Q value measurements for the forbidden decays of long-lived primordial nuclides, including a recent Penning trap measurement of ¹⁷⁶Lu. We will also discuss a recent evaluation of all potential ultra-low Q value decay nuclides and present recent results from a measurement on ⁷⁵Se.