Time-reversal breaking in isospin-hindered ⁴⁷K β decay

Isospin-hindered Fermi transitions in β decay enhance sensitivity to time-reversal violation (TRV) effects in the progeny nucleus [Barroso and Blin-Stoyle [Phys Lett 45B 178 (1973)]. A key figure of merit is the ratio of the TRV matrix element to the Coulomb interaction's isospin-breaking matrix element (rather than strong interaction matrix elements), potentially enhancing sensitivity by orders of magnitude. We will show progress towards the isospin-hindered Fermi/Gamow-Teller 81% decay branch of ⁴⁷K, for which measurements of the TRV correlation D I ^. v_β X v_ν are possible using TRIUMF's Neutral Atom Trap for β decay (TRINAT). A γ-β-tensor alignment correlation using polarized RIB and modern segmented spectrometers has similar TRV sensitivity. We will first measure the isospin breaking using the asymmetry of emission of the nuclear progeny with respect to the initial spin, which vanishes for pure G-T decay [J.R.A. Pitcairn et al. Phys Rev C 79 015501 (2009)] and is linear in the isospin breaking Fermi matrix element. Compact high photopeak efficiency, high resolution GAGG scintillators may enable resolving final states to measure the isospin breaking with TRINAT.