High-precision Q-value measurement confirms the potential of 135Cs for antineutrino-mass detection
Abstract
The ground-state-to-ground-state β-decay Q-value of 135Cs(7/2+)\,135Ba(3/2+) was directly measured for the first time utilizing the Phase-Imaging Ion-Cyclotron Resonance (PI-ICR) technique at the JYFLTRAP Penning-trap setup. It is the first direct determination of this Q-value and its value of 268.66(30)\,keV is a factor of three more precise than the currently adopted Q-value in the Atomic Mass Evaluation 2016. Moreover, the Q-value deduced from the β-decay endpoint energy has been found to deviate from our result by approximately 6 standard deviations. The measurement confirms that the first-forbidden unique β--decay transition 135Cs(7/2+)\,135Ba(11/2-) is a candidate for antineutrino-mass measurements with an ultra-low Q-value of 0.44(31) keV. This Q-value is almost an order of magnitude smaller than in any presently running or planned direct (anti)neutrino-mass experiment.