Decay energy measurement reveals the potential of 159Dy for neutrino mass determination
The astonishingly light elementary particle, the neutrino, keeps challenging researchers. After postulation of its existence in 1930, fundamental properties of the neutrino have been extensively studied. By now, it is known that they are massive, yet extremely light elementary particles. The exact mass of neutrinos remains as one of the most fundamental open questions in modern physics.
Laboratory experiments that are dedicated for measuring the mass of a neutrino are based on a very simple processes, namely beta decay and electron capture. These emit a neutrino allowing the deduction of its mass. This, however, is an extremely challenging avenue requiring careful analysis of the reaction kinematics. This does not just require a measurement setup that is finely tuned and sensitive to the subtle effect the finite neutrino mass imposes – it is necessary to detect a vast number of these decays.
It is a great advantage for these studies that a decay releases as little energy as possible. This ensures the experiment to be the most sensitive to the neutrino mass. Currently, only few decays are utilized while searches for new candidates are being carried out.
Researchers at the accelerator laboratory of the Department of Physics of the University of ´³²â±¹Ã¤²õ°ì²â±ôä (JYFL) found recently a new candidate for neutrino-mass measurements: Electron capture (EC) in 159Dy atom where an electron is captured from an atomic orbital by the 159Dy nucleus. They conducted a high-precision weighing of the 159Dy atom and its decay product utilizing a Penning trap. The measurement revealed that EC to one particular nuclear state is within a lucrative energy range. This prompted the theory side of the collaboration to pursue state-of-the-art nuclear and atomic calculations to model the expected outcome of the decay. The modeling was done in collaboration with the local JYFL nuclear-theory group and researchers at Kurchatov Institute in Moscow, Russia, and it revealed the EC in 159Dy to be about ten times more sensitive to electron-neutrino mass than the EC in 163Ho, which is currently utilized in neutrino-mass measurements.
This encouraging result paves the way to next-generation neutrino-mass experiments, which can utilize EC in 159Dy and in other potential candidates currently actively searched for at JYFL.
The results were published in Physical Review Letters, .