$^{159}$Dy electron-capture: a strong new candidate for neutrino mass determination

Z. Ge , T. Eronen , K.S. Tyrin , J. Kotila , J. Kostensalo , D.A. Nesterenko , O. Beliuskina , R. de Groote , A. de Roubin (1) , S. Geldhof , W. Gins , M. Hukkanen (1) , A. Jokinen , A. Kankainen , Á. Koszorús , M.I. Krivoruchenko , S. Kujanpää , I.D. Moore , A. Raggio , S. Rinta-Antila , J. Suhonen , V. Virtanen , A.P. Weaver , A. Zadvornaya

1 CENBG - Centre d'Etudes Nucléaires de Bordeaux Gradignan

The ground state to ground state electron-capture $Q$ value of ${}^{159}\mathrm{Dy}$ ($3/2^{-}$) has been measured directly using the double Penning trap mass spectrometer JYFLTRAP. A value of 364.73(19) keV was obtained from a measurement of the cyclotron frequency ratio of the decay parent ${}^{159}\mathrm{Dy}$ and the decay daughter ${}^{159}\mathrm{Tb}$ ions using the novel phase-imaging ion-cyclotron resonance technique. The $Q$ values for allowed Gamow-Teller transition to $5/2^{-}$ and the third-forbidden unique transition to $11/2^{+}$ state with excitation energies of 363.5449(14) keV and 362.050(40) keV in ${}^{159}\mathrm{Tb}$ were determined to be 1.18(19) keV and 2.68(19) keV, respectively. The high-precision $Q$ value of transition $3/2^{-}\to 5/2^{-}$ from this work, revealing itself as the lowest electron-capture $Q$ value, is used to unambiguously characterize all the possible lines that are present in its electron-capture spectrum. We performed atomic many-body calculations for both transitions to determine electron-capture probabilities from various atomic orbitals and found an order of magnitude enhancement in the event rates near the end point of energy spectrum in the transition to the $5/2^{-}$ nuclear excited state, which can become very interesting once the experimental challenges of identifying decays into excited states are overcome. The transition to the $11/2^{+}$ state is strongly suppressed and found unsuitable for measuring the neutrino mass. These results show that the electron-capture in the ${}^{159}\mathrm{Dy}$ atom, going to the $5/2^{-}$ state of the ${}^{159}\mathrm{Tb}$ nucleus, is a new candidate that may open the way to determine the electron-neutrino mass in the sub-eV region by studying electron-capture. Further experimental feasibility studies, including coincidence measurements with realistic detectors, will be of great interest.

Mots clés: neutrino: mass; electron: capture; mass: scale; energy: decay; dysprosium; Penning trap; semileptonic decay; sensitivity; experimental results

Domaines: Physique Nucléaire Expérimentale [nucl-ex]

Z. Ge, T. Eronen, K.S. Tyrin, J. Kotila, J. Kostensalo, et al.. $^{159}$Dy electron-capture: a strong new candidate for neutrino mass determination. Phys.Rev.Lett., 2021, 127 (27), pp.272301. ⟨10.1103/PhysRevLett.127.272301⟩. ⟨hal-03271133⟩