Search for resonant enhancement of neutrinoless double-electron capture by high-precision Penning-trap mass spectrometry

Abstract

The search for neutrinoless double-electron capture can be a good alternative to the neutrinoless double-beta-decay experiments in shedding light on such aspects of neutrino physics as the neutrino type, non-conservation of the total lepton charge and magnitude of the effective Majorana neutrino mass. The probability of neutrinoless double-electron capture can be resonantly enhanced by some orders of magnitude. Although the phenomenon of the resonant enhancement was predicted some decades ago, the search for resonantly enhanced neutrinoless double-electron-capture transitions was hampered by a lack of precise experimental values of the atomic mass differences of the transition initial and final states. Only recent progress in high-precision Penning-trap mass spectrometry has finally provided suitable means for a determination of atomic masses with a sufficient precision and thus given rise to the experimental campaign for a search for resonantly enhanced transitions. In this article, after an introduction to the theory of neutrinoless double-electron capture and the Penning-trap technique, a review is given on the results of systematic very precise direct Penning-trap measurements of the atomic mass differences of the nuclides which can undergo double-electron capture. The mass differences of 14 nuclear pairs have already been determined with a typical uncertainty of tens to a few hundreds of eV. Partial or even full resonant enhancement of the neutrinoless double-electron-capture probability has been discovered for 152Gd and 156Dy. In 156Dy a multiple resonance phenomenon has been revealed. For some transitions the half-lives have been estimated (152Gd, 164Er, 180W, 156Dy).

Majorana neutrinos and other Majorana particles: theory and experiment

“…15.3.2 and 15.3.3, see eqs. (62) - (65). Notice that in the standard model there is no Majorana mass term for left-handed neutrinos, i.e.…”

“…The neutrinoless double electron capture may be resonantly enhanced provided that the total energy release is very close to the excitation energy of the A(Z − 2, N + 2) * atomic state. The search for isotopes with suitable atomic mass differences and excitation energies of the daughter atoms is currently under way [65].…”

Search for2βdecays of96Ru and104Ru by ultralow-background HPGeBelli1, Bernabei2, Cappella3 et al. 2013Phys. Rev. C

“…+ , 555.8 keV) ≥ 6.6 × 10 20 yr, As for resonance 0ν2ε capture, intensive high-precision measurements of Q 2β values during last few years (see reviews [52] [53] were set on the level of only T 1/2 > 10 16 yr (this is related with 156 Dy low natural abundance δ = 0.056% [12]). …”

The electron capture in 163Ho experiment – ECHo

“…The determination of the neutrino mass scale is a challenging task due to the smallness of the masses and to the weak interaction with other standard model particles. There exist several approaches which can potentially yield this result: the analysis of the visible structures in the universe [4], the observation of neutrinoless double beta decay [5,6] and resonantly enhanced double electron capture [7], the measurement of the time of flight of neutrinos emitted in supernova explosions [8] and the analysis of the kinematics of low energy beta decays and electron capture (EC) processes [9]. In particular, direct kinematical methods allow to perform a model-independent measurement of the electron neutrino and antineutrino mass with high sensitivity and low systematic uncertainties.…”