First search for 2$\varepsilon$ and $\varepsilonβ^+$ processes in $^{168}$Yb

P. Belli; R. Bernabei; R. S. Boiko; F. Cappella; V. Caracciolo; R. Cerulli; F. A. Danevich; M. L. di Vacri; A. Incicchitti; B. N. Kropivyansky; M. Laubenstein; S. Nisi; D. V. Poda; O. G. Polischuk; V. I. Tretyak

doi:10.1016/j.nuclphysa.2019.07.003

arXiv · 1906.10915

First search for 2$\varepsilon$ and $\varepsilonβ^+$ processes in $^{168}$Yb

P. Belli·R. Bernabei·R. S. Boiko·F. Cappella·V. Caracciolo·R. Cerulli·F. A. Danevich·M. L. di Vacri·A. Incicchitti·B. N. Kropivyansky·M. Laubenstein·S. Nisi·D. V. Poda·O. G. Polischuk·V. I. Tretyak

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Abstract

The double-electron capture and the electron capture with positron emission in $^{168}$Yb have been investigated for the first time at the STELLA facility of the Gran Sasso underground laboratory (Italy) measuring 371 g of highly purified ytterbium oxide placed on the end-cap of a 465 cm$^3$ ultra-low-background high purity Germanium detector (HPGe). No gamma associated to double beta processes in $^{168}$Yb have been observed after 2074 h of data taking. This has allowed setting the half-life limits on the level of $\lim T_{1/2}\sim$ $10^{14}-10^{18}$ yr at 90\% C.L. Particularly, a lower half-life limit on a possible resonant neutrinoless double-electron capture in $^{168}$Yb to the $(2)^-$ 1403.7 keV excited state of $^{168}$Er is set as $T_{1/2}\geq1.9\times 10^{18}$ yr at 90\% C.L. Half-life limits $T_{1/2}^{2ν(0ν)}\geq 4.5(4.3)\times10^{16}$ yr were set on the $2ν(0ν)2β^-$ decay of $^{176}$Yb to the $2^+$ 84.3 keV first excited level of $^{176}$Hf.

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P. Belli, R. Bernabei, R. S. Boiko, F. Cappella, V. Caracciolo, R. Cerulli, F. A. Danevich, M. L. di Vacri, A. Incicchitti, B. N. Kropivyansky, M. Laubenstein, S. Nisi, D. V. Poda, O. G. Polischuk, V. I. Tretyak. 2019-06-26. First search for 2$\varepsilon$ and $\varepsilonβ^+$ processes in $^{168}$Yb. https://doi.org/10.1016/j.nuclphysa.2019.07.003

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