First search for 2ε and εβ+ processes in 168Yb

The double-electron capture and the electron capture with positron emission in Yb-168 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 Yb-168 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 similar to 10(14)-10(18) yr at 90% C.L. Particularly, a lower half-life limit on a possible resonant neutrinoless double-electron capture in Yb-168 to the (2)(-) 1403.7 keV excited state of Er-168 is set as T-1/2 >= 1.9 x 10(18) yr at 90% C.L. Half-life limits T-1/2(2 nu(0 nu)) >= 4.5(4.3) x 10(16) yr were set on the 2 nu(0 nu)2 beta(-) decay of Yb-176 to the 2(+) 84.3 keV first excited level of Hf-176. (C) 2019 Elsevier B.V. All rights reserved.