First direct search for $2\epsilon$ and $\epsilon\beta^+$ decay of $^{144}$Sm and $2\beta^-$ decay of $^{154}$Sm

• Published in: The European physical journal. A, Hadrons and nuclei Hadrons and nuclei, 2019, Vol.55 (11)
• Main Authors: Belli, P., Bernabei, R., Boiko, R.S., Cappella, F., Caracciolo, V., Cerulli, R., Danevich, F.A., Di Marco, A., Incicchitti, A., Kropivyansky, B.N., Laubenstein, M., Nisi, S., Poda, D.V., Polischuk, O.G., Tretyak, V.I.
• Format: Article
• Language: English
• Subjects: Nuclear Experiment; Physics
• ISSN: 1434-6001; 1434-601X
• DOI: 10.1140/epja/i2019-12911-3

The first direct search for the double electron capture ($ 2\epsilon$) and the electron capture with positron emission ($ \epsilon\beta^+$) in$^{144}$Sm to the ground state and to the excited levels of$^{144}$Nd was realized by measuring --over 1899h-- a 342g sample of highly purified samarium oxide (Sm$_{2}$O$_{3}$) with the ultra-low background HP-Ge $\gamma$ spectrometer GeCris (465cm$^{3}$) at the STELLA facility of the Gran Sasso National Laboratory (LNGS). No effect was observed and half-life limits were estimated at the level of $ T_{1/2} \sim (0.1 - 1.3) \times 10^{20}$ yr (90% C.L.). Moreover, for the first time half-life limits of the double beta ($ 2\beta^-$) decay of$^{154}$Sm to several excited levels of$^{154}$Gd have been set, they are at the level of $ T_{1/2} \sim (0.06 - 8) \times 10^{20}$ yr (90% C.L.).