First direct search for 2EC, ECbeta+ decay of 144Sm and 2beta- decay of 154Sm

The first direct search for the double electron capture (2EC) and the electron capture with positron emission (ECβ+) in 144Sm to the ground state and to the excited levels of 144Nd was realized by measuring — over 1899 h — a 342 g sample of highly purified samarium oxide (Sm2O3) with the ultra-low background HP-Ge γ spectrometer GeCris (465 cm^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 T1/2 ∼ (0.1–1.3)×10^20 yr (90% C.L.). Moreover, for the first time half-life limits of the double beta (2β−) decay of 154Sm to several excited levels of 154Gd have been set; they are at the level of T1/2 ∼ (0.06–8) × 10^20 yr (90% C.L.).