Investigation of double beta decay of $^{58}$Ni with the Obelix spectrometer

International audienceInvestigation of double beta decay processes (β+EC, EC/EC) of 58Ni was performed at the Modane underground laboratory (LSM, France, 4800 m w.e.) using ultra low-background HPGe detector Obelix with sensitive volume of 600 cm3 and a sample of natural nickel, containing ∼68% of 58Ni with a mass of ∼21.7 kg. New experimental limits on 2νβ+EC decay of 58Ni to the ground 0+ and 21+, 811 keV excited state of 58Fe, and 2νEC/EC decay of 58Ni to 21+, 811 keV and 22+ 1 675 keV excited states of 58Fe were obtained from the preliminary calculation of experimental data accumulated in ∼88d. They are - T1/2(β+ EC, 0+ → 0+) > 1.4 ×1021 y; T1/2(β+EC,0+→21+)>1.7×1022 y, T1/2(EC/EC, 0+→21+)>2.4×1022 y, T1/2(EC/EC, 0+→22+)>2.1×1022 y. For resonant neutrino-less radiative EC/EC decay with energy of 1 918.3 keV a new experimental limit of T1/2 (0νEC/EC − res, 1918keV) > 4.7 ×1022 y was also obtained. All limits are at 90 % CL