An improved limit on the neutrinoless double-electron capture of $$^{36}$$Ar with GERDA

• Published in: The European physical journal. C, Particles and fields Particles and fields, 2024-01, Vol.84 (1), Article 34
• Main Authors: Agostini, M, Alexander, A, Araujo, G. R, Bakalyarov, A. M, Balata, M, Barabanov, I, Baudis, L
• Format: Article
• Language: English
• Subjects: Detectors; Electrons
• ISSN: 1434-6052; 1434-6044; 1434-6052
• DOI: 10.1140/epjc/s10052-023-12280-6

The GERmanium Detector Array ( Gerda ) experiment operated enriched high-purity germanium detectors in a liquid argon cryostat, which contains 0.33% of $$^{36}$$ 36 Ar, a candidate isotope for the two-neutrino double-electron capture (2 $$\nu $$ ν ECEC) and therefore for the neutrinoless double-electron capture (0 $$\nu $$ ν ECEC). If detected, this process would give evidence of lepton number violation and the Majorana nature of neutrinos. In the radiative 0 $$\nu $$ ν ECEC of $$^{36}$$ 36 Ar, a monochromatic photon is emitted with an energy of 429.88 keV, which may be detected by the Gerda germanium detectors. We searched for the $$^{36}$$ 36 Ar 0 $$\nu $$ ν ECEC with Gerda data, with a total live time of 4.34 year (3.08 year accumulated during Gerda Phase II and 1.26 year during Gerda Phase I). No signal was found and a 90% CL lower limit on the half-life of this process was established $$T_{1/2} >1.5\cdot 10^{22} $$ T 1 / 2 > 1.5 · 10 22  year.