An improved limit on the neutrinoless double-electron capture of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msup><mml:mrow></mml:mrow><mml:mn>36</mml:mn></mml:msup></mml:math>Ar with GERDA

The GERmanium Detector Array (Gerda) experiment operated enriched high-purity germanium detectors in a liquid argon cryostat, which contains 0.33% of 36Ar, a candidate isotope for the two-neutrino double-electron capture (2νECEC) and therefore for the neutrinoless double-electron capture (0νECEC). If detected, this process would give evidence of lepton number violation and the Majorana nature of neutrinos. In the radiative 0νECEC of 36Ar, a monochromatic photon is emitted with an energy …