Dzhelepov Laboratory of Nuclear Problems

Date and Time: Wednesday, 23 September 2020, at 11:00 AM

Venue: Online conference in Zoom

Seminar topic: “Search for “standard” and “non-standard” modes of the ββ-decay and other rare processes in GERDA, LEGEND and elsewhere”

Speaker: A. A. Smolnikov

Abstract:

The neutrinoless double beta decay 0νββ in revealing neutrino properties and New Physics beyond the Standard Model. The main goal of the GERDA (GERmanium Detector Array) experiment is searching for the 0νββ-decay of ⁷⁶Ge. By operating bare germanium detectors, enriched in ⁷⁶Ge, in an active liquid argon shield, GERDA achieved an unprecedently low background index of 5•10^-4 counts/(keV•kg•yr) in the signal region. No signal is observed after 127.2 kg•yr of total exposure, and a limit on the half-life of 0νββ-decay in ⁷⁶Ge is set at T_1/2 > 1,8•10²⁶ yr.

The data taking with 200 kg of ⁷⁶Ge is planned to be launched in 2021. Despite the fact that searching for the 0νββ-decay of ⁷⁶Ge to the ground state of the daughter nucleus ⁷⁶Se is currently the main and the most ambitious goal of GERDA and LEGEND, a wide range of other ββ-modes and mechanisms, as well as a number of other rare processes, were, are being and will be investigated within GERDA and LEGEND, providing many new important results.

A brief overview will be devoted to both the results for the “standard” and “non-standard” modes of the ββ decay, already obtained at the first stages of GERDA, and the expected results for all accumulated statistics in GERDA Phase-II, as well as to the planned sensitivity for all modes at the stages LEGEND-200 and LEGEND-1000. Within this seminar, the “non-standard” modes and mechanisms of the ββ-decay include the two-neutrino and neutrinoless ββ-decay of ⁷⁶Ge to excited states of ⁷⁶Se, the double beta decay with emission of majorons 0νββ_χ, the 2νββ-decay with a bosonic neutrino admixture, the decay with Lorentz invariance violation 2νββLV and a number of others proposed in various theoretical models. Beside the investigation of the ββ-decay of ⁷⁶Ge, a significant improvement in the ³⁶Ar half-life limit for the double electron capture 0νECEC is expected as a result of a complete analysis of the GERDA Phase-II data. The results of the search for the Tri-nucleon decay and new results recently published by the GERDA collaboration on the search for hypothetical particles, Super-WIMPs, will also be presented. In conclusion, some general aspects of the strategy for setting up and carrying out the planned double beta decay experiments will be discussed.

(In connection with elections for the position of a senior researcher)

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