## The Quest for Majorana Neutrinos with GERDA and LEGEND *Note unusual time*

#### by Prof. Stefan Schonert

##### at Particles and Fields Seminar

Mon, 05 Sep 2022, 16:30
Sacta-Rashi Building for Physics (54), room 207

#### Abstract

Since neutrinos have no electric charges, they may be their own antiparticles, referred to as Majorana neutrinos, and thus violate lepton number conservation. Neutrinoless double beta decay would be a direct consequence, and the search for this decay mode is the most sensitive method to unravel the Majorana nature of neutrinos. By operating bare germanium diodes, enriched in Ge-76, in an active liquid argon shield, GERDA achieved an unprecedently low background index of $5.2 \times 10^{−4}$~counts/keV kg yr in the signal region and superseeded the design goal to collect an exposure of 100 kg yr in a background-free regime. When combined with the result of Phase I, no signal is observed after 127.2 kg yr of total exposure. A limit on the half-life of 0νββ decay in Ge-76 is set at $T_1/2 > 1.8 \times 10^{26}$~yr at 90\% C.L. [1], which coincides with the sensitivity assuming no signal. Majorana neutrino masses are therefore constrained to $m_{\beta\beta} < 79–180$~meV at 90\% C.L.. The new LEGEND Collaboration was founded in 2016 to develop a phased, Ge-76-based double-beta decay experimental program with discovery potential a half-life beyond $10^{28}$ years, using existing resources as appropriate to expedite physics results. Its first stage, LEGEND-200, is currently under commissioning, re-purposing the GERDA experimental infrastructures at LNGS, Italy, and is scheduled to go into commissioning in 2021. In parallel, we are preparing the design for the ton-scale LEGEND-1000 stage of the experiment. In this talk, I will present the final results of GERDA and discuss the preparatory works and plans for LEGEND [2].

[1] Final Results of GERDA on the Search for Neutrinoless Double-β Decay, https://journals.aps.org/prl/pdf/10.1103/PhysRevLett.125.252502
[2] LEGEND-1000 Preconceptual Design Report arXiv:2107.11462

Created on 30-08-2022 by Citron, Zvi (zhcitron)
Updaded on 30-08-2022 by Citron, Zvi (zhcitron)