Speaker
Description
Search for the Majorana Nature of Neutrino with the LEGEND Experiment
A. Biondi on behalf of the LEGEND Collaboration
Observation of the neutrinoless double beta (0$\nu\beta\beta$) decay would establish that neutrinos are Majorana particles and demonstrate violation of lepton number, providing a key ingredient for understanding the origin of neutrino masses and the matter-antimatter asymmetry in the Universe. As one of the most sensitive probes of physics beyond the Standard Model, the search for the $0\nu\beta\beta$ decay plays a central role in modern neutrino physics.
The Large Enriched Germanium Experiment for Neutrinoless $\beta\beta$ Decay (LEGEND) is a phased program devoted to search for the $0\nu\beta\beta$ decay in the $^{76}$Ge isotope using enriched high-purity germanium detectors operated in a low-background environment. The first phase, LEGEND-200, is taking data at the Laboratori Nazionali del Gran Sasso (LNGS) since March 2023. Following the latest upgrade, the experiment is operating 138 kg of enriched detectors, and it will employ up to 200 kg of $^{enr}$Ge in its final design. LEGEND-200 has reported its first physics results based on 61 $kg \cdot yr$ of exposure, demonstrating excellent energy resolution and very low background levels. From the collective analysis of data from GERDA, MAJORANA DEMONSTRATOR and LEGEND-200, the LEGEND Collaboration has set one of the best limits in the field on the half-life of $0\nu\beta\beta$ decay, namely $T^{0\nu}_{1/2} > 1.9 \times 10^{26}~yr$ at the 90% confidence level. It corresponds to a limit on the effective Majorana mass of $m_{\beta\beta} < 70 - 200$ meV, depending from the chosen nuclear matrix element.
The next phase, LEGEND-1000, will scale the detector mass to 1000 kg of enriched germanium while further reducing the background by an order of magnitude. With an exposure of about 10 $t\cdot yr$, it is expected to operate in a quasi background-free regime and reach a discovery sensitivity for half-lives beyond $10^{28}~yr$, covering the inverted neutrino mass ordering region.
In this talk I will provide an overview of the LEGEND program, present the latest results from LEGEND-200, and discuss the design and projected sensitivity of LEGEND-1000.