First results of GERDA Phase II and consistency with background models

The GERDA (GERmanium Detector Array) is an experiment for the search of neutrinoless double beta decay (0νββ) in (76)Ge, located at Laboratori Nazionali del Gran Sasso of INFN (Italy). GERDA operates bare high purity germanium detectors submersed in liquid Argon (LAr). Phase II of data-taking started in Dec 2015 and is currently ongoing. In Phase II 35 kg of germanium detectors enriched in (76)Ge including thirty newly produced Broad Energy Germanium (BEGe) detectors is operating to reach an exposure of 100 kg·yr within about 3 years data taking. The design goal of Phase II is to reduce the background by one order of magnitude to get the sensitivity for $T_{1/2}^{0\nu } = O\left( {{{10}^{26}}} \right){\rm{ yr}}$. To achieve the necessary background reduction, the setup was complemented with LAr veto. Analysis of the background spectrum of Phase II demonstrates consistency with the background models. Furthermore (226)Ra and (232)Th contamination levels consistent with screening results. In the first Phase II data release we found no hint for a 0νββ decay signal and place a limit of this process $T_{1/2}^{0\nu } > 5.3 \cdot {10^{25}}$ yr (90% C.L., sensitivity 4.0·10(25) yr). First results of GERDA Phase II will be presented

First results of GERDA Phase II

The GErmanium Detector Array (Gerda) experiment, located at the Laboratori Nazionali del Gran Sass15, searches for the 0νββ decay of 76Ge. Gerda Phase II was started in December 2015, aiming to reach a sensitivity on the 0νββ decay half-life larger than 1026 yr in three yr of data taking with about 100 kg·yr exposure with background index of about 10-3 cts/(keV·kg·yr). The major upgrade of Phase II is the deployment of thirty newly produced Broad Energy Germanium detectors. They contribute to the background reduction with better energy resolution and enhanced pulse shape discrimination. To achieve the necessary background reduction, the setup was complemented with LAr veto. After 6 months of operation a first data release with 10.8 kg·yr exposure was performed, showing that the background goal has been achieved. A new lower limit on the 0νββ decay half life of 76Ge of 5.3·1025 yr (90% C.L.) has been set

Study of the GERDA Phase II background spectrum

The Gerda experiment, located at the Laboratori Nazionali del Gran Sasso (LNGS) of INFN in Italy, searches for the neutrinoless double beta (0νββ) decay of (76)Ge. Gerda Phase II is aiming to reach a sensitivity for the 0νββ half life of 10(26) yr in ∼ 3 years of physics data taking with 100 kg·yr of exposure and a background index of ∼ 10(−)(3) cts/(keV·kg·yr). After 6 months of acquisition a first data release with 10.8 kg·yr of exposure is performed, showing that the design background is achieved. In this work a study of the Phase II background spectrum, the main spectral structures and the background sources will be presented and discussed

Active background suppression with the liquid argon scintillation veto of GERDA Phase II

The observation of neutrinoless double beta decay would allow to shed light onto the particle nature of neutrinos. Gerda is aiming to perform a background-free search for this process using high purity germanium detectors enriched in (76)Ge operated in liquid argon. This goal relies on the application of active background suppression techniques. A low background light instrumentation has been installed for Phase II to detect events with coincident energy deposition in the nearby liquid argon. The intended background index of ∼10(−)(3) cts/(keV·ky·yr) has been confirmed