Feasibility study of the observation of the neutrino accompanied double beta-decay of Ge-76 to the 0+(1) excited state of Se-76 using segmented germanium detectors

Neutrino accompanied double beta-decay of Ge-76 can populate the ground state and the excited states of Se-76. While the decay to the ground state has been observed with a half-life of 1.74 +0.18 -0.16 10^21 years, decays to the excited states have not yet been observed. Nuclear matrix elements depend on details of the nuclear transitions. A measurement of the half-life of the transition considered here could help to reduce the uncertainties of the calculations of the nuclear matrix element for the neutrinoless double beta decay of Ge-76. This parameter relates the half-life of the process to the effective Majorana neutrino mass. The results of a feasibility study to detect the neutrino accompanied double beta-decay of Ge-76 to the excited states of Se-76 are presented in this paper. Segmented germanium detectors were assumed in this study. Such detectors, enriched in Ge-76 to a level of about 86%, will be deployed in the GERDA experiment located at the INFN Gran Sasso National Laboratory, Italy. It is shown that the decay of Ge-76 to the 1122 keV 0+ level of Se-76 can be observed in GERDA provided that the half-life of the process is in the range favoured by the present calculations which is 7.5 10^21 y to 3.1 10^23 y.Comment: 18 pages, 4 figures. Submitted to Nucl. Phys.

Virtual depth by active background suppression: Revisiting the cosmic muon induced background of GERDA Phase II

In-situ production of long-lived isotopes by cosmic muon interactions may generate a non-negligible background for deep underground rare event searches. Previous Monte Carlo studies for the GERDA experiment at LNGS identified the delayed decays of $^{77}$Ge and its metastable state $^{77m}$Ge as dominant cosmogenic background in the search for neutrinoless double beta decay of $^{76}$Ge. This might limit the sensitivity of next generation experiments aiming for increased $^{76}$Ge mass at background-free conditions and thereby define a minimum depth requirement. A re-evaluation of the $^{77(m)}$Ge background for the GERDA experiment has been carried out by a set of Monte Carlo simulations. The obtained $^{77(m)}$Ge production rate is (0.21$\pm$0.01) nuclei/(kg$\cdot$yr). After application of state-of-the-art active background suppression techniques and simple delayed coincidence cuts this corresponds to a background contribution of (2.7$\pm$0.3)$\cdot10^{-6}$ cts/(keV$\cdot$kg$\cdot$yr). The suppression achieved by this strategy equals an effective muon flux reduction of more than one order of magnitude. This virtual depth increase opens the way for next generation rare event searches.Comment: 9 pages, 5 figure

Off-line data quality monitoring for the GERDA experiment

GERDA is an experiment searching for the neutrinoless {\beta}{\beta} decay of Ge-76. The experiment uses an array of high-purity germanium detectors, enriched in Ge-76, directly immersed in liquid argon. GERDA recently started the physics data taking using eight enriched coaxial detectors. The status of the experiment has to be closely monitored in order to promptly identify possible instabilities or problems. The on-line slow control system is complemented by a regular off-line monitoring of data quality. This ensures that data are qualified to be used in the physics analysis and allows to reject data sets which do not meet the minimum quality standards. The off-line data monitoring is entirely performed within the software framework GELATIO. In addition, a relational database, complemented by a web-based interface, was developed to support the off-line monitoring and to automatically provide information to daily assess data quality. The concept and the performance of the off-line monitoring tools were tested and validated during the one-year commissioning phase.Comment: Contribution prepared for the proceeding of the TAUP 2011 conferenc

Overview of the European Underground Facilities

Deep underground laboratories are the only places where the extremely low background radiation level required for most experiments looking for rare events in physics and astroparticle physics can be achieved. Underground sites are also the most suitable location for very low background gamma-ray spectrometers, able to assay trace radioactive contaminants. Many operational infrastructures are already available worldwide for science, differing for depth, dimension and rock characteristics. Other underground sites are emerging as potential new laboratories. In this paper the European underground sites are reviewed, giving a particular emphasis on their relative strength and complementarity. A coordination and integration effort among the European Union underground infrastructures was initiated by the EU-funded ILIAS project and proved to be very effective.Comment: Prepared for the Proceedings of the Topical Workshop in Low Radioactivity Techniques (Sudbury, Canada), August 28-29, 2010m (LRT2010). To be published on AIP conference proceeding

Monte Carlo evaluation of the external gamma, neutron and muon induced background sources in the CUORE experiment

CUORE is a 1 ton scale cryogenic experiment aiming at the measurement of the Majorana mass of the electron neutrino. The detector is an array of 988 TeO2 bolometers used for a calorimetric detection of the two electrons emitted in the BB0n of 130Te. The sensitivity of the experiment to the lowest Majorana mass is determined by the rate of background events that can mimic a BB0n. In this paper we investigate the contribution of external sources i.e. environmental gammas, neutrons and cosmic ray muons to the CUORE background and show that the shielding setup designed for CUORE guarantees a reduction of this external background down to a level <1.0E-02 c/keV/kg/y at the Q-value, as required by the physical goal of the experiment.Comment: 14 pages, 7 figure

Observation of beta decay of In-115 to the first excited level of Sn-115

In the context of the LENS R&D solar neutrino project, the gamma spectrum of a sample of metallic indium was measured using a single experimental setup of 4 HP-Ge detectors located underground at the Gran Sasso National Laboratories (LNGS), Italy. A gamma line at the energy (497.48 +/- 0.21) keV was found that is not present in the background spectrum and that can be identified as a gamma quantum following the beta decay of In-115 to the first excited state of Sn-115 (9/2+ --> 3/2+). This decay channel of In-115, which is reported here for the first time, has an extremely low Q-value, Q = (2 +/- 4) keV, and has a much lower probability than the well-known ground state-ground state transition, being the branching ratio b = (1.18 +/- 0.31) 10^-6. This could be the beta decay with the lowest known Q-value. The limit on charge non-conserving beta decay of In-115 is set at 90% C.L. as tau > 4.1 10^20 y.Comment: 19 pages, 5 figures, 2 table

Demonstration and Comparison of Operation of Photomultiplier Tubes at Liquid Argon Temperature

Liquified noble gases are widely used as a target in direct Dark Matter searches. Signals from scintillation in the liquid, following energy deposition from the recoil nuclei scattered by Dark Matter particles (e.g. WIMPs), should be recorded down to very low energies by photosensors suitably designed to operate at cryogenic temperatures. Liquid Argon based detectors for Dark Matter searches currently implement photo multiplier tubes for signal read-out. In the last few years PMTs with photocathodes operating down to liquid Argon temperatures (87 K) have been specially developed with increasing Quantum Efficiency characteristics. The most recent of these, Hamamatsu Photonics Mod. R11065 with peak QE up to about 35%, has been extensively tested within the R&D program of the WArP Collaboration. During these testes the Hamamatsu PMTs showed superb performance and allowed obtaining a light yield around 7 phel/keVee in a Liquid Argon detector with a photocathodic coverage in the 12% range, sufficient for detection of events down to few keVee of energy deposition. This shows that this new type of PMT is suited for experimental applications, in particular for new direct Dark Matter searches with LAr-based experiments

Beta decay of 115-In to the first excited level of 115-Sn: Potential outcome for neutrino mass

Recent observation of beta decay of 115-In to the first excited level of 115-Sn with an extremely low Q_beta value (Q_beta ~ 1 keV) could be used to set a limit on neutrino mass. To give restriction potentially competitive with those extracted from experiments with 3-H (~2 eV) and 187-Re (~15 eV), atomic mass difference between 115-In and 115-Sn and energy of the first 115-Sn level should be remeasured with higher accuracy (possibly of the order of ~1 eV).Comment: 9 pages, 3 figures; talk at the NANP'05 Conferenc

The MGDO software library for data analysis in Ge neutrinoless double-beta decay experiments

The GERDA and Majorana experiments will search for neutrinoless double-beta decay of germanium-76 using isotopically enriched high-purity germanium detectors. Although the experiments differ in conceptual design, they share many aspects in common, and in particular will employ similar data analysis techniques. The collaborations are jointly developing a C++ software library, MGDO, which contains a set of data objects and interfaces to encapsulate, store and manage physical quantities of interest, such as waveforms and high-purity germanium detector geometries. These data objects define a common format for persistent data, whether it is generated by Monte Carlo simulations or an experimental apparatus, to reduce code duplication and to ease the exchange of information between detector systems. MGDO also includes general-purpose analysis tools that can be used for the processing of measured or simulated digital signals. The MGDO design is based on the Object-Oriented programming paradigm and is very flexible, allowing for easy extension and customization of the components. The tools provided by the MGDO libraries are used by both GERDA and Majorana.Comment: 4 pages, 1 figure, proceedings for TAUP201

The BNO-LNGS joint measurement of the solar neutrino capture rate in 71Ga

We describe a cooperative measurement of the capture rate of solar neutrinos by the reaction 71Ga(\nu_e,e^-)71Ge. Extractions were made from a portion of the gallium target in the Russian-American Gallium Experiment SAGE and the extraction samples were transported to the Gran Sasso laboratory for synthesis and counting at the Gallium Neutrino Observatory GNO. Six extractions of this type were made and the resultant solar neutrino capture rate was 64 ^{+24}_{-22} SNU, which agrees well with the overall result of the gallium experiments. The major purpose of this experiment was to make it possible for SAGE to continue their regular schedule of monthly solar neutrino extractions without interruption while a separate experiment was underway to measure the response of 71Ga to neutrinos from an 37Ar source. As side benefits, this experiment proved the feasibility of long-distance sample transport in ultralow background radiochemical experiments and familiarized each group with the methods and techniques of the other.Comment: 7 pages, no figures; minor additions in version