Alpha-event characterization for germanium detectors

A detailed study of alpha interactions on the passivated surface of a germanium detector is presented. Germanium detectors can be used to search for both neutrinoless double beta decay of 76Ge and direct interaction of dark matter. In order to increase the sensitivity to both neutrinoless double beta decay and dark matter beyond the current state of the art, the next generation of germanium-based experiments has to have a mass of about one ton and has to reduce the background by a factor of ten. The choices of detector technology facilitating both searches and the background reduction are one of the biggest challenges for such an experiment. Surface contaminations on the material close to the detectors or on the detectors themselves, can generate a background due to alpha particles, which was found to be limiting in some experiments. The characterization of events induced by alpha particles will help to identify such events and thus eliminate them as sources of background. An especially designed segmented true-coaxial detector was probed with alpha particles from an 241Am source inside the test-stand GALATEA, located at the MPI f¨ur Physik in Munich. Pulse shape analysis was performed to identify the characteristics of alpha events. The properties of the detector directly underneath the passivation layer on the end-plate were also studied. As part of the detector characterization, the thickness of the effective dead layer was determined. The studies presented here suggest improvements on detector design, which would allow an effective reduction of alpha background in next generation of germanium-based experiments.Eine detaillierte Studie alpha-induzierter Ereignisse auf der passivierten Oberfläche eines Germaniumdetektors wird präsentiert. Germanium Detektoren werden sowohl bei der Suche nach neutrinolosem Doppelbetazerfall von 76Ge als auch bei der Suche nach Dunkler Materie eingesetzt. Um die Sensitivität über das in den heutigen Experimenten erreichte hinaus zu verbessern, ist es nötig die aktive Masse der Experimente um eine Größenordnung auf eine Tonne zu steigern und gleichzeitig den Untergrund um eine Größenordnung zu reduzieren. Die Auswahl der Detektoroptionen, um beide Suchen zu ermöglichen und den Untergrund zu reduzieren, ist eine der großen Herausforderungen für solch ein Experiment. Oberflächenkontaminationen auf Materialien in der nahe Umgebung der Detektoren oder auf den Detektoren selber führen oft zu Untergründen, die in einigen Fällen die Sensitivität von Experimenten begrenzt haben. Die Charakterisierung von alpha-induzierten Ereignissen birgt die Möglichkeit, sie im Experiment als solche zu erkennen und sie auf diese Weise als Untergrund zu eliminieren. Ein speziell für solche Studien konzipierter segmentierter vollständig koaxialer Detektor wurde im GALATEA Teststand des MPI für Physik in München mit Hilfe einer 241Am Quelle untersucht. Zur Charakterisierung der alpha-induzierten Ereignisse wurden Pulsformanalysen durchgeführt. Die Eigenschaften des Detektors im Volumen direkt unter der passivierten Endplatte wurden ebenfalls untersucht. Ein Teil dieser Untersuchung war die Bestimmung der effektiven Totzone des Detektors. Die hier vorgelegten Studien suggerieren, dass gewisse Veränderungen im Detektordesign zur Verbesserung der Identifikation von alpha-induzierten Ereignissen in germaniumbasierten Experimenten führen würden

Future Opportunities with Germanium Detectors at the China Jinping Underground Laboratories

The China Jinping underground Laboratory (CJPL) is the deepest underground laboratory in operation in the world. The extremely low muon flux makes CJPL a good candidate to host low background experiments looking for rare events like neutrino-less double-beta decays ($0\nu\beta\beta$ decay) or dark matter (DM) interactions. Feasibility and R&D studies are performed to combine these two searches in a common 'One-Ton-Germanium facility' to be built in a low-background environment such as CJPL

Neutron Shielding Simulations and Muon-induced Neutrons

Cosmic-ray neutrons and muons can produce background in low-rate experiments due to the production of long-lived radioisotopes during transport above ground. This kind of background can be reduced by shielding the detector components during transport. Cosmic-ray neutron and muon ($\mu^{+}$ and $\mu^{-}$) shielding simulations with the GEANT4 based framework MaGe were done to estimate the shielding properties of water, plastic, soil, steel, concrete, copper, LNGS rock and lead. The shielding power of cosmic-ray neutrons and muon-induced neutrons as well as the total neutron fluxes at different shielding depths are presented. Also the neutron backscattering effect was investigated and was found to be significant

Latest results from the PolarquEEEst missions

The PolarquEEEst scientific programme consists in a series of measurements of the cosmic ray flux up to the highest latitudes, well beyond the Polar Article Circle. It started in Summer 2018, when one telescope for cosmic rays was installed on a sailboat leaving from North Iceland, to circumnavigate the Svalbard archipelago and land in Tromsø. It collected data up to 82N, measuring with unprecedented precision the charged particle rate at sea level in these regions. During Fall of the same year and Spring 2019 the PolarquEEEst programme continued with a series of measurements performed using the same detector, which took place first in Italy, with the southernmost point reached at Lampedusa, and then in Germany, with the goal to measure the dependence of cosmic charged particle rate with latitude. Then, in May 2019, the PolarquEEEst collaboration accomplished another important result, installing a cosmic ray observatory for the detection of secondary cosmic muons at Ny Alesund, at 79N, made of three independent identical detectors positioned a few hundred meters from each other, and synchronized in order to operate together as a network. This configuration allows high precision measurements never performed before at these latitudes on a long term, also interesting for their connection with environmental phenomena. Here the various missions will be presented, and the latest results from the measurements performed will be shown

Search for Multi-Coincidence Cosmic Ray Events over Large Distances with the EEE MRPC Telescopes

The existence of independent, yet time correlated, Extensive Air Showers (EAS) has been discussed over the past years, with emphasis on possible physical mechanisms that could justify their observation. The detector network of the Extreme Energy Events (EEE) Collaboration, with its approximately 60 cosmic ray telescopes deployed over the Italian territory, has the potential to search for such events, employing different analysis strategies. In this paper, we have analyzed a set of EEE data, corresponding to an approximately five month observation period, searching for multi-coincidence events among several far telescopes, within a time window of 1 ms. Events with up to 12 coincident telescopes have been observed. Results were compared to expectations from a random distribution of events and discussed with reference to the relativistic dust grain hypothesis

Towards a full and realistic simulation framework for the Extreme Energy Events experiment

The network of MRPC (Multi-gap Resistive Plate Chambers) telescopes of the Extreme Energy Events experiment (EEE) was designed to study very high energy cosmic rays through detection of secondary cosmic muons in the hadronic shower. To better understand and predict the behavior of such events, a GEANT4-based simulation framework that well reproduces the response of individual telescopes was built. Simulations are crucial to better understand the detectors performance in current setup and how these are affected by the specific installations. This is the first step towards a full simulation framework that includes a realistic generation, now limited to muons, of secondary particles and propagation through the atmosphere of the shower produced by primary rays. The current framework can be used to characterize and optimize the array of EEE telescopes, simulating not only the single detectors but also telescope's clusters, providing insight in extreme energy and rare events. In this contribution, the EEE simulation framework and future plans will be presented

Looking for long-range correlations among the EEE telescopes

none60siThe search for long-range correlations among air showers is one of the main goal of the Extreme Energy Events (EEE) Project. The existence of such events has only been supposed theoretically through several physical mechanisms, the most convincing being the so-called GZ effect, based on the photodisintegration of a heavy primary nucleus in the solar field. Even with a large detector coverage, current rate expectations are of few events per year. To measure time correlations among distant air showers, sparse arrays of detection stations spread over large areas are needed. A very limited number of experimental setups can perform this measurement and few experimental results have been reported over the past years. Started in 2004 the EEE project is a network of about 60 cosmic muons tracking telescopes made by 3 wide area Multigap Resistive Plate Chambers (MRPCs), sensitive to the direction of incident charged cosmic particles. The telescopes are distributed over the whole Italian territory, thus making the EEE array an ideal tool for the detection of long-range time correlations among extensive air showers. In this paper we will describe the analysis strategies adopted to search for such rare correlation events, together with the results obtained analysing the full statistics collected by the EEE telescopes.restrictedLa Rocca, P.; Abbrescia, Marcello; Avanzini, Carlo; Baldini, Luca; Baldini Ferroli, Rinaldo; Batignani, Giovanni; Battaglieri, Marco; Boi, Stefano; Bossini, Edoardo; Carnesecchi, Francesca; Cicalo, Corrado; Cifarelli, Luisa; Coccetti, Fabrizio; Coccia, Eugenio; Corvaglia, Alessandro; De Gruttola, Daniele; De Pasquale, Salvatore; Fabbri, Franco L.; Galante, Lorenzo; Garbini, Marco; Gemme, Gianluca; Gnesi, Ivan; Grazzi, Stefano; Hatzifotiadou, Despina; Liu, Zheng; Mandaglio, Giuseppe; Maron, Gaetano; Mazziotta, Mario Nicola; Mulliri, Alice; Nania, Rosario; Noferini, Francesco; Nozzoli, Francesco; Palmonari, Federico; Panareo, Marco; Panetta, Maria Paola; Paoletti, Riccardo; Pellegrino, Carmelo; Pinazza, Ombretta; Pinto, Chiara; Pisano, Silvia; Riggi, Francesco; Righini, Giancarlo Cesare; Ripoli, Cristina; Rizzi, Matteo; Sartorelli, Gabriella; Scapparone, Eugenio; Schioppa, Marco; Scribano, Angelo; Selvi, Marco; Serri, Gabriella; Squarcia, Sandro; Taiuti, Mauro; Terreni, Giuseppe; Trifirò, Antonio; Trimarchi, Marina; Vistoli, Cristina; Votano, Lucia; Williams, Crispin; Zichichi, Antonino; Zuyeuski, RomanLa Rocca, P.; Abbrescia, Marcello; Avanzini, Carlo; Baldini, Luca; Baldini Ferroli, Rinaldo; Batignani, Giovanni; Battaglieri, Marco; Boi, Stefano; Bossini, Edoardo; Carnesecchi, Francesca; Cicalo, Corrado; Cifarelli, Luisa; Coccetti, Fabrizio; Coccia, Eugenio; Corvaglia, Alessandro; De Gruttola, Daniele; De Pasquale, Salvatore; Fabbri, Franco L.; Galante, Lorenzo; Garbini, Marco; Gemme, Gianluca; Gnesi, Ivan; Grazzi, Stefano; Hatzifotiadou, Despina; Liu, Zheng; Mandaglio, Giuseppe; Maron, Gaetano; Mazziotta, Mario Nicola; Mulliri, Alice; Nania, Rosario; Noferini, Francesco; Nozzoli, Francesco; Palmonari, Federico; Panareo, Marco; Panetta, Maria Paola; Paoletti, Riccardo; Pellegrino, Carmelo; Pinazza, Ombretta; Pinto, Chiara; Pisano, Silvia; Riggi, Francesco; Righini, Giancarlo Cesare; Ripoli, Cristina; Rizzi, Matteo; Sartorelli, Gabriella; Scapparone, Eugenio; Schioppa, Marco; Scribano, Angelo; Selvi, Marco; Serri, Gabriella; Squarcia, Sandro; Taiuti, Mauro; Terreni, Giuseppe; Trifirò, Antonio; Trimarchi, Marina; Vistoli, Cristina; Votano, Lucia; Williams, Crispin; Zichichi, Antonino; Zuyeuski, Roma