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Germanium Detector Array) Should Get to the Bottom of This Hypothesis

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Germanium Detector Array) Should Get to the Bottom of This Hypothesis Next to photons, neutrinos are the most abundant par- ticles in the universe. Still, they are almost invisible to us since they interact with matter extremely weakly. Their most remarkable feature is currently only Are neutrinos identical to their an assumption and still antiparticles? awaits verification - neu- Are they responsible for the lack trinos could be their own of antimatter in the universe? antiparticles. This property What are their masses? Inflation How did neutrinos influence the would confirm theoretical formation of structures in the preconceptions and would visible universe? significantly change our Through the observation of an current understanding of extremely rare decay process, the structure of matter and the GERDA experiment should of the development of the give answers to these questions. universe. The GERDA experiment (Germanium Detector Array) should get to the bottom of this hypothesis. Big Bang 10-44 Sec. 10-36 Sec. 10-10 Sec. 10-5 Sec. 100 Sec. 400.000 years 1 bill. years 13.7 bill. years The mission Electron Electron Neutrino = A billion million times the Antineutrino age of the universe, an ? unimaginable duration? Nuclear process – according to theory, this (Z, A) (Z+2, A) is at least how long it would take for half a sample of germanium-76 to decay via the so called neutrinoless In neutrinoless double beta double beta decay. How- decay, two neutrons are ever, this process is only converted into two protons possible if neutrinos and and two electrons simultane- ously. Two neutrinos are also their antiparticles are iden- created that cancel each other tical and if they are massive out if they are their own anti- particles. If GERDA can particles. measure some of these Right: Model of the GERDA extremely rare decays, Experiment. physicists could deduce the mass of the neutrinos and provide crucial input for theoretical models. The physics In GERDA, the detectors have two functions: they provide the germanium-76 atoms for the search for neutrinoless double beta decay as well as measuring the energy of these decays. The detectors weigh Germanium serves not only approximately 2 kg and are as the source for neutrinoless the size of a beverage can. double beta decay but also as The detectors are made the detector. of high-purity germanium Right: The clean room used for crystals that are enriched preparing the detectors. with the heavier isotope germanium-76. Occa- sionally a germanium-76 nucleus could decay through neutrinoless double beta decay, leaving behind traces in the detector. The experiment GERDA Germanium Detector Array The GERDA physicists expect less than one neutrinoless double beta decay per year per kilo- gram of detector material. Therefore, they have to shield the experiment very carefully. The experiment Photomultiplier for identifying is constantly bombarded background radiation. with particles from space or from the surrounding rock Right: View into the empty water tank designed to shield that could distort the results the experiment from ambient of the measurement. For radiation. this reason, the germa- nium detectors hang in a six meter high, four meter wide tank filled with cold liquefied argon. To increase shielding even more, this cryo-tank sits in yet another water-filled tank ten meters in diameter by ten meters high. The tank The Gran Sasso National Laboratory of the Italian National Institute for Nuclear Physics (INFN) is the largest underground laboratory for astro-particle physics in the world. It is located under the highest peaks of the Italian Ap- A deep tunnel leads beneath the penines and shielded by an Italian Abruzzo region into the average of 1400 meters of largest underground laboratory rock. The rock absorbs the in the world. radiation from space mak- Right: The kilometer-long ing it possible for physicists tunnel system leads into three to operate very sensitive experimental halls. measuring equipment. In addition to GERDA, about 15 experiments are being conducted in the three underground halls, each of them one hundred meter long. The laboratory Gran Sasso Institute Today, the only way to National Laboratory for Nuclear Research realize large experiments Assergi, Italy Moscow, Russia in physics is through international cooperation. Institute for Theoretical Jagellonian University and Experimental Physics A total of 15 institutions Cracow, Poland Moscow, Russia are participating in the GERDA experiment: Technische Universität Kurchatov Institute Dresden Moscow, Russia Dresden, Germany Imprint Joint Institute Max-Planck-Institut for Nuclear Research für Physik Publisher: Dubna, Russia Munich, Germany GERDA-collaboration c/o Max-Planck-Institute for Physics (Werner-Heisenberg-Institute) Institute for Reference INFN-Padova Press and Public Relations Materials and Measurements Università di Padova Silke Zollinger Geel, Belgium Padova, Italy Föhringer Ring 6 80805 Munich Tel.: +49 89 32354-292 Max-Planck-Institut Eberhard Karls Fax: +49 89 32267-04 für Kernphysik Universität Tübingen E-Mail: [email protected] Heidelberg, Germany Tübingen, Germany GERDA on the web: www.mpi-hd.mpg.de/gerda INFN-Milano Universität Zürich Editor: Università di Milano Bernd Müller, www.bemueller.de Zurich, Switzerland Milan, Italy Design: Vasco Kintzel, www.kintzel.com Photos: INFN-Milano Bicocca NASA, LNGS, MPI für Kernphysik, Excellence Cluster ’Universe’, Università di Milano Bicocca Universität Tübingen Milan, Italy The team GERDA Germanium Detector Array.
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