First results of the CUORICINO experiment
S. PirroC. ArnaboldiD. R. ArtusaF. T. AvignoneM. BalataI. BandacM. BarucciJ. W. BeemanC. BrofferioC. BucciS. CapelliFrancesco CapozziL. CarboneS. CebriánO. CremonesiR. J. CreswickA. de WaardHorácio A. FarachA. FascillaE. FioriniG. FrossatiA. GiulianiP. GorlaE. E. HallerI.G. IrastorzaR. McDonaldA. MoralesE. B. NormanA. NucciottiE. OlivieriV. PalmieriEdoardo PascaM. PavanM. PedrettiG. PessinaE. PrevitaliC. PobesM. PyleL. RisegariC. RosenfeldM. SistiA. R. SmithL. TorresG. Ventura
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The MAJORANA Collaboration is constructing the MAJORANA DEMONSTRATOR, an ultra-low background, modular, HPGe detector array with a mass of 44.8-kg (29.7 kg enriched >88% in Ge-76) to search for neutrinoless double beta decay in Ge-76. The next generation of tonnescale Ge-based neutrinoless double beta decay searches will probe the neutrino mass scale in the inverted-hierarchy region. The MAJORANA DEMONSTRATOR is envisioned to demonstrate a path forward to achieve a background rate at or below 1 count/tonne/year in the 4 keV region of interest around the Q-value of 2039 keV. The MAJORANA DEMONSTRATOR follows a modular implementation to be easily scalable to the next generation experiment. First data taken with the DEMONSTRATOR are introduced here.
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After more than 3/4 of century from its proposal, Neutrinoless Double Beta Decay (NLDBD) is still missing observation and continues to represent the only practical method for investigating the Dirac/Majorana nature of neutrinos. In case neutrinos would be Majorana particles, NLDBD would provide unique informations on their properties (absolute mass scale and Majorana phases). Boosted by the discovery of neutrino oscillations, a number of experiments with improved sensitivity have been proposed in the past decade. Some of them have recently started operation and others are ready to start. They will push the experimental sensitivity on the decay halflife beyond 1026 year, starting to analyze the region of the inverted mass hierarchy. The status and perspectives of the ongoing experimental effort are reviewed. Uncertainties coming from the calculation othe decay nuclear matrix elements (NME) as well as the recently suggested possibility of a relevant quenching of the axial coupling constant are also discussed.
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Neutrinoless double-beta decay is a hypothesized process where in some even-even nuclei it might be possible for two neutrons to simultaneously decay into two protons and two electrons without emitting neutrinos. This is possible only if neutrinos are Majorana particles, i.e. fermions that are their own antiparticles. Neutrinos being Majorana particles would explicitly violate lepton number conservation, and might play a role in the matter-antimatter asymmetry in the universe. The observation of neutrinoless double-beta decay would also provide complementary information related to neutrino masses. The Majorana Collaboration is constructing the Majorana Demonstrator, a 40-kg modular germanium detector array, to search for the Neutrinoless double-beta decay of 76Ge and to demonstrate a background rate at or below 3 counts/(ROI-t-y) in the 4 keV region of interest (ROI) around the 2039 keV Q-value for 76Ge Neutrinoless double-beta decay. In this paper, we discuss the physics of neutrinoless double beta decay and then focus on the Majorana Demonstrator, including its design and approach to achieve ultra-low backgrounds and the status of the experiment.
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The observation of neutrinoless double-beta decay would resolve the Majorana nature of the neutrino and could provide information on the absolute scale of the neutrino mass. The initial phase of the Majorana experiment, known as the Demonstrator, will house 40 kg of Ge in an ultra-low background shielded environment at the 4850' level of the Sanford Underground Laboratory in Lead, SD. The objective of the Demonstrator is to determine whether a future 1-tonne experiment can achieve a background goal of one count per tonne-year in a narrow region of interest around the 76Ge neutrinoless double-beta decay peak.
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Neutrinoless double beta decay (0νββ) is the only experiment that could probe the Majorana nature of the neutrino. Here we study the theoretical implications of 0νββ for models yielding tri-bimaximal lepton mixing like A4 and S4.
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The MAJORANA Collaboration is constructing the MAJORANA DEMONSTRATOR, an ultra-low background, modular, HPGe detector array with a mass of 44.8-kg (29.7 kg enriched ≥88% in 76Ge) to search for neutrinoless double beta decay in 76Ge. The next generation of tonnescale Ge-based neutrinoless double beta decay searches will probe the neutrino mass scale in the inverted-hierarchy region. The MAJORANA DEMONSTRATOR is envisioned to demonstratepath forward to achieve a background rate at or below 1 count/tonne/year in the 4 keV region of interest around the Q-value of 2039 keV. The MAJORANA DEMONSTRATOR follows a modular implementation to be easily scalable to the next generation experiment. First data taken with the DEMONSTRATOR are introduced here.
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The search for neutrinoless double beta decay is the only practical way to test whether neutrinos are Majorana or Dirac particles. The next generation of experiments aim to probe the effective Majorana neutrino mass down to few 10 meV, as predicted by oscillation experiments in case of the inverse mass hierarchy. According to recent nuclear matrix calculations, the predicted decay rates per mass of double beta isotope are varying within a factor of few when comparing them within the same theoretical model framework. The sensitivity of the upcoming experiments depend therefore primarily on the available mass of double beta isotopes and the experimental conditions. In particular, the achievable background suppression and the detection efficiency will be decisive for their success.
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Bolometers are ideal devices in the search for neutrinoless Double Beta Decay (0ν DBD). Enlarging the mass of individual detectors would simplify the construction of a large experiment, but would also decrease the background per unit mass induced by α-emitters located close to the surfaces and background arising from external and internal γ's. We present the very promising results obtained with a 2.13 kg TeO2 crystal. This bolometer, cooled down to a temperature of 10.5 mK in a dilution refrigerator located deep underground in the Gran Sasso National Laboratories, represents the largest thermal detector ever operated. The detector exhibited an energy resolution spanning a range from 3.9 keV (at 145 keV) to 7.8 keV (at the 2615 γ-line of 208Tl) FWHM. We discuss the decrease in the background per unit mass that can be achieved increasing the mass of a bolometer.
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