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Erratum: Production and validation of scintillating structural components from low-background Poly(ethylene naphthalate)
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Background free search for neutrinoless double beta decay with GERDA Phase II
The Standard Model of particle physics cannot explain the dominance of matter
over anti-matter in our Universe. In many model extensions this is a very
natural consequence of neutrinos being their own anti-particles (Majorana
particles) which implies that a lepton number violating radioactive decay named
neutrinoless double beta () decay should exist. The detection
of this extremely rare hypothetical process requires utmost suppression of any
kind of backgrounds.
The GERDA collaboration searches for decay of Ge
(^{76}\rm{Ge} \rightarrow\,^{76}\rm{Se} + 2e^-) by operating bare detectors
made from germanium with enriched Ge fraction in liquid argon. Here, we
report on first data of GERDA Phase II. A background level of
cts/(keVkgyr) has been achieved which is the world-best if
weighted by the narrow energy-signal region of germanium detectors. Combining
Phase I and II data we find no signal and deduce a new lower limit for the
half-life of yr at 90 % C.L. Our sensitivity of
yr is competitive with the one of experiments with
significantly larger isotope mass.
GERDA is the first experiment that will be background-free
up to its design exposure. This progress relies on a novel active veto system,
the superior germanium detector energy resolution and the improved background
recognition of our new detectors. The unique discovery potential of an
essentially background-free search for decay motivates a
larger germanium experiment with higher sensitivity.Comment: 14 pages, 9 figures, 1 table; ; data, figures and images available at
http://www.mpi-hd.mpg/gerda/publi
Search for Neutrinoless Double-Beta Decay of Te with CUORE-0
We report the results of a search for neutrinoless double-beta decay in a
9.8~kgyr exposure of Te using a bolometric detector array,
CUORE-0. The characteristic detector energy resolution and background level in
the region of interest are FWHM and ~counts/(keVkgyr), respectively. The
median 90%~C.L. lower-limit sensitivity of the experiment is and surpasses the sensitivity of previous searches. We find
no evidence for neutrinoless double-beta decay of Te and place a
Bayesian lower bound on the decay half-life, ~ at 90%~C.L. Combining CUORE-0 data with the 19.75~kgyr
exposure of Te from the Cuoricino experiment we obtain at 90%~C.L.~(Bayesian), the most stringent
limit to date on this half-life. Using a range of nuclear matrix element
estimates we interpret this as a limit on the effective Majorana neutrino mass,
-- .Comment: 6 pages, 5 figures, updated version as published in PR
Results from the CUORE-0 experiment
The CUORE-0 experiment searched for neutrinoless double beta decay in 130Te using an array of 52 tellurium dioxide crystals, operated as bolometers at a temperature of 10 mK. It took data in the Gran Sasso National Laboratory (Italy) since March 2013 to March 2015. We present the results of a search for neutrinoless double beta decay in 9.8 kg-years 130Te exposure that allowed us to set the most stringent limit to date on this half-life. The performance of the detector in terms of background and energy resolution is also reported
CUORE and CUORE-0 experiments
Neutrino oscillation experiments proved that neutrinos have mass and this enhanced the interest in neutrinoless double-beta decay (0vßß). The observation of this very rare hypothetical decay would prove the leptonic number violation and would give us indications about neutrinos mass hierarchy and absolute mass scale. CUORE (Cryogenic Underground Observatory for Rare Events) is an array of 988 crystals of TeO2, for a total sensitive mass of 741 kg. Its goal is the observation of 0vßß of 130Te. The crystals, placed into the a dilution cryostat, are operated as bolometers at a temperature close to 10 mK. CUORE commissioning phase has been concluded recently in Gran Sasso National Laboratory, Italy, and data taking is expected to start in spring 2017. If target background rate is reached (0.01counts/day/keV/kg), the sensibility of CUORE will be, in five years of data taking, T1/21026years (1? CL). In order to test the quality of materials and optimize the construction procedures, the collaboration realized CUORE-0, that took data from spring of 2013 to summer 2015. Here, after a brief description of CUORE, I report its commissioning status and CUORE-0 results
Performance of novel VUV-sensitive Silicon Photo-Multipliers for nEXO
Liquid xenon time projection chambers are promising detectors to search for
neutrinoless double beta decay (0), due to their response
uniformity, monolithic sensitive volume, scalability to large target masses,
and suitability for extremely low background operations. The nEXO collaboration
has designed a tonne-scale time projection chamber that aims to search for
0 of \ce{^{136}Xe} with projected half-life sensitivity of
~yr. To reach this sensitivity, the design goal for nEXO is
1\% energy resolution at the decay -value (~keV).
Reaching this resolution requires the efficient collection of both the
ionization and scintillation produced in the detector. The nEXO design employs
Silicon Photo-Multipliers (SiPMs) to detect the vacuum ultra-violet, 175 nm
scintillation light of liquid xenon. This paper reports on the characterization
of the newest vacuum ultra-violet sensitive Fondazione Bruno Kessler VUVHD3
SiPMs specifically designed for nEXO, as well as new measurements on new test
samples of previously characterised Hamamatsu VUV4 Multi Pixel Photon Counters
(MPPCs). Various SiPM and MPPC parameters, such as dark noise, gain, direct
crosstalk, correlated avalanches and photon detection efficiency were measured
as a function of the applied over voltage and wavelength at liquid xenon
temperature (163~K). The results from this study are used to provide updated
estimates of the achievable energy resolution at the decay -value for the
nEXO design
Production and validation of scintillating structural components from low-background Poly(ethylene naphthalate)
Poly Ethylene Naphthalate (PEN) is an industrial polymer plastic which is investigated as a low background, transparent, scintillating and wavelength shifting structural material. PEN scintillates in the blue region and has excellent mechanical properties both at room and cryogenic temperatures. Thus, it is an ideal candidate for active structural components in experiments for the search of rare events like neutrinoless double-beta decay or dark matter recoils. Such optically active structures improve the identification and rejection efficiency of backgrounds events, like this improving the sensitivity of experiments. This paper reports on the production of radiopure and transparent PEN plates These structures can be used to mount germanium detectors operating in cryogenic liquids (LAr, LN). Thus, as first application PEN holders will be used to mount the Ge detectors in the Legend-200 experiment. The whole process from cleaning the raw material to testing the PEN active components under final operational conditions is reported