arXiv subjects

G. Piperno

Publications and source records attributed to G. Piperno.

At least 37 records · Page 2Linked to original sources

arXiv2015

The CUORE and CUORE-0 Experiments at Gran Sasso

The Cryogenic Underground Observatory for Rare Events (CUORE) is an experiment to search for neutrinoless double beta decay ($0νββ$) in $^{130}$Te and other rare processes. CUORE is a cryogenic detector composed of 988 TeO$_2$ bolometers for a total mass of about 741 kg. The detector is being constructed at the Laboratori Nazionali del Gran Sasso, Italy, where it will start taking data in 2015. If the target background of 0.01 counts/(keV$\cdot$kg$\cdot$y) will be reached, in five years of data taking CUORE will have an half life sensitivity around $1\times 10^{26}$ y at 90\% C.L. As a first step towards CUORE a smaller experiment CUORE-0, constructed to test and demonstrate the performances expected for CUORE, has been assembled and is running. The detector is a single tower of 52 CUORE-like bolometers that started taking data in spring 2013. The status and perspectives of CUORE will be discussed, and the first CUORE-0 data will be presented.

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arXiv2015

Searching for neutrinoless double-beta decay of $^{130}$Te with CUORE

Neutrinoless double-beta ($0νββ$) decay is a hypothesized lepton-number-violating process that offers the only known means of asserting the possible Majorana nature of neutrino mass. The Cryogenic Underground Observatory for Rare Events (CUORE) is an upcoming experiment designed to search for $0νββ$ decay of $^{130}$Te using an array of 988 TeO$_2$ crystal bolometers operated at 10 mK. The detector will contain 206 kg of $^{130}$Te and have an average energy resolution of 5 keV; the projected $0νββ$ decay half-life sensitivity after five years of live time is $1.6\times 10^{26}$ y at $1σ$ ($9.5\times10^{25}$ y at the 90% confidence level), which corresponds to an upper limit on the effective Majorana mass in the range 40--100 meV (50--130 meV). In this paper we review the experimental techniques used in CUORE as well as its current status and anticipated physics reach.

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arXiv2015

Status of the CUORE and results from the CUORE-0 neutrinoless double beta decay experiments

CUORE is a 741 kg array of TeO2 bolometers for the search of neutrinoless double beta decay of 130Te. The detector is being constructed at the Laboratori Nazionali del Gran Sasso, Italy, where it will start taking data in 2015. If the target background of 0.01 counts/keV/kg/y will be reached, in five years of data taking CUORE will have a 1 sigma half life sensitivity of 10E26 y. CUORE-0 is a smaller experiment constructed to test and demonstrate the performances expected for CUORE. The detector is a single tower of 52 CUORE-like bolometers that started taking data in spring 2013. The status and perspectives of CUORE will be discussed, and the first CUORE-0 data will be presented.

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arXiv2015

CUORE-0 results and prospects for the CUORE experiment

With 741 kg of TeO2 crystals and an excellent energy resolution of 5 keV (0.2%) at the region of interest, the CUORE (Cryogenic Underground Observatory for Rare Events) experiment aims at searching for neutrinoless double beta decay of 130Te with unprecedented sensitivity. Expected to start data taking in 2015, CUORE is currently in an advanced construction phase at LNGS. CUORE projected neutrinoless double beta decay half-life sensitivity is 1.6E26 y at 1 sigma (9.5E25 y at the 90% confidence level), in five years of live time, corresponding to an upper limit on the effective Majorana mass in the range 40-100 meV (50-130 meV). Further background rejection with auxiliary bolometric detectors could improve CUORE sensitivity and competitiveness of bolometric detectors towards a full analysis of the inverted neutrino mass hierarchy. CUORE-0 was built to test and demonstrate the performance of the upcoming CUORE experiment. It consists of a single CUORE tower (52 TeO2 bolometers of 750 g each, arranged in a 13 floor structure) constructed strictly following CUORE recipes both for materials and assembly procedures. An experiment its own, CUORE-0 is expected to reach a sensitivity to the neutrinoless double beta decay half-life of 130Te around 3E24 y in one year of live time. We present an update of the data, corresponding to an exposure of 18.1 kg y. An analysis of the background indicates that the CUORE performance goal is satisfied while the sensitivity goal is within reach.

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arXiv2014

TeO$_2$ bolometers with Cherenkov signal tagging: towards next-generation neutrinoless double beta decay experiments

CUORE, an array of 988 TeO$_2$ bolometers, is about to be one of the most sensitive experiments searching for neutrinoless double-beta decay. Its sensitivity could be further improved by removing the background from $α$ radioactivity. A few years ago it has been pointed out that the signal from $β$s can be tagged by detecting the emitted Cherenkov light, which is not produced by $α$s. In this paper we confirm this possibility. For the first time we measured the Cherenkov light emitted by a CUORE crystal, and found it to be 100 eV at the $Q$-value of the decay. To completely reject the $α$ background, we compute that one needs light detectors with baseline noise below 20 eV RMS, a value which is 3-4 times smaller than the average noise of the bolometric light detectors we are using. We point out that an improved light detector technology must be developed to obtain TeO$_2$ bolometric experiments able to probe the inverted hierarchy of neutrino masses.

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arXiv2014

Measurements and optimization of the light yield of a TeO$_2$ crystal

Bolometers have proven to be good instruments to search for rare processes because of their excellent energy resolution and their extremely low intrinsic background. In this kind of detectors, the capability of discriminating alpha particles from electrons represents an important aspect for the background reduction. One possibility for obtaining such a discrimination is provided by the detection of the Cherenkov light which, at the low energies of the natural radioactivity, is only emitted by electrons. This paper describes the method developed to evaluate the amount of light produced by a crystal of TeO$_2$ when hit by a 511 keV photon. The experimental measurements and the results of a detailed simulation of the crystal and the readout system are shown and compared. A light yield of about 52 Cherenkov photons per deposited MeV was measured. The effect of wrapping the crystal with a PTFE layer, with the aim of maximizing the light collection, is also presented.

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arXiv2014

Initial performance of the CUORE-0 experiment

CUORE-0 is a cryogenic detector that uses an array of tellurium dioxide bolometers to search for neutrinoless double-beta decay of ^{130}Te. We present the first data analysis with 7.1 kg y of total TeO_2 exposure focusing on background measurements and energy resolution. The background rates in the neutrinoless double-beta decay region of interest (2.47 to 2.57 MeV) and in the α background-dominated region (2.70 to 3.90 MeV) have been measured to be 0.071 \pm 0.011 and 0.019 \pm 0.002 counts/keV/kg/y, respectively. The latter result represents a factor of 6 improvement from a predecessor experiment, Cuoricino. The results verify our understanding of the background sources in CUORE-0, which is the basis of extrapolations to the full CUORE detector. The obtained energy resolution (full width at half maximum) in the region of interest is 5.7 keV. Based on the measured background rate and energy resolution in the region of interest, CUORE-0 half-life sensitivity is expected to surpass the observed lower bound of Cuoricino with one year of live time.

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arXiv2014

CUORE and beyond: bolometric techniques to explore inverted neutrino mass hierarchy

The CUORE (Cryogenic Underground Observatory for Rare Events) experiment will search for neutrinoless double beta decay of $^{130}$Te. With 741 kg of TeO$_2$ crystals and an excellent energy resolution of 5 keV (0.2%) at the region of interest, CUORE will be one of the most competitive neutrinoless double beta decay experiments on the horizon. With five years of live time, CUORE projected neutrinoless double beta decay half-life sensitivity is $1.6\times 10^{26}$ y at $1σ$ ($9.5\times10^{25}$ y at the 90% confidence level), which corresponds to an upper limit on the effective Majorana mass in the range 40--100 meV (50--130 meV). Further background rejection with auxiliary light detector can significantly improve the search sensitivity and competitiveness of bolometric detectors to fully explore the inverted neutrino mass hierarchy with $^{130}$Te and possibly other double beta decay candidate nuclei.

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arXiv2014

First bolometric measurement of the two neutrino double beta decay of $^{100}$Mo with a ZnMoO$_4$ crystals array

The large statistics collected during the operation of a ZnMoO$_4$ array, for a total exposure of 1.3 kg $\cdot$ day of $^{100}$Mo, allowed the first bolometric observation of the two neutrino double beta decay of $^{100}$Mo. The observed spectrum of each crystal was reconstructed taking into account the different background contributions due to environmental radioactivity and internal contamination. The analysis of coincidences between the crystals allowed the assignment of constraints to the intensity of the different background sources, resulting in a reconstruction of the measured spectrum down to an energy of $\sim$300 keV. The half-life extracted from the data is T$_{1/2}^{2ν}$= [7.15 $\pm$ 0.37 (stat) $\pm$ 0.66 (syst)] $\cdot$ 10$^{18}$ y.

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arXiv2014

Exploring the Neutrinoless Double Beta Decay in the Inverted Neutrino Hierarchy with Bolometric Detectors

Neutrinoless double beta decay (0nubb) is one of the most sensitive probes for physics beyond the Standard Model, providing unique information on the nature of neutrinos. In this paper we review the status and outlook for bolometric 0nubb decay searches. We summarize recent advances in background suppression demonstrated using bolometers with simultaneous readout of heat and light signals. We simulate several configurations of a future CUORE-like bolometer array which would utilize these improvements and present the sensitivity reach of a hypothetical next-generation bolometric 0nubb experiment. We demonstrate that a bolometric experiment with the isotope mass of about 1 ton is capable of reaching the sensitivity to the effective Majorana neutrino mass (|mee|) of order 10-20 meV, thus completely exploring the so-called inverted neutrino mass hierarchy region. We highlight the main challenges and identify priorities for an R&D program addressing them.

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arXiv2014

Discovery of the $^{151}$Eu $α$ decay

We report on the first compelling observation of $α$ decay of $^{151}$Eu to the ground state of $^{147}$Pm. The measurement was performed using a 6.15 g Li$_6$Eu(BO$_3$)$_3$ crystal operated as a scintillating bolometer. The Q-value and half-life measured are: Q = 1948.9$\pm 6.9(stat.) \pm 5.1(syst.)$ keV, and T$_{1/2}=\left( 4.62\pm0.95(stat.)\pm0.68(syst.)\right) \times 10^{18}$ y . The half-life prediction of nuclear theory using the Coulomb and proximity potential model are in good agreement with this experimental result.

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arXiv2013

Development of a Li2MoO4 scintillating bolometer for low background physics

We present the performance of a 33 g Li2MoO4 crystal working as a scintillating bolometer. The crystal was tested for more than 400 h in a dilution refrigerator installed in the underground laboratory of Laboratori Nazionali del Gran Sasso (Italy). This compound shows promising features in the frame of neutron detection, dark matter search (solar axions) and neutrinoless double-beta decay physics. Low temperature scintillating properties were investigated by means of different alpha, beta/gamma and neutron sources, and for the first time the Light Yield for different types of interacting particle is estimated. The detector shows great ability of tagging fast neutron interactions and high intrinsic radiopurity levels (< 90 \muBq/kg for 238-U and < 110 \muBq/kg for 232-Th).

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arXiv2013

Characterization of bolometric Light Detectors for rare event searches

Bolometers have proven to be very good detectors to search for rare processes thanks to their excellent energy resolution and their low intrinsic background. Further active background rejection can be obtained by the simultaneous readout of the heat and light signals produced by particles interacting in scintillating bolometers, as proposed by the LUCIFER experiment. In this framework, the choice of the light detector and the optimization of its working conditions play a crucial role. In this paper, we report a study of the performances of a Germanium bolometric light detector in terms of signal amplitude, energy resolution and signal time development. The impact of various operational parameters on the detector performances is discussed.

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arXiv2013

Performances of a large mass ZnSe bolometer to search for rare events

Scintillating bolometers of ZnSe are the baseline choice of the LUCIFER experiment, whose aim is to observe the neutrinoless double beta decay of 82Se. The independent read-out of the heat and scintillation signals allows to identify and reject alpha particle interactions, the dominant background source for bolometric detectors. In this paper we report the performances of a ZnSe crystal operated within the LUCIFER R&D. We measured the scintillation yield, the energy resolution and the background in the energy region where the signal from neutrinoless double beta decay of 82Se is expected with an exposure of 9.4 kg x days. With a newly developed analysis algorithm we improved the rejection of alpha events, and we estimated the increase in energy resolution obtained by the combination of the heat and light signals. For the first time we measured the light emitted by nuclear recoils, and found it to be compatible with zero. We conclude that the discrimination of nuclear recoils from beta/gamma interactions in the WIMPs energy region is possible, but low-noise light detectors are needed.

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arXiv2013

Sensitivity and Discovery Potential of CUORE to Neutrinoless Double-Beta Decay

We present a study of the sensitivity and discovery potential of CUORE, a bolometric double-beta decay experiment under construction at the Laboratori Nazionali del Gran Sasso in Italy. Two approaches to the computation of experimental sensitivity for various background scenarios are presented, and an extension of the sensitivity formulation to the discovery potential case is also discussed. Assuming a background rate of 10^-2 cts/(keV kg y), we find that, after 5 years of live time, CUORE has a 1 sigma sensitivity to the neutrinoless double-beta decay half-life of T_1/2(1 sigma) = 1.6 \times 10^26 y and thus a potential to probe the effective Majorana neutrino mass down to 40-100 meV; the sensitivity at 1.64 sigma, which corresponds to 90% C.L., will be T_1/2(1.64 sigma) = 9.5 \times 10^25 y. This range is compared with the claim of observation of neutrinoless double-beta decay in 76Ge and the preferred range of the neutrino mass parameter space from oscillation results.

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arXiv2012

New experimental limits on the alpha decays of lead isotopes

For the first time a PbWO4 crystal was grown using ancient Roman lead and it was run as a cryogenic detector. Thanks to the simultaneous and independent read-out of heat and scintillation light, the detector was able to discriminate beta/gamma interactions with respect to alpha particles down to low energies. New more stringent limits on the alpha decays of the lead isotopes are presented. In particular a limit of T_{1/2} > 1.4*10^20 y at a 90% C.L. was evaluated for the alpha decay of 204Pb to 200Hg.

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arXiv2012

Performances of a large mass ZnMoO4 scintillating bolometer for a next generation neutrinoless double beta decay experiment

We present the performances of a 330 g zinc molybdate (ZnMoO4) crystal working as scintillating bolometer as a possible candidate for a next generation experiment to search for neutrinoless double beta decay of 100Mo. The energy resolution, evaluated at the 2615 keV gamma-line of 208Tl, is 6.3 keV FWHM. The internal radioactive contaminations of the ZnMoO4 were evaluated as <6 microBq/kg (228Th) and 27\pm6 microBq/kg (226Ra). We also present the results of the alpha vs beta/gamma discrimination, obtained through the scintillation light as well as through the study of the shape of the thermal signal alone.

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arXiv2012

ZnMoO4: a promising bolometer for neutrinoless double beta decay searches

We investigate the performances of two ZnMoO4 scintillating crystals operated as bolometers, in view of a next generation experiment to search the neutrinoless double beta decay of Mo-100. We present the results of the alpha vs beta/gamma discrimination, obtained through the scintillation light as well as through the study of the shape of the thermal signal alone. The discrimination capability obtained at the 2615 keV line of Tl-208 is 8 sigma, using the heat-light scatter plot, while it exceeds 20 sigma using the shape of the thermal pulse alone. The achieved FWHM energy resolution ranges from 2.4 keV (at 238 keV) to 5.7 keV (at 2615 keV). The internal radioactive contaminations of the ZnMoO4 crystals were evaluated through a 407 hours background measurement. The obtained limit is < 32 microBq/kg for Th-228 and Ra-226. These values were used for a Monte Carlo simulation aimed at evaluating the achievable background level of a possible, future array of enriched ZnMoO4 crystals.

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