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CUORE (Cryogenic Underground Observatory for Rare Events) is a particle physics facility located at the Laboratori Nazionali del Gran Sasso in Italy. It uses a tellurium dioxide crystal bolometer-thermistor detector to search for neutrinoless double beta decay (0νββ) in 130Te. Observing such decays would mean that neutrinos are their own antiparticles and Majorana fermions. This is relevant to many topics in particle physics: lepton number conservation, nuclear structure, as well as neutrino masses and properties. CUORE searches for a spike in the tellurium decay spectrum around the known decay energy of Q = 2527.518±0.013 keV, that would be evidence of 0νββ events. The detector is expected to be sensitive enough to also be used in searches for axion signals and dark matter.

The CUORE collaboration involves physicists from several countries including the US and Italy, and has published papers on the performance of various parts of the detector and simulation. CUORE is primarily funded by the Istituto Nazionale di Fisica Nucleare (INFN) of Italy, the United States Department of Energy (DOE), and the National Science Foundation (NSF) of the United States.

In September 2014, CUORE researchers cooled a copper vessel inside the detector with a volume of one cubic meter to 6 mK for 15 days, setting a record for the lowest temperature in the known universe over such a large contiguous volume.

CUORICINO
The CUORICINO prototype was built to determine if backgrounds could be reduced enough to study neutrinoless double-beta decay. The experiment ran between 2003 and 2008 at the Gran Sasso National Laboratory. In the course of its operation, it yielded a total exposure of 19.75 kg*y of 130Te. The experiment set with 90% confidence a lower limit on the neutrinoless double-beta decay half-life of 130Te to be 2.8 x 1024 years. The experiment was comprised of 62 enriched and unenriched TeO2 crystals for a total TeO2 mass of 40.7 kg that equates to 11.3 kg of 130Te.

CUORICINO operated in the underground facilities of the Gran Sasso laboratory from 2003 until 2008. The bolometer was operated at a temperature of 10 mK over the course of data collection. The dilution refrigerator was the primary mechanism used to maintain this temperature. Each bolometer crystal had mounted to it a Neutron Transmutation Doped Germanium Thermistor to measure energy changes in the crystals.

The detector crystals were arranged in a single tower of thirteen floors. There were four forms of crystal used. The first crystal type was a 5 cubic centimeter cube of 130Te that weighed 790 g and of natural abundance. The second crystal type was a 3 cm x 3 cm x 6 cm cube of 130Te weighing 330 g of natural abundance of 34.2%. The third crystal type was a 3 cm x 3 cm x 6 cm cube of 130Te weighing 330 g enriched to 75% abundance. The fourth crystal type was a 3 cm x 3 cm x 6 cm cube of 128Te weighing 330 g and enriched to 82% abundance. Eleven floors of the tower consisted of four of the first type of crystal. The other two floors each consisted of nine of the smaller crystals. The tower was supported by a copper skeleton. Each crystal was attached to that skeleton by Teflon supports.

Environmental radioactivity and electrical noise was reduced via the use of four shielding mechanisms. The outermost shield was a Faraday cage used to eliminate electrical noise. The next most inner shield was a 20 cm thick layer of borated polyethylene used to reduce neutron flux. The next most inner shield was a 20 cm thick layer of commercial lead. The innermost layer was a 1 cm thick layer of 130Pb of radioactivity less than 4 mBq/kg. Radon contamination was mitigated by over-pressurizing the detector atmosphere with nitrogen gas.

CUORICINO placed an upper limit on the effective majorana mass of 0.300 - 0.710 eV. The experiment also identified the predominant background sources in the region of interest as alpha particles originating on the copper skeleton and on other cryostat surfaces. The desired background of CUORE is 0.01 count/(keV*y*kg). CUORICINO determined that all contributing backgrounds could be reduced to meet that goal except for the alpha particles originating on the copper skeleton. Thus, it was determined that a different means of account for these alpha particles was necessary.

The experiment placed a lower limit on the half-life for normal double-beta decay and neutrinoless double-beta decay in 130Te. For the normal double-beta decay mode, CUORICINO found a lower limit of T$2v (1/2)$ > 1.3 x 1023 with a 90% confidence level. For the neutrinoless double-beta decay mode, the experiment found T$0v (1/2)$ > 2.8 x 1024 with a 90% confidence level.

CUORE-0
The CUORE-0 experiment was constructed to test the CUORE experiment assembly line and to check improvements of the bolometric apparatus and radioactive background reduction strategies over the CUORICINO experiment. CUORE-0 confirmed the design and process improvements for the CUORE array before the array's production.

CUORE-0 consists of a single tower of 52 TeO2 crystals housed in a copper skeleton. The tower is arranged into thirteen floors with four crystals on each floor. Each crystal has a mass of 750 g. This tower is housed in the same cryostat which previously housed the CUORICINO experiment. The experiment first began taking data in March of 2013.

Part of the CUORE-0 experiment was the implementation of a strict set of protocols designed to minimize the radioactive contamination of detector materials during production and assembly.

As of February 9, 2015 the CUORE-0 experiment has yielded a total exposure of 18.1 kg*y to TeO2.

CUORE
CUORE will be the flagship experiment for the detection of neutrinoless double-beta decay. The experiment will consist of 19 identical towers of TeO2 crystals. A total of 988 identical crystals will be used in the experiment. Each tower has thirteen floors with four crystals on each floor.

Gran Sasso d'Italia
The CUORE experiment is located at the Laboratori Nazionali del Gran Sasso (LNGS). This lab is located in the L'Aquila region of Italy immediately adjacent to the town of Assergi. However, the property technically is within the boundaries of the Parco Nazionale del Gran Sasso e Monti della Laga. The park contains several peaks of the Apennine Mountain Range including "Corno Grande," the highest peak of the range on the Italian peninsula. The park is also home to the Hotel Campo Imperatore, the site of the historical Gran Sasso raid where the Italian dictator Benito Mussolini was rescued by German paratroopers during World War II. The park also was the location used for the filming of the american movie Ladyhawke. Immediately adjacent to the lab is the Autostrada A24, also known as the "Autostrada dei Parchi" or "Motorway of the Parks" which traverses the park between L'Aquila and Teramo and serves as the entrance to the underground facilities. The area surrounding the lab is often praised for its agricultural products and captivating landscapes.

Above-ground Facilities
The administrative offices, research offices, auditorium, cafeteria, café, electronics lab, chemistry lab, machine shop, warehouse, research library, museum, and several research and development labs of the Gran Sasso National Laboratory are located above-ground near the periphery of the town of Assergi. A shuttle runs daily between the above-ground and underground facilities for the transportation of users.

Underground Facilities
The major experiments being conducted at the Gran Sasso National Laboratory have their facilities located in the underground part of the laboratory. The entrance to the lab is an exit of the westbound portion of the A24 motorway. The underground facilities are located below the Corno Grande mountain peak in order to maximize the shielding effects of the mountain rock from cosmic rays and particles. The facility is divided into three major halls which house the detectors - Hall A, Hall B, and Hall C. The CUORE and CUORE-0 detectors are located in Hall A.

Construction
The CUORE Detectors TeO2 crystals are known to produce beta decay as low heat capacity bolometers. These crystals are contained in copper towers and chilled in cryostats to ~10mK. The towers are isolated from environmental thermal, electromagnetic, and particle influences by ultra-pure low-radioactivity shielding. Temperature spikes from Te beta decays are collected for spectrum analysis. 232Th, a gamma emitter with lines up to 2615 keV, is used to calibrate the detectors.

Considerable effort went into minimizing radioactive contamination in the detector materials because such contamination produces a background noise in the detector. The crystals were grown by Shanghai Institute of Ceramics for radio-purity. Neutron-doped Ge thermistors, oxygen-free copper, N2 flushing, and clean rooms, were used in construction and assembly minimize particles. Impurities(214Bi, 40K, 208Tl, 60Co, and 228Ac) in the experiment and environment emit α and γ rays into the detectors. Roman Lead and Borated-polyethylene are used for shielding for gamma rays and neutrons. Coincidence algorithms have been used to reject these signals from nearby crystals and other methods are being developed.

Coldest Temperature Mass Product in Known Universe
In 2014, the CUORE cryostat was cooled to 10 mK in a test cool-down. The cryostat successfully reached that temperature and in doing so cooled over one cubic meter of matter to under 50mK. At that time, the matter under 50mK became the coldest cubic meter in the known universe.

Upon completion of the commissioning of the CUORE detector, the detector will again be cooled for data-taking. At this time, the CUORE detector is expected to again break the coldest temperature record and set others. For one, the 741 kg of target material occupying 636 L will be cooled to under 10 mK - this will be the coldest amount of matter of that size and density in the known universe.

CUORICINO
CUORICINO, the first detector, ran April 2003 to June 2008. Final results using 19.75 kg·y of 130Te, set a 90% limits: $T ½ 0νββ$ ≥ 2.8×1024 yr, mν ≤ 710 eV, with a background count of 0.18±0.01/(keV·kg·yr). Axion mass limits were also set.

CUORE-0
CUORE-0 initial performance was published in Aug 2014 using data taken March to September 2013, with 7.1 kg·y exposure, showing backgrounds reduced by a factor of six over the CUORICINO experiment, and energy resolution of 5.7 keV. CUORE-0 reduced background to 0.019 ± 0.002 counts/(keV·kg·y), and is expected to surpass the CUORICINO bound after one year of data, with results expected in 2015.

CUORE
CUORE will have 988 crystals in 19 similar towers and a background goal of 0.01·counts/(keV·kg·y). After 5 years, they expect to have a 90% CL half-life sensitivity of: 9.5×1025 yr, and mass sensitivity of 0.13 meV, which overlaps the inverted neutrino hierarchy.

Institutions
The departments, groups, and institutions of author's listed at some time on CUORE publications are listed below:


 * Department of Physics and Astronomy, University of South Carolina, Columbia, SC 29208, USA
 * INFN, Laboratori Nazionali del Gran Sasso, Assergi, 67010 L’Aquila, Italy
 * INFN, Laboratori Nazionali di Legnaro, Legnaro, 35020 Padova, Italy
 * Department of Physics, University of California, Berkeley, CA 94720, USA
 * Nuclear Science Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA
 * INFN, Sezione di Bologna, 40127 Bologna, Italy
 * Materials Science Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA
 * Dipartimento di Fisica, Sapienza Università di Roma, 00185 Roma, Italy
 * INFN, Sezione di Roma, 00185 Roma, Italy
 * INFN, Sezione di Genova, 16146 Genova, Italy
 * Dipartimento di Fisica, Università di Milano-Bicocca, 20126 Milano, Italy
 * INFN, Sezione di Milano Bicocca, 20126 Milano, Italy
 * Shanghai Institute of Applied Physics, Chinese Academy of Sciences, Shanghai 201800, China
 * Dipartimento di Fisica, Università di Genova, 16146 Genova, Italy
 * Department of Physics, University of Wisconsin, Madison, WI 53706, USA
 * INFN, Laboratori Nazionali di Frascati, Frascati, 00044 Roma, Italy
 * Centre de Spectrométrie Nucléaire et de Spectrométrie de Masse, Orsay Campus, 91405 Orsay, France
 * Physics Department, California Polytechnic State University, San Luis Obispo, CA 93407, USA
 * Department of Materials Science and Engineering, University of California, Berkeley, CA 94720, USA
 * Department of Physics, Yale University, New Haven, CT 06520, USA
 * Department of Physics and Astronomy, University of California, Los Angeles, CA 90095, USA
 * Physics Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA
 * Lawrence Livermore National Laboratory, Livermore, CA 94550, USA
 * Laboratorio de Fisica Nuclear y Astroparticulas, Universidad de Zaragoza, 50009 Zaragoza, Spain
 * Service de Physique des Particules, CEA/Saclay, 91191 Gif-sur-Yvette, France
 * Department of Nuclear Engineering, University of California, Berkeley, CA 94720, USA
 * INFN, Sezione di Padova, 35131 Padova, Italy
 * Dipartimento di Fisica, Università di Firenze, 50125 Firenze, Italy
 * INFN, Sezione di Firenze, 50125 Firenze, Italy
 * SUPA, Institute for Astronomy, University of Edinburgh, Blackford Hill, Edinburgh EH9 3HJ, UK
 * Dipartimento di Fisica, Università di Bologna, 40127 Bologna, Italy

Funding
CUORE is largely funded by contributions from the United States Department of Energy, the Istituto Nazionali di Fisica Nucleare, the National Science Foundation, the University of Wisconsin Foundation and the Alfred P. Sloan Foundation. The experiment also has utilized resources of the National Energy Research Scientific Computing Center

The National Science Foundation grant numbers supporting CUORE are:
 * NSF-PHY-0605119 ($1,569,617.00)
 * NSF-PHY-0500337 ($959,990.00)
 * NSF- PHY-0855314 ($1,060,338.00)
 * NSF-PHY-0902171 ($730,000.00)
 * NSF-PHY-0969852 ($231,203.00)

The Department of Energy contract numbers supporting CUORE are:
 * DE-AC02-05CH11231
 * DE-AC52-07NA27344
 * DE-FG02-08ER41551
 * DE-FG03-00ER41138

Experiment Timeline

 * 2003 - 2008: CUORICINO experiment is conducted.
 * March, 2013 - Present: CUORE-0 experiment is conducted.
 * 2015: CUORE expected to take first data.

ABSuRD
ABSuRD is "A Background Surface Rejection Detector" research and development project for the CUORE detector. The project aims to develop a scintillating bolometer with the ability to veto ionizing background radiation. The experiment involves the development of thin film plastic scintillators which would be used to cover the crystals of the CUORE bolometer for the tagging of incident alpha radiation. An initial round of films has been developed in cooperation with Brookhaven National Lab.

The experiment anticipates the need to successfully tag degraded alpha radiation with kinetic energy as low as 1.5 MeV which may be present in the CUORE detector. The tagging method would begin with the production of scintillation light as the alpha particle passes the thin film scintillator and then deposits its energy onto the bolometer crystal. That scintillation light would then be detected by a photomultiplier which would produce a veto signal for the event. Currently, Silicon Photomultipliers are being investigated for their use as the photomultiplier.

This research and development project is being conducted at the above-ground facilities of LNGS. Currently, the light activity, transmittance, and energy thresholds of the film scintillators are being characterized at cryogenic temperatures.

Enriched Crystals
One proposed method for improving the research efficacy of the experimental apparatus is to utilize "enriched" tellurium dioxide bolometer crystals. The crystals currently utilized have an isotopic abundance of about 33.8%. The proposed enriched crystals would have an isotopic abundance of 92%.

Public Outreach
Researchers of the CUORE experiment volunteer their time at the annual "Open Day" of LNGS. The event welcomes the public into the lab for tours and other activities. The event is designed to inspire scientific curiosity in youth through events ranging from the youth science fair to planetarium tours.

Links

 * Main CUORE page
 * CUORE at LNGS
 * Berkeley group CUORE page
 * Main CUORICINO page
 * LNGS Website

Category:Neutrino experiments Category:Particle experiments