The CUORE experimentThomas BloxhamLawrence Berkeley National LabPHENO 2011May 9th 2011

ContentsNeutrinoless Double decaySensitivityCUORE and its prototypesProgress

Neutrinoless Double Decayeeeeanti-neutrinoanti-neutrinoA,Z nucleusIntermediate virtual A,Z+1 nucleusFinal A,Z+2 nucleusneutrino

Neutrinoless Double DecayThere is a great deal of experimental effort ongoing in an attempt to observe this decay in a variety of elements (130Te in CUORE,116Cd in COBRA, 76Ge in Majorana and GERDA, 136Xe in KamLAND-xen)The primary interest however is determining whether the character of the neutrino is Dirac or Majorana.However, it is possible to gain more information from the rate of this decay if observed, in that the rate of this decay is proportional to the mass of the neutrino.

Neutrino MassThe difficulty in doing this however is that while the occurrence of the decay is an immediate indicator of Majorana character, the conversion from half life to mass requires this equation

Here M0v is an unknown matrix element relating rate and mass. Current determinations from theory are rather varied, and form a major part of all of the errors quoted on mass limits provided by current experiments.

Sensitivity

Candidate Nuclei130Te has a Q value of approximately 2528 keV, and a natural abundance of 34.2%Its matrix elements compare favorably with all other candidatesIts Q value is above most background gamma lines other than 208Tl

The CUORE experimentThe CUORE experiment is a Bolometric search for neutrinoless double decay using 988 TeO2 crystals arranged in 19 towers.With currently expected backgrounds of 10-2 ~ 10-3 counts/kg keV year in the region of interest the full scale experiment should be able to produce a competitive mass limit for the neutrino within the first year.A variety of prototypes have already been operated and best limits for many decays have already been set using Bolometric techniques in these detectors.

Bolometric TechniquesDetector Working Temperature = 10 mKHeat capacity = 2*10-9 J/K (750 g detector at 10 mK)

Bolometric AdvantagesBolometric techniques for neutrinoless double beta decay lend themselves well to source as detector techniques, maximizing efficiencyThey have an intrinsically good resolution which improves further as temperature fallsThey function well as large detectors, allowing a single channel to instrument a large amount of mass. This limits the amount of instrumentation required in a low counting rate experiment.They can be made from a wide variety of materialsThey are true calorimeters, and respond identically to energy deposited regardless of its source particle

The LNGS locationMuon Flux = (2.580.3)*10-8 muons/(cm2 s)Neutron Flux = ~4*10-6 neutrons/(cm2 s)1.4 km rock overburden equivalent to 3100 200 meters of water

CUORICINO0 mode: T1/2(0) > 2.8 1024 yr @ 90% C.L. 2 mode: T1/2(2) ~= 0.9 0.15 1021 yr A. S. Barabash, Czech. J. Phys. 52, 567-573 (2002)BKG@ROI = 0.169 0.005 cts / (keV kg yr)19.75 kg (130Te) yrs of exposure

CUOREThe lessons learned from CUORICINO have been used to produce a design for CUORE which should hugely improve on the capacity of the prototype.The improvements in CUORE are both in terms of sheer size, and in terms of the background goals for the experiment. To succeed CUORE must lower background by a factor of at least 20 over CUORICINOCUOREs mass provides benefits in more ways than simply increasing the rate of increase in detector exposure. Anti-coincidence vetoing with CUORE will be more effective at removing background, and bolometers at the core of the detector should be shielded from contaminants on the cryostat wall.

CUORE Improvements

CUORECUORICINOData takingContinuous Data StreamTriggered eventsChannels98862Mounting and gluing of thermistorsRobotic gluing and assembly in clean roomManual gluing, assembly in clean roomCopper in facing surfacesNew design reduces amount of copper facing crystals by halfOld holder design

CUORE Improvements

CUORECUORICINOCrystal surface cleaningNew protocol reduces background from this source 75%Old methodCopper surface contaminationLegnaro method designed by collaboration cuts background 50%Old cleaning methodMass740 kg TeO240.7 kg TeO2Tower AssemblyMore automation, nitrogen flushed glove boxes, radon free final assembly areaManual, sometimes exposed to air

Timeline and mass progression

CCVR testspreliminarypreliminaryBoth contaminant levels below contracted requirements CCVR tests each tested a small sample of recently produced bolometer crystalsThey used the same electronics and mounting procedure as CUORE will use

ConclusionsThe CUORE experiment is at the forefront of the next generation of detectors designed to detect neutrinoless double beta decay.It is uniquely placed to exploit a detection method in bolometry which is the only experimental technique with a good enough resolution to effectively remove neutrino accompanied double beta decay as a backgroundThe natural abundance of 130Te also frees the experiment from having to enrich vast amounts of material, allowing it to be the detector observing the largest mass of neutrinoless double beta decay isotopes.Construction and testing is proceeding apace, and data taking with CUORE-0, which will begin this year, will in and of itself serve as not only a proof of concept but as the most sensitive test to date of the existence of neutrinoless double beta decay

Thanks for listening

Neutrinoless double beta decay is comparatively easy to see if you capture both electrons, as they will have a precisely defined total energy and show up as a sharp peak at the Q value, as opposed to neutrino accompanied reactions were the total electron energy peaks lower than the Q value due to energy being lost to the neutrino escapes.

Neutrinoless double beta decay is forbidden by the standard model, detecting it would be evidence for new physics beyond the standard model. Neutrino accompanied decay is a second order weak decay only observable in even-even nuclei due to pairing effects.a0 ~ 5 10-17 y-1 is a dimensional factor F0 is a known phase space factor proportional to Q5 M0 is the nuclear matrix element (n.m.e.).

= /me with being the effective mass of the exchanged neutrino and me the mass of the electron (0.511 MeV/c2). The experiment requires.High efficiency for detection of a decayHigh Abundance of the target isotopeGood resolution to remove background in the region of interest, and sharpen the peakLow background in the region of interestMassive detectors, observing close to the ton scale of materialTD is the Debeye temperature, which is about 153 K for TelluriumCv is the heat capacityThe crystals also have a small heater mounted on them for calibrationLarge bolometer crystals tested thus far in CUORICINO have had a resolution of ~6.3 KeV +- 2.5 keV.The detectors also have a small heater element mounted on them for thermal calibration.A 2.6 MeV event will heat up the 750 gram mass by 0.2 mKDisadvantages. Long pulse time (on the order of 5 seconds of capture time for a peakStable cryogenic environment requirement (~10 mK and stable at that level with limited drift)No position sensitivity in basic design, some future designs hope to achieve this using additional data channelsSurface muon flux is ~ 0.013 muons/m2 sCUORICINO was a prototype CUORE experiment which was also a world best experiment in its own right, instrumenting about 40.7 Kg of Tellurium.

It included crystals enriched in 130 Te to evaluate the benefits of doing this and to improve sensitivity to neutrino accompanied double beta decay.

It operated until 2010, when it was shut down to make way for tests moving towards the CUORE experiment (three towers test)

Black = Background spectrumRed = Calibration spectrum normalized to Tl-208 peak.1 - e+e- annihilation2 - 214Bi3 - 40K4 - 208Tl5 - 60Co6 - 228Ac Crystal surface cleaning is now done with ultra pure HNO3 and ultra pure Si02 powderCopper contamination was checked with a dedicated three towers test which instrumented 24 bolometers in three different copper shields. Each was a new method, and each was comparable to the others. So, the simplest method was selected.Comment on how CUORE-0 will also happenComment that we are currently in year 10.

Bolometric performance and surface/bulk contamination were tested