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The CUORE experiment Thomas Bloxham Lawrence Berkeley National Lab PHENO 2011 May 9th 2011 Slide 2 2 Contents Neutrinoless Double decay Sensitivity CUORE and its prototypes Progress Slide 3 3 Neutrinoless Double Decay e e e e anti-neutrino A,Z nucleusIntermediate virtual A,Z+1 nucleusFinal A,Z+2 nucleus neutrino Slide 4 4 Neutrinoless Double Decay There is a great deal of experimental effort ongoing in an attempt to observe this decay in a variety of elements ( 130 Te in CUORE, 116 Cd in COBRA, 76 Ge in Majorana and GERDA, 136 Xe 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. Slide 5 5 Neutrino Mass The 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 M 0v 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. Slide 6 6 Sensitivity Detector Efficiency Isotopic Abundance Atomic Mass Number Detector Mass(kg) Resolution(keV) Background (cts/(keV yr kg) Measuring Time (yrs) Slide 7 7 Candidate Nuclei 130 Te has a Q value of approximately 2528 keV, and a natural abundance of 34.2% Its matrix elements compare favorably with all other candidates Its Q value is above most background gamma lines other than 208 Tl Slide 8 8 The CUORE experiment The CUORE experiment is a Bolometric search for neutrinoless double decay using 988 TeO 2 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. Slide 9 9 Bolometric Techniques Detector Working Temperature = 10 mK Heat capacity = 2*10 -9 J/K (750 g detector at 10 mK) Slide 10 10 Bolometric Advantages Bolometric techniques for neutrinoless double beta decay lend themselves well to source as detector techniques, maximizing efficiency They have an intrinsically good resolution which improves further as temperature falls They 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 materials They are true calorimeters, and respond identically to energy deposited regardless of its source particle Slide 11 11 The LNGS location R&D CUORE CUORICINO Muon Flux = (2.580.3)*10 -8 muons/(cm 2 s)Neutron Flux = ~4*10 -6 neutrons/(cm 2 s) 1.4 km rock overburden equivalent to 3100 200 meters of water Slide 12 12 CUORICINO 0 mode: T1/2(0) > 2.8 10 24 yr @ 90% C.L. 2 mode: T 1/2 (2) ~= 0.9 0.15 10 21 yr A. S. Barabash, Czech. J. Phys. 52, 567-573 (2002) BKG@ROI = 0.169 0.005 cts / (keV kg yr) 19.75 kg ( 130 Te) yrs of exposure Slide 13 13 CUORE The 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 CUORICINO CUOREs 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. Slide 14 14 CUORE Improvements CUORECUORICINO Data takingContinuous Data Stream Triggered events Channels98862 Mounting and gluing of thermistors Robotic gluing and assembly in clean room Manual gluing, assembly in clean room Copper in facing surfaces New design reduces amount of copper facing crystals by half Old holder design Slide 15 15 CUORE Improvements CUORECUORICINO Crystal surface cleaning New protocol reduces background from this source 75% Old method Copper surface contamination Legnaro method designed by collaboration cuts background 50% Old cleaning method Mass740 kg TeO 2 40.7 kg TeO 2 Tower AssemblyMore automation, nitrogen flushed glove boxes, radon free final assembly area Manual, sometimes exposed to air Slide 16 16 Timeline and mass progression preliminary Slide 17 17 CCVR tests preliminary Both contaminant levels below contracted requirements CCVR tests each tested a small sample of recently produced bolometer crystals They used the same electronics and mounting procedure as CUORE will use Slide 18 18 Conclusions The 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 background The natural abundance of 130 Te 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 Slide 19 19 Thanks for listening