Transcript The CUORE experiment Thomas Bloxham Lawrence Berkeley National Lab PHENO 2011 May 9th 2011

The CUORE experiment
Thomas Bloxham
Lawrence Berkeley National Lab
PHENO 2011
May 9th 2011
Contents
Neutrinoless Double  decay
 Sensitivity
 CUORE and it’s prototypes
 Progress

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Neutrinoless Double  Decay
Intermediate
FinalA,Z
A,Z+2
virtual
nucleus
nucleus
A,Z+1 nucleus
e
e
e
anti-neutrino
anti-neutrino
neutrino
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Neutrinoless Double  Decay



There 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.
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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
2
T

a
F
M

 1/ 2,0  0 0 0 /log2
1


2
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.
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Sensitivity
Detector Mass(kg)
Measuring Time (yrs)
a.i. M  t meas
S( )   
A E  bkg
0
1/ 2
Background
(cts/(keV yr kg)
Detector Efficiency
Isotopic Abundance
Atomic Mass Number
Resolution(keV)
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Candidate Nuclei


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130Te
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 208Tl
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The CUORE experiment



The 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.
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Bolometric Techniques
Cv 
12 4 Nk
5TD3
T
3
Detector Working Temperature = 10 mK
Heat capacity = 2*10-9 J/K (750 g detector at 10 mK)

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Bolometric Advantages
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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 it’s source particle
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The LNGS location
1.4 km rock overburden equivalent to 3100 ± 200 meters of
water
Neutron Flux = ~4*10-6 neutrons/(cm2 s)
Muon Flux = (2.58±0.3)*10-8 muons/(cm2 s)
CUORE
R&D
CUORICINO
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CUORICINO
BKG@ROI = 0.169 ± 0.005 cts / (keV kg yr)
19.75 kg (130Te) yrs of exposure
2ν mode: T1/2(2ν) ~= 0.9 ± 0.15 ⋅ 1021 yr A. S. Barabash,
Czech. J. Phys. 52, 567-573 (2002)
0ν mode: T1/2(0ν) > 2.8⋅ 1024 yr @ 90% C.L.
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CUORE

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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
CUORE’s mass provides benefits in more ways than simply
increasing the rate of increase in detector exposure. Anticoincidence 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.
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CUORE Improvements
CUORE
CUORICINO
Data taking
Continuous Data
Stream
Triggered events
Channels
988
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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
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CUORE Improvements
CUORE
CUORICINO
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
Mass
740 kg TeO2
40.7 kg TeO2
Tower Assembly
More automation,
nitrogen flushed glove
boxes, radon free final
assembly area
Manual, sometimes
exposed to air
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Timeline and mass progression
preliminary
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CCVR tests
preliminary
•CCVR tests each tested a small
sample of recently produced
bolometer crystals
•They used the same electronics
and mounting procedure as
CUORE will use
preliminary
Both contaminant levels below contracted
requirements
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Conclusions

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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 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
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Thanks for listening
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