Giuliani.ppt
Transcript of Giuliani.ppt
Double beta decay search Double beta decay search with TeOwith TeO22 bolometers bolometers
Andrea Giulianion behalf of the CUORE collaboration
University of Insubria (Como) and INFN Milano-Bicocca
The Future of Neutrino Mass Measurements:Terrestrial, Astrophysical, and Cosmological Measurements in the Next DecadeSeattle, February 8-11, 2010
Decay modes for Double Beta DecayDecay modes for Double Beta Decay
(A,Z) (A,Z+2) + 2e- neutrinoless Double Beta Decay (0-DBD)never observed (except a discussed claim)
> 1025 y
(A,Z) (A,Z+2) + 2e- + 2e
2Double Beta Decay allowed by the Standard Model
already observed – 1019 – 1021 y
Two decay modes are usually discussed:
Double Beta Decay is a very rare, second-order weak nuclear transitionwhich is possible for a few tens of even-even nuclides
Process would imply new physics beyond the Standard Model
violation of total lepton number conservation
m 0
Observation of 0-DBD
S. Pascoli, S. T. Petcov and T. Schwetz, hep-ph/0505226
The size of the challengeThe size of the challenge
100 - 1000 counts / y ton
1 - 10 counts / y ton
0.1 - 1 counts / y ton
76Ge result
50 meV
20 meV
Electron sum energy spectra in DBDElectron sum energy spectra in DBDThe shape of the two electron sum energy spectrum enables to distinguish among the two different decay modes
Q 2-3 MeV for the most promising candidatessum electron energy / Q
two neutrino DBDcontinuum with maximum at 1/3 Q
neutrinoless DBDpeak enlarged only by
the detector energy resolution
In order to explore the inverted hierarchy region, the background in the region of interest needs to be as low as few counts / y ton
Properties of Properties of 130130Te as a DBD emitterTe as a DBD emitter
high natural isotopic abundance (I.A. = 33.87 %)
high transition energy ( Q = 2530 keV )
encouraging theoretical calculations for 0-DBD lifetime
already observed with geo-chemical techniques ( 1/2 incl = ( 0.7 - 2.7 ) 1021 y)
2 DBD decay observed by a precursor bolometric experiment (MiDBD) and by NEMO3 at the level 1/2 = ( 5 - 7 ) 1020 y
excellent feature for reasonable-cost expansion of Double Beta Decay experiments
large phase space, low background(clean window
between full energy and Compton edge
of 208Tl photons)
m 50 meV 2x1026 y
130Te features as a DBD candidate:
The bolometric technique for The bolometric technique for 130130Te: detector conceptsTe: detector concepts
Temperature signal: T = E/C 0.1 mK for E = 1 MeV Bias: I 0.1 nA Joule power 1 pW Temperature rise 0.25 mK Voltage signal: V = I dR/dT T V = 1 mV for E = 1 MeV
Noise over signal bandwidth (a few Hz): Vrms = 0.2 V Signal recovery time: = C/G 0.5 s
In real life signal about a factor 2 - 3 smaller
Energy resolution (FWHM): 1 keV
Heat sinkT 10 mK
Thermal couplingG 4 nW / K = 4 pW / mK
ThermometerNTD Ge-thermistor
R 100 MdR/dT 100 k/mK
Energy absorberTeO2 crystal
C 2 nJ/K 1 MeV / 0.1 mK
Te dominates in mass the compoundExcellent mechanical and thermal properties
A physical realization of bolometers for DBDA physical realization of bolometers for DBD
Energy absorbersingle TeO2 crystal 790 g 5 x 5 x 5 cm
Thermometer(doped Ge chip)
Cuoricino basic moduleCuoricino basic module
Cuoricino and CUORE LocationCuoricino and CUORE Location
Cuoricino was and CUORE will be installed in
Laboratori Nazionali del Gran SassoL'Aquila – ITALY
the mountain provides a 3500 m.w.e. shield against cosmic rays
R&D final tests for CUORE (hall C)
CUORE (hall A)
Cuoricino(hall A)
CUORICINO = tower of 13 modules, 11 modules x 4 detector (790 g) each
2 modules x 9 detector (340 g) eachM = 41 kg 5 x 1025 130Te nuclides
The CUORICINO set-upThe CUORICINO set-up
Cold finger
Tower
Lead shield
Same cryostatand similar
structureas previous
pilot experiment
Coldest point
CUORICINO physics resultsCUORICINO physics results
MT = 18.14 kg 130Te y
T1/20v (y) > 2.94 1024 y (90% C.L.) m < 206 – 720 meV
Background sum spectrum of all the detectors in the DBD region
use new more accurate Q-value: 2527.5 keV Phys. Rev. Lett. 102, 212502 (2009) , Phys. Rev. C 80, 025501 (2009) updated statistics through Mar 2008 (shut down in July 2008)
60Co sum peak2505 keV
3 FWHM from DBD Q-value
130Te - 0
Nucl. Phys. A 766, 107 (2006) [Erratum-ibid. A 793, 213 (2007)]
BKG rate: 0.180.01 counts / keV kg y
CUORE = closely packed array of 988 detectors 19 towers - 13 modules/tower - 4 detectors/moduleM = 741 kg 1027 130Te nuclides
Compact structure, ideal for active shielding
From CUORICINO to CUOREFrom CUORICINO to CUORE((CCryogenic ryogenic UUnderground nderground OObservatory for bservatory for RRare are EEventsvents))
Each tower is a CUORICINO-like detectorCustom dilution refrigerator
2008 2009 2010 2011 2012
HUT
CRYSTALS
OTHER DETECTOR ELEMENTS (THERMISTORS, HEATERS, HOLDERS…)
CRYOSTAT
CLEAN ROOM
CUORE-0 PREPARATION
ASSEMBLY AND INTEGRATION
DATA TAKING
The CUORE scheduleThe CUORE schedule
CUORE-0 RUNNING
Background in 0 region10-2 c/keV/kg/y
T1/20 (130Te) > 2.1 x 1026 ymββ < 44 - 73 meV
Background in 0 region10-3 c/keV/kg/y
T1/20 (130Te) > 6 x 1026 y
mββ < 25 - 43 meV
Surface background problem partially / fully
solved
IBM2 44 meVQRPA Jyuvaeskulae 49 meVQRPA Tuebingen et al. 53 meVISM 73 meV
IBM2 25 meVQRPA Jyuvaeskulae 29 meVQRPA Tuebingen et al. 31 meVISM 43 meV
Detector resolution 5 keVLive time 5 years
More recent and reliable NME calculations
CUORE sensitivityCUORE sensitivity
Simulation of the external backgroundSimulation of the external background
Cuore external background - arXiv:0912.0452v2 – accepted by Astroparticle Physics
The CUORE background componentsThe CUORE background components
Component Background in DBD region( 10-3 counts/keV kg y )
External gammas
Apparatus gammas
Crystal bulk
Crystal surface
Close-to-det. material surface
External neutrons
Muons
< 0.39
< 1
< 0.1
< 3
< 1
20 – 40
0.270 ± 0.022 (8.56 ± 6.06)×10−3
17.3 ± 0.3 0.104 ± 0.022
Close-to-det. material bulk
Total Anticoincidence
The Cuoricino background and the alpha surface radioactivityThe Cuoricino background and the alpha surface radioactivity
214Bi
60Co p.u.
208Tl~ 0.11 c / keV kg y
Gamma region
(A) Action on the source surface cleaning – plastic wrapping
(B) Action on the detectors events identification
Mechanical action / Electropolishing Chemical etching / Plasma cleaning
“Legnaro” cleaning method [CUORE baseline]
“Gran Sasso” cleaning method
Composite surface sensitive bolometers
Strategies for the control of the surface background from inert Strategies for the control of the surface background from inert materials materials
Polyethelene wrapping
Thin-film equipped surface sensitive bolometers
Cherenkov light for beta identification
Strategy adopted by the CUORE collaboration to
reject surface background
Possible R&D subjects aiming at fully exploiting the potential of TeO2 bolometers in a second phase
(A) Surface-radioactivity source control: state of the art(A) Surface-radioactivity source control: state of the artThree-tower run: direct comparison of the three methods for source control
WrappingWrapping
Gran Gran SassoSasso
LegnaroLegnaro
Prelim
inary
Prelim
inary
Results:The three methods are similar, but Legnaro and wrapping are better: baseline option is confirmed.
Raw background in 3-4 MeV region: 0.06-0.07 counts/keV kg y
Safe and conservative extrapolation for CUORE background in region:
0.04 counts/keV kg y
Action on the detectorsAction on the detectors
Some personal considerations on plausible options
to reject the surface background
(B) Event identification: composite surface sensitive bolometers(B) Event identification: composite surface sensitive bolometersProtect each crystal surface with a thin auxiliary bolometer and read out simultaneous signal from the main and the auxiliary bolometer a scatter plot separates surface and bulk events
Two TeO2 auxiliary bolometers are read in parallel
Pulse amplitude
Pulse amplitudebetas+gammas
alphas
X
The thermistor on the thin absorber is removed: the slab works as a signal shape modifier
Pulse decay time
Pulse amplitude
210Pb contamination monochromatic alphas
bulk events
Dramatic simplification Underground tests performed on CUORE
size elementary modules
Encouraging but not conclusive results
It is worthwhile to study systematically this approach
Appl. Phys. Lett. 86,134106(2005)
Nucl. Instr. Meth. A559, 355 (2006)
TeO2
TeO2
(B) Event identification: thin-film equipped surface sensitive bolometers(B) Event identification: thin-film equipped surface sensitive bolometers Deposit on each crystal surface a NbSi thin film which works as temperature sensor, but is sensitive to athermal phonons for surface events PSD separates surface and bulk events
Pulse shape parameter
Pulse amplitude
It works in small TeO2 prototype, but unpractical
Six independently read out films are required Specific heat of NbSi is high, difficult to work at 10 mK
bulk
surface
5.4 MeV alpha
60 keV gamma
NbSi film J. Low Temp. Phys. 151, 871 (2008)
Deposit a passive film on each surface and read out TeO2 temperature with ordinary sensorDramatic
simplificationThe goal is to get a shape-changed signal when part of the energy is released in or near the deposited film film as a pulse shape modifier Rely on purely thermal effect play with film material (heat capacity) and film-crystal thermal conductance Same approach as slab addition, but cleaner and more reproducible Exploit quasi-particle life-time in a superconductive film (e.g. Al)
Pulse shape At the center of a two-year program of
a Marie Curie fellowship [ARBRES]
TeO2
TeO2
(B) Event identification: Cherenkov light for electron tagging(B) Event identification: Cherenkov light for electron tagging
Optical properties of TeO2 crystals Transparent from 350 nm to infrared n=2.4
Threshold for Cherenkov emission:50 keV for an electron400 MeV for an alpha particle
Cherenkov effect is potentially able to discriminate betas from alphas!
How many photons in the 2 - 3.5 eV interval?
125 photons for a decay event
It looks within the reach of the bolometric light detectors developed for Dark Matter (CRESST)
Caution: scintillation light for TeO2 was claimed several years ago Nucl. Instr. Meth. A 520 159 (2004)
The results for a gamma calibration seems compatible with Cherenkov light emission BUT a small light yield from alpha particle (a few photons/5MeV) suggests that also scintillation is present.Anyway, the beta/gamma light yield ratio is of the order of 25
Attempts to increase low temperature scintillation in TeO2 by Nb and Mn doping failed
Eur. Phys. J. C 65, 359 (2010)
CUORE sensitivity with improved TeOCUORE sensitivity with improved TeO22 bolometers bolometers
Assumptions for CUORE upgrade:
TeO2 (isotope: 130Te)Successful R&D (enriched crystals and alpha tagging) BKG in DBD region = 1x10-3 counts/keV kg yEnrichment cost: 15 €/g at 99%
mββ
Sensitivity to mββ (QRPA-Tuebingen et al.) as a function of the enrichment cost and detector mass35
30
25
20
15200 400 600 800 10002 4 6 8 10 12
(mββ)[meV]
Enrichment cost [M€]Detector total mass [kg]
Maximum occupation of
CUORE cryostat
ConclusionsConclusions
TeO2-based bolometers represent a well established technique, very competitive for neutrinoless double beta decay search
Cuoricino, stopped in 2008, is one of the most sensitive double beta decay search ever run
Cuoricino demonstrates the feasibility of a large scale bolometric detector (CUORE) with high energy resolution and competitive sensitivity (approaching the inverted hierarchy region)
CUORE, a next generation detector, is under construction and will start to take data in 2012/2013
The CUORE sensitivity can be extended to cover fully the inverted hierarchy region with enrichment and rejection of surface radioactivity → the TeO2 approach is highly competitive in general and in the specific field of bolometric searches