Neutrino masses from double beta decay

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Neutrino masses from double beta decay

• Kai ZuberUniversity of Sussex

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Contents

• Introduction
• Double beta decay
• COBRA
• Outlook
• Summary and conclusions

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Neutrino masses from cosmology
New WMAP measurement SDSS data
Mass bound model dependent, currently done within
?CDM
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Neutrinos in cosmology
M. Tegmark
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Combined SDSS and WMAP data
M. Tegmark et al., Phys. Rev. D 69, 103501 (2003)
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Neutrino mass from cosmology
O. Lahav, Neutrino 2004

Data Authors mn S mi
2dFGRS Elgaroy et al. 02 lt 1.8 eV
WMAP2dF Spergel et al. 03 lt 0.7 eV
WMAP2dF Hannestad 03 lt 1.0 eV
SDSSWMAP Tegmark et al. 04 lt 1.7 eV
WMAP2dF SDSS Crotty et al. 04 lt 1.0 eV
Clusters WMAP Allen et al. 04 0.560.30-0.26 eV
All upper limits 95 CL, but different assumed
priors !
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Oscillation evidences
LSND
sin2 2? 10-1-10-3 , ?m2 0.1-6 eV2
Atmospheric
sin2 2? 1.00 , ?m2 2.1 ? 10-3 eV2
Solar reactors
sin2 2? 0.81 , ?m2 8.2 ? 10-5 eV2
If all three are correct... we need more (sterile
ones)
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Neutrino mass schemes
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Neutrinos mass density
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Contents

• Introduction
• Double beta decay
• COBRA
• Outlook
• Summary and conclusions

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Double beta decay
-

• (A,Z) ? (A,Z2) 2 e- 2?e 2???

• (A,Z) ? (A,Z2) 2 e- 0???

0
In nature there are 35 isotopes
2??? Seen in 10 isotopes, important for nuclear
physics input
0??? Only possible if neutrinos are Majorana
particles
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Spectral shapes
0??? Peak at Q-value of nuclear transition
Measured quantity Half-life
Dependencies (BG limited)
T1/2 ? a ? (Mt/?EB)1/2
link to neutrino mass
1 / T1/2 PS NME2 (m? / me)2
Sum energy spectrum of both electrons
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3 Flavour oscillations (PMNS)
Analogous to CKM matrix
solar
atmospheric
If sin ?13 ? 0 ? CP-violation
U UPMNS diag(1,e i? ,e i? )
Majorana
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Physical quantities
Experimental observable Half-life
Double beta decay Effective Majorana neutrino
mass
relative CP phases ?1
Beta decay
me ? Uek2 mk
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Neutrino mass schemes and DBD
normal mass hierarchy m1ltm2ltm3
inverted mass hierarchy m3 lt m1 lt m2
almost degenerate neutrinos m1 m2 m3
quasi-degenerate
hierarchical
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Phase space
0nbb decay rate scales with Q5
2nbb decay rate scales with Q11
Q-value (keV)
(PS 0v)1 (yrs)
(PS 2v) 1 (yrs)
Isotope
Nat. abund. ()
 
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Heidelberg -Moscow

• Five Ge diodes (overall mass 10.9 kg)
• isotopically enriched ( 86) in 76Ge
• Lead box and nitrogen flushing of the detectors
• Digital Pulse Shape Analysis (factor 5
  reduction) Peak at 2039 keV

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Spectrum
0? peak region
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Evidence for 0???-decay?- References
Latest Heidelberg-Moscow results
H.V. Klapdor-Kleingrothaus et al., Eur. Phys. J.
A 12,147 (2001)
Evidence
H.V. Klapdor-Kleingrothaus et al., Mod. Phys.
Lett. A 16,2409 (2001)
Critical comments
F. Feruglio et al., hep-ph/0201291
C.A. Aalseth et al., hep-ex/0202018 and more
Reply
H.V. Klapdor-Kleingrothaus, hep-ph/0205228
H.L. Harney, hep-ph/0205293
New evidence
H.V. Klapdor-Kleingrothaus et al, Phys. Lett. B
586, 198 (2004)
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Evidence I
Statistical significance 53.93 kg x yr
Ignore det. 4 (no muon veto, slightly worse
energy resolution)
Step 1
Apply pulse shape ? 28 kg x yr
Step 2
Completely new statistical treatment - Bayesian
method
Only region of 5? around peak is used for
background determination
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Evidence II
Step 1
Step 2
Some lines known, some are not
Left hand side BG too high, hence for right hand
side onlyregion without lines except the double
beta one
For the double beta line they restrict themselves
to 5 SD region
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Heidelberg-Moscow Evidence
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Heidelberg -Moscow
more statistics Recalibration
Evidence ?
T1/2 0.6 - 8.4 x 1025 yr
m 0.17 - 0.63 eV
Subgroup of collaboration
H.V. Klapdor-Kleingrothaus et al, Phys. Lett. B
586, 198 (2004)
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If peak is real...
1.) Go out and check (GERDA, MAJORANA)
Is peak something specific to Ge?
Uncertainties in the nuclear matrix elements?
? Check with a different isotope
Physics mechanism at work ?
? Tracking
2.) NEMO, COBRA
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Running experiments
CUORICINO cryogenic bolometers40.7 kg TeO2
T1/2 gt 1.8 x 1024 yr (90 CL)
Arnaboldi et al, hep-ex/050134
NEMO-3 TPC
Future CUORE 760 kg TeO2 approved
10 kg enriched foils, 6 kg 100Mo
T1/2 gt 3.1 x 1023 yr (90 CL)
Idea Super-NEMO (100 kg)
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C0BRA
Use large amount of CdZnTe
Semiconductor Detectors
Array of 1cm3 CdTe detectors
K. Zuber, Phys. Lett. B 519,1 (2001)
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Isotopes
nat. ab. ()
Q (keV)
Decay mode
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Advantages

• Source detector

• Semiconductor (Good energy resolution, clean)

• Room temperature (safety)

• Modular design (Coincidences)

• Two isotopes at once

Industrial development of CdZnTe detectors

• 116Cd above 2.614 MeV

• Tracking (Solid state TPC)

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Cobra - The people
C. Gößling, H. Kiel, D. Münstermann, S. Oehl, T.
Villett
University of Dortmund
T. Leigertwood, D. McKechan, C. Reeve, J. Wilson,
K. Zuber
University of Sussex
P.F. Harrison, B. Morgan, Y. Ramachers, D. Stewart
University of Warwick
A. Boston, P. Booth, P. Nolan
University of Liverpool
B. Fulton, R. Wadsworth
University of York
T. Bloxham, M. Freer
University of Birmingham
P. Seller
Rutherford Appleton Laboratory
M. Junker
Laboratori Nazionali del Gran Sasso
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The 2x2 prototype

Installation of setup at Gran Sasso Underground
Laboratory
4 naked 1cm3 CdZnTe
Very preliminary
Cd113
0? region Cd116
0? region Te130
2.5 kg x days of data
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The 64 detector array
Aim for next 2 years The next step towards a
large scale experiment, Scalable modular design,
explore coincidences
Mass factor 16 higher, about 0.4 kg CdZnTe
Include CoolingNitrogen flushing

• Physics
• - Can access
• 2?ECEC in theoreticallypredicted region
• Precision measurement of 113Cd
• - New limits

Part of the detectors at Dortmund
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The solid state TPC
Introduce tracking properties by using
segmented, Pixellated electrodes and pulse shape
analysis
Single electron spectra
Angular correlation coefficient ?
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Pixellated detectors
3D - Pixelisation
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Contents

• Introduction
• Double beta decay
• COBRA
• Outlook
• Summary and conclusions

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0nbb Experimental Situation
2 main experimental approaches

• Active Source
• Passive Source

Best 0n2b results involve active source
experiments
Experiment Isotope T1/20n (y) ltmngt (eV)
You Ke et al. 1998 48Ca gt 9.5 ? 1021 (76) lt 8.3
Klapdor-Kleingrothaus 2001 76Ge gt 1.9 ? 1025 lt 0.35
Aalseth et al 2002 gt 1.57 ? 1025 lt 0.33 - 1.35
Arnold et al. 2004 82Se gt 1.3 x 1023 lt 1.5-3.1
Arnold et al. 2004 100Mo gt3.1 ? 1023 lt 0.33-0.84
Danevich et al. 2000 116Cd gt 1 ? 1023 lt 2.2
Bernatowicz et al. 1993 130/128Te (3.52 ?0.11) ? 10-4 lt 1.1 1.5
Bernatowicz et al. 1993 128Te gt 7.7 ? 1024 lt 1.1 1.5
Arnaboldi et al. 2005 130Te gt 1.8 ? 1024 lt 0.5 1.1
Luescher et al. 1998 136Xe gt 4.4 ? 1023 lt 1.8 5.2
Belli et al. 2001 136Xe gt 7 ? 1023 lt 1.4 4.1
De Silva et al. 1997 150Nd gt 1.2 ? 1021 lt 3
Danevich et al. 2001 160Gd gt 1.3 ? 1021 lt 26
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Back of the envelope
T1/2 ln2 a NA M t / N?? (t??T) (
Background free)
50 meV implies half-life measurements of 1026-27
yrs
1 event/yr you need 1026-27 source atoms

This is about 1000 moles of isotope, implying 100
kg
Now you only can loose nat. abundance,
efficiency, background, ...
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2??? - decay
2??? is ultimate, irreducible background
Energy resolution important ? semiconductor
Fraction of 2??? in 0 ??? peak
S. Elliott, P. Vogel, Ann. Rev. Nucl. Part. Sci.
2002
Signal/Background
Tracking option
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Future projects
O.Cremonesi, n 2002
Experiment Author Isotope Detector description T5y1/2(y) ltmngt
COBRA Zuber 2001 116Cd 10 kg CdTe semiconductors 1 x 1024 0.71
CUORICINO Arnaboldi et al 2001 130Te 40 kg of TeO2 bolometers 1.5 x 1025 0.19
NEMO3 Sarazin et al 2000 100Mo 10 kg of bb(0n) isotopes (7 kg Mo) with tracking 4 x 1024 0.56
CUORE Arnaboldi et al. 2001 130Te 760 kg of TeO2 bolometers 7 x 1026 0.027
EXO Danevich et al 2000 136Xe 1 t enriched Xe TPC 8 x 1026 0.052
GEM Zdesenko et al 2001 76Ge 1 t enriched Ge diodes in liquid nitrogen water shield 7 x 1027 0.018
GENIUS Klapdor-Kleingrothaus et al 2001 76Ge 1 t enriched Ge diodes in liquid nitrogen 1 x 1028 0.015
MAJORANA Aalseth et al 2002 76Ge 0.5 t enriched Ge segmented diodes 4 x 1027 0.025
DCBA Ishihara et al 2000 150Nd 20 kg enriched Nd layers with tracking 2 x 1025 0.035
CAMEO Bellini et al 2001 116Cd 1 t CdWO4 crystals in liquid scintillator gt 1026 0.069
CANDLES Kishimoto et al 48Ca several tons of CaF2 crystal in liquid scintillator 1 x 1026
GSO Danevich 2001 160Gd 2 t Gd2SiO5Ce cristal scintillator in liquid scintillator 2 x 1026 0.065
MOON Ejiri et al 2000 100Mo 34 t natural Mo sheets between plastic scintillator 1 x 1027 0.036
Xe Caccianiga et al 2001 136Xe 1.56 t of enriched Xe in liquid scintillator 5 x 1026 0.066
XMASS Moriyama et al 2001 136Xe 10 t of liquid Xe 3 x 1026 0.086
Staudt, Muto, Klapdor-Kleingrothaus Europh.
Lett 13 (1990) 31
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Future - Ge approaches
MAJORANA
500 kg of enrichedGe detectors
GERDA
Naked enriched Ge-crystals inLAr with lead shield
Segmentation and pulse shape discrimination
20 kg enriched Ge-detectorsat hand (former HD-MO
and IGEX)
MERGE
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EXO
New feature
Tracking and scintillation
136Xe ? 136Ba e- e- final state can be
identified using optical spectroscopy (M.Moe
PRC44 (1991) 931)
200 kg enriched Xe prototype under construction
at WIPP
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?? - modes
n
p
e
In general
Double charged higgs bosons, R-parity violating
SUSY couplings, leptoquarks...
e
p
n
Q-4mec2

• (A,Z) ? (A,Z-2) 2 e (2?e) ??

Q-2mec2

• e- (A,Z) ? (A,Z-2) e (2?e ) ?/EC

Q

• 2 e- (A,Z) ? (A,Z-2) (2?e) EC/EC

Important to reveal mechanism if 0??? is
discovered
Enhanced sensitivity to right handed weak
currents (VA)
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Summary
Double beta decay is the gold plated channel to
probethe fundamental character of neutrinos
Taking current evidences from oscillation data it
islikely to be the only way to fix the absolute
neutrino mass
To go below 50 meV requires hundreds of kilograms
ofenriched material
However, there is a hotly discussed evidence by
the Heidelberg group, which would imply almost
degenerate neutrinos
A lot of proposals and RD projects among them is
COBRA using CdZnTe semiconductors
We need info on nuclear matrix elements !
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