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Cobra

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0 : Only possible if neutrinos are Majorana particles. In nature there ... C. Reeve, J. Wilson, K. Zuber. University of Sussex further interested institutes ... – PowerPoint PPT presentation

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Title: Cobra


1
K. Zuber, Univ. of Sussex
Epiphany Conference Cracow, 5-7 Jan. 2006
Neutrinoless double beta decay experiments
2
Contents
  • Double beta decay
  • and neutrino masses
  • Experimental status
  • Future activities
  • Outlook and summary

3
Beta and double beta decay
Beta decay
-
  • (A,Z) ? (A,Z1) e- ?e ?-decay

-
  • n ? p e- ?e

Double beta decay
-
  • (A,Z) ? (A,Z2) 2 e- 2?e 2???
  • (A,Z) ? (A,Z2) 2 e- 0???

changing Z by two units while leaving A constant
0??? Only possible if neutrinos are Majorana
particles
In nature there are 35 isotopes
2??? Seen in 12 isotopes, important for nuclear
physics input
4
Neutrino mass schemes
almost degenerate neutrinos m1 m2 m3
hierarchical neutrino mass schemes
normal
inverted
5
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
6
Physical quantities
Experimental observable Half-life
Double beta decay Effective Majorana neutrino
mass
relative CP phases ?1
Beta decay
me ? Uek2 mk
7
Neutrino mass schemes and DBD
normal mass hierarchy m1ltm2ltm3
inverted mass hierarchy m3 lt m1 lt m2
almost degenerate neutrinos m1 m2 m3
Benchmark number to discriminate
betweenhierarchical models m 50 meV
8
?? - 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)
9
Neutrino mass vs. right handed currents
lt?gt
EC/ß
Possible evidence
ltm?gt (eV)
M. Hirsch et al., Z. Phys. A 347,151 (1994)
10
Rp violating SUSY
Double beta probes
11
Contents
  • Double beta decay
  • and neutrino masses
  • Experimental status
  • Future activities
  • Outlook and summary

12
Requirements
Weizsäcker formula for Aconst near minimum well
approximated by
Pairing energy ? leads to splitting ? 0 for
even-odd, odd-even ? - 12 MeV/A1/2 for
even-even? 12 MeV/A1/2 for odd-odd
??
There are 35 ?-?- isotopes in nature
13
Example - Ge76
14
Phase space
0nbb decay rate scales with Q5
2nbb decay rate scales with Q11
Q-value (keV)
(PS 0v)1 (yrs x eV2)
(PS 2v) 1 (yrs)
Isotope
Nat. abund. ()
 
15
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 ME2 (m? / me)2
Sum energy spectrum of both electrons
Nuclear physics input needed !
16
Nuclear matrix elements
measured quantity
quantity of interest
1 / T1/2 PS NME2 (m? / me)2
The big unknown
Started worldwide effort for a coherentprogram
to reduce NME uncertainty down to 30, summary
report available nucl-ex/0511009
Needs international coherent effort
http//www.ippp.dur.ac.uk/0NU2B/2005.html
17
Nuclear matrix elements
1 / T1/2 PS ME2 (m? / me)2
charge exchange(n,p), (d,2He)
charge exchange(p,n), (3He,t)
muon capture
nu N scattering
1
beta- decays
(A,Z1)
EC/beta decays
antineutrino-capture
0
(A,Z)
Q - values
0
(A,Z2)
Theory Shopping list what to measure to improve
calculations
Experiment Where can it be measured, who?
Follow up workshop held at Osaka, Dec. 2005 , NNR
05
18
Outcome Working packages
  • Working package 1 Charge exchange reactions
  • Working package 2 Q-value measurements
  • Working package 3 Muon capture
  • Working package 4 Double electron capture
  • Working package 5 Neutrino nucleus scattering
  • Working package 6 Nucleon transfer reaction

Urgency Some facilities might vanish in the near
future!!!
19
Double beta transitions
All even-even ground state transitions are 0 ? 0
FermisGolden rule
2???
Only Gamow-Teller transitions
20
Charge exchange reactions
2??? Only intermediate 1 states contribute
Supportive measurementsfrom accelerators
Done for Ca-48 and Cd-116 and some
other systems, all needed
Currently (d,2He) and (3He,t)
21
The dominant problem - Background
How to measure half-lives beyond 1020 years???
  • The usual suspects (U, Th nat. decay chains)
  • Alphas, Betas, Gammas
  • Cosmogenics
  • thermal neutrons

  • High energy neutrons from muon interactions
  • 2???

22
Heidelberg -Moscow
  • Five Ge Diodes (mass 10.9 kg)
  • Isotopical enriched ( 86) in 76Ge
  • lead shield and nitrogen purging Peak at
    2039 keV

H.V. Klapdor-Kleingrothaus et al, Europ. Phys. J.
A 12, 147 (2001)
T1/2 gt 1.9 x 1025 yr (90 CL)
m lt 0.35 eV
Evidence ?
Subgroup of collaboration
T1/2 0.6 - 8.4 x 1025 yr
m 0.17 - 0.63 eV
H.V. Klapdor-Kleingrothaus et al, Phys. Lett. B
586, 198 (2004)
23
CUORICINO/CUORE - Principle
Thermal coupling
example 750 g of TeO2 _at_ 10 mKC T 3 (Debye) ?
C 2 x10-9 J/K1 MeV g-ray ? DT 80 mK ? DU
10 eV
24
CUORICINO - Results
about 40 kg running
208Tl
60Co sum
130Te DBD
T1/2 gt 1.8 x 1024 yrs (90 CL) m lt 0.2-1.1 eV
C.Arnaboldi et al, hep-ex0501034, Phys. Rev.
Lett. 2005
Idea CUORE (750 kg) approved by INFN
25
NEMO-III
Only approach with source different from detector
100Mo 6.914 kg Qbb 3034 keV
82Se 0.932 kg Qbb 2995 keV
26
100Mo results
7.37 kg.y
(Data Feb. 2003 Dec. 2004)
Angular Distribution
Sum Energy Spectrum
219 000 events 6914 g 389 days S/B 40
219 000 events 6914 g 389 days S/B 40
NEMO-3
NEMO-3
100Mo
100Mo
E1 E2 (keV)
Cos(?)
2???
T1/2 7.14 0.02 (stat) 0.54 (syst) ? 1018 y
0???
T1/2 gt 3.1 x 1023 yrs (90 CL)
m? lt 0.7 - 2.8 eV
Idea Super-NEMO (100 kg)
R. Arnold et al, hep-ex/0507083
27
COBRA
Use large amount of CdZnTe
Semiconductor Detectors
Array of 1cm3 CdTe detectors
K. Zuber, Phys. Lett. B 519,1 (2001)
28
Cobra - The people
further interested institutes
D. Dobos, C. Gößling, H. Kiel, D. Münstermann, S.
Oehl, T. Villett
University of Dortmund
J. Dawson, C. Montag, D. Palzaird, C.
Reeve, J. Wilson, K. Zuber
University of Sussex
P.F. Harrison, B. Morgan, Y. Ramachers, D. Stewart
University of Warwick
A. Boston, P. Nolan
University of Liverpool
S. Fox, B. Fulton, A. Smith, R. Wadsworth
University of York
T. Bloxham, M. Freer
University of Birmingham
P. Seller
Rutherford Appleton Laboratory
M. Junker
Laboratori Nazionali del Gran Sasso
29
Isotopes
nat. ab. ()
Q (keV)
Decay mode
30
Advantages
  • Source detector
  • Semiconductor (Good energy resolution, clean)
  • Room temperature (safety)
  • Modular design (Coincidences)
  • Two isotopes at once

Industrial development of CdTe detectors
  • 116Cd above 2.614 MeV
  • Tracking (Solid state TPC)

31
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
32
The 2x2 prototype

Setup installed at Gran Sasso Underground
Laboratory
4 naked 1cm3 CdZnTe
more than 3.8 kg x days of data
33
Physics - 113Cd
113Cd one of only three 4-fold forbidden
?-emitters known in nature
T1/2 (8.2 0.2 (stat.) 0.2-1.0 (sys)) 1015 yrs
C. Goessling et al., nucl-ex/0508016, acc. by
Phys. Rev. C
34
First results
H.Kiel, D. Münstermann, K. Zuber, Nucl. Phys. A
723,499 (2003)
0???
NPA 723
COBRA
EC-modes
COBRA
NPA723
T1/2 close to 1020 years obtained
Current results are preliminary
64Zn limits world best
35
Coincidences
Aim Coincidences among crystals should
significantly reduce gamma background
2614 keV gamma (MC)
About 0.2 ofevents are coincidences
Array too small to prove power of coincidences ?
Larger Array
36
The 64 detector array
Aim for next 2 years The next step towards a
large scale experiment, Scalable modular design,
explore coincidences
Mass is factor 16 higher, about 0.5 kg CdZnTe
Include CoolingNitrogen flushing
  • Physics
  • - Can access
  • 2?ECEC in theoreticallypredicted region
  • Precision measurement of 113Cd
  • - New limits

Detectors are at Dortmund, LNGS spring 06
37
The solid state TPC
Introduce tracking properties by using
segmented or pixellated electrodes and pulse
shape analysis
Single electron spectra
Angular correlation coefficient ?
38
Pixellated detectors
Solid state TPC
3D - Pixelisation
39
Nobody said it was going to be easy, and nobody
was right
George W. Bush
40
Join the Party!
41
Contents
  • Double beta decay
  • and neutrino masses
  • Experimental status
  • Future activities
  • Outlook and summary

42
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, ...
43
Future projects
small scale ones will expand, very likely not a
complete list...
44
Dimension it right!
Current idea 40x40x40 CdZnTe detectors 420 kg,
enriched in 116Cd
45
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
46
?L2 Processes
In general 9 mass terms
?e-conversion on nuclei

M. Flanz, W. Rodejohann, K. Zuber, Eur. Phys. J.
C 16, 453 (2001)
W. Rodejohann, K. Zuber,Phys. Rev. D 63, 054031
(2001)

limits on ltm??gt (in GeV)
K. Zuber, Phys. Lett. B 479,33 (2000)

M. Flanz, W. Rodejohann, K. Zuber,Phys. Lett. B
473, 324 (2000)
W. Rodejohann, K. Zuber,Phys. Rev. D 62, 094017
(2000)
Limits are unphysical
47
Candidate events
NOMAD trimuon event
H1 charged current event
48
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 disputed evidence by
the Heidelberg group, which would imply almost
degenerate neutrinos
To account for matrix element uncertainties
supportivemeasurements are considered and in
addition todisentangle the physics mechanism we
need at least 3(4) isotopes measured
49
Hope....
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