Transcript Cobra

K. Zuber, Univ. of Sussex
Epiphany Conference
Cracow, 5-7 Jan. 2006
Neutrinoless double beta
decay experiments
Contents
• Double beta decay
and neutrino masses
• Experimental status
• Future activities
• Outlook and
summary
Beta and double beta decay
Beta decay
• (A,Z)  (A,Z+1) + e
-e
• n  p + e- + 
-
+
e
-decay
Double beta decay
• (A,Z)  (A,Z+2) +2 e- + 2-e
• (A,Z)  (A,Z+2) + 2 e-
2
0
changing Z by two units while leaving A constant
Neutrino mass schemes
• almost degenerate neutrinos m1≈ m2≈ m3
• hierarchical
neutrino
mass schemes
normal
inverted
3 Flavour oscillations (PMNS)
Analogous to CKM matrix
  e   U e1
  
      U 1
   U
    1
U e2
U2
U 2
cos12 sin 12 0  cos13

 
U  sin 12 cos12 0 
0

 
i
0
0
1

 sin 13e
solar
U e3   1 
 e 
2
 
 
mi

U3   2  
   

2E 


 
U  3    3 
 
0 sin 13ei 1
0
0 1 0


i 1
1
0
0
cos

sin

0
e
23
23 





0 cos13 0 sin  23 cos 23 0 0
If sin 13  0  CP-violation atmospheric
Majorana: U= UPMNS diag(1,e i ,e i )
0 

0 

e i 2 
Physical quantities
Experimental observable: Half-life
Double beta decay: Effective Majorana neutrino mass
m  mee 
U
k
2
ek
mk 
U
2 i
ek
ek
e
mk
k
relative CP phases = 1
Beta decay
me =  |Uek|2 mk
Neutrino mass schemes and DBD
„normal“ mass hierarchy m1<m2<m3
„inverted“ mass hierarchy m3 < m1 < m2
almost degenerate neutrinos m1≈ m2≈ m3
Benchmark number to
discriminate between
hierarchical models:
m = 50 meV
++ - modes
n
p
e
In general:
Double charged higgs bosons,
R-parity violating SUSY couplings,
leptoquarks...
n
• (A,Z)  (A,Z-2) + 2 e+ (+2e)
p
e
++ Q-4mec2
• e- + (A,Z)  (A,Z-2) + e+ (+2e ) +/EC Q-2mec2
• 2 e- + (A,Z)  (A,Z-2) (+2e)
EC/EC Q
Important to reveal mechanism if 0 is discovered
Enhanced sensitivity to right handed weak currents (V+A)
Neutrino mass vs. right handed currents
H int  jL J L  jL J R  jR J L  jR J R
<>
EC/ß+

,  1
Possible
evidence
<m> (eV)
M. Hirsch et al., Z. Phys. A 347,151 (1994)
Rp violating SUSY
Double beta probes

111
Contents
• Double beta decay
and neutrino masses
• Experimental status
• Future activities
• Outlook and
summary
Requirements
Weizsäcker formula for A=const near minimum well approximated by
(A /2  Z) 2
Z2
m(Z, A)  const  2bS
 bC 1/ 3  me Z  
2
A
A
m
E-E
O-O
A Even
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



Zo



Z
There are 35 -- isotopes in nature
Example - Ge76
Phase space
0decay rate scales with Q5
Isotope
Ca 48
Ge 76
Se 82
Zr 96
Mo 100
Pd 110
Cd 116
Sn 124
Te 130
Xe 136
Nd 150
2 decay rate scales with Q11
Q-value Nat. abund. (PS 0v)–1
(PS 2v) –1
(keV)
(yrs x eV2)
(yrs)
(%)
4271
2039
2995
3350
3034
2013
2802
2288
2529
2479
3367
0.187
7.8
9.2
2.8
9.6
11.8
7.5
5.64
34.5
8.9
5.6
4.10E24
4.09E25
9.27E24
4.46E24
5.70E24
1.86E25
5.28E24
9.48E24
5.89E24
5.52E24
1.25E24
2.52E16
7.66E18
2.30E17
5.19E16
1.06E17
2.51E18
1.25E17
5.93E17
2.08E17
2.07E17
8.41E15
Spectral shapes
0: Peak at Q-value of nuclear transition
Measured quantity: Half-life
Dependencies (BG limited)
T1/2  a •  (M•t/E•B)1/2
link to neutrino mass
1 / T1/2 = PS * ME2 * (m / me)2
Sum energy spectrum of both electrons
Nuclear physics
input needed !
Nuclear matrix elements
measured quantity
quantity of interest
1 / T1/2 = PS * NME2 * (m / me)2
The big unknown
Started worldwide effort for a coherent
program 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
Nuclear matrix elements
1 / T1/2 = PS * ME2 * (m / me)2
charge exchange
(p,n), (3He,t)
nu N scattering
EC/beta+ decays
0+
(A,Z)
(A,Z+1)
Q - values
1+
charge exchange
(n,p), (d,2He)
muon capture
beta- decays
antineutrinocapture
(A,Z+2)
0+
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
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!!!
Double beta transitions
All even-even ground state transitions are 0+  0+
2:
d  2(E 0   E f ) 
f
m,

 f H m  m H i 
E i  E m  p  E e
2
Fermi‘s
Golden rule

Only Gamow-Teller transitions
Charge exchange reactions
2: Only intermediate 1+ states contribute
Supportive measurements
from accelerators
Done for Ca-48 and
Cd-116 and some other
systems, all needed
Currently: (d,2He) and (3He,t)
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
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 > 1.9 x 1025 yr (90% CL)
Evidence ?
m < 0.35 eV
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)
CUORICINO/CUORE - Principle
Heat sink
Thermal coupling
Thermometer
Double beta decay
Crystal absorber
example: 750 g of TeO2 @ 10 mK
C ~ T 3 (Debye)  C ~ 2 x10-9 J/K
1 MeV g-ray
 T ~ 80 K
 U ~10 eV
CUORICINO - Results
about 40 kg running
60Co
208Tl
sum
130Te
DBD
T1/2 > 1.8 x 1024 yrs
(90% CL)
m < 0.2-1.1 eV
C.Arnaboldi et al, hep-ex0501034,
Phys. Rev. Lett. 2005
Idea:
CUORE (750 kg)
approved by INFN
NEMO-III
Only approach with source different from detector
100Mo
6.914 kg
Q= 3034 keV
82Se
0.932 kg
Q= 2995 keV
100Mo
results
7.37 kg.y
(Data Feb. 2003 – Dec. 2004)
Sum Energy Spectrum
NEMO-3
100Mo
219 000 events
6914 g
389 days
S/B = 40
•
Data
22
Monte Carlo
Background
subtracted
Angular Distribution
219 000 events
6914 g
389 days
S/B = 40
NEMO-3
100Mo
•
Data
22
Monte Carlo
Background
subtracted
E1 + E2 (keV)
Cos()
2:
0: T1/2
T1/2 = 7.14  0.02 (stat)  0.54 (syst)  1018 y
m < 0.7 - 2.8 eV
> 3.1 x 1023 yrs (90% CL)
R. Arnold et al, hep-ex/0507083
Idea: Super-NEMO (100 kg)
COBRA
Use large amount of
CdZnTe
Semiconductor Detectors
Array of 1cm3
CdTe detectors
K. Zuber, Phys. Lett. B 519,1 (2001)
+ further interested institutes
Cobra - The people
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
Isotopes
nat. ab. (%) Q (keV)
Zn70
Cd114
Cd116
Te128
Te130
Zn64
Cd106
Cd108
Te120
0.62
28.7
7.5
31.7
33.8
48.6
1.21
0.9
0.1
1001
534
2809
868
2529
1096
2771
231
1722
Decay mode
ß-ßß-ßß-ßß-ßß-ßß+/EC
ß+ß+
EC/EC
ß+/EC
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“)
2 - decay
2 is ultimate, irreducible background
Energy resolution important  semiconductor
8Q(E /Q) 6
10
F


3.7
*10
Fraction of 2 in 0  peak:
me
S. Elliott, P. Vogel, Ann. Rev. Nucl. Part. Sci. 2002
Signal/Background:

S 1 T12/ 2

 433
0
B F T1/ 2
T12/ 2  3.2 1019 yrs
T10/2  21026 yrs
+ Tracking option
The 2x2 prototype
Setup installed at Gran Sasso Underground Laboratory
4 naked 1cm3 CdZnTe
more than 3.8 kg x days of data
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
First results
H.Kiel, D. Münstermann, K. Zuber, Nucl. Phys. A 723,499 (2003)
0
T1/2 close to
years obtained
1020
NPA 723 COBRA
70Zn
1.3 x 1016
2.7x1017
116Cd
8.0 x1018
1.2x1019
130Te
3.3x1019
5.7x1019
EC-modes
NPA723
106Cd
0+
EC
3.8x1017
2.5 x1019
64Zn
0+
EC
2.8x1016
5.1x1018
64Zn
0ECEC 2.2x1016
9.6x1016
COBRA
Current results are preliminary
64Zn
limits world best
Coincidences
Aim: Coincidences among crystals should significantly reduce
gamma background
2614 keV gamma (MC)
2000keV
1
30
0.9
25
0.8
0.7
20
0.6
y
0.5
15
0.4
10
About 0.2 % of
events are
coincidences
0.3
0.2
5
0.1
5
10
15
x
20
25
30
0
Array too small to prove power of coincidences  Larger Array
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
Detectors are at Dortmund, LNGS spring 06
Include:
Cooling
Nitrogen flushing
Physics:
- Can access
2ECEC in theoretically
predicted region
-Precision measurement
of 113Cd
- New limits
The solid state TPC
Introduce tracking properties by using segmented
or pixellated electrodes and pulse shape analysis
Single electron spectra
Angular correlation
coefficient 
Pixellated detectors
Solid state TPC
3D - Pixelisation:
Nobody said it was going to be easy, and nobody was right
George W. Bush
Contents
• Double beta decay
and neutrino masses
• Experimental status
• Future activities
• Outlook and
summary
Back of the envelope
T1/2 = ln2 • a • NA• M • t / N (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, ...
Future projects
small scale ones will expand, very likely not a complete list...
Dimension it right!
Current idea: 40x40x40 CdZnTe detectors = 420 kg, enriched in 116Cd
Sensitivity
50 meV
EXO
Tracking and scintillation
New feature:
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
L=2 Processes
In general 9 mass terms
•
e-conversion on nuclei
m 
UkU k mk 
CP
U
U
m

 k k k k
k
k
  
•  N     X
M. Flanz, W. Rodejohann, K. Zuber,
Eur. Phys. J. C 16, 453 (2001)
W. Rodejohann, K. Zuber,
Phys. Rev. D 63, 054031 (2001)
• K      
K. Zuber, Phys. Lett. B 479,33 (2000)
•
e p  ve   (  )  (  ) X
M. Flanz, W. Rodejohann, K. Zuber,
Phys. Lett. B 473, 324 (2000)
W. Rodejohann, K. Zuber,
Phys. Rev. D 62, 094017 (2000)
limits on <m> (in GeV)
3.5 10-10
1.7 (8.2) 10-2
8.4 103
500
8.7 103
2.0 104
Limits are unphysical
Candidate events
H1 charged current event
NOMAD trimuon event
e p  ve   (  )  (  ) X
  N      X
Summary
Double beta decay is the gold plated channel to probe
the fundamental character of neutrinos
Taking current evidences from oscillation data it is
likely to be the only way to fix the absolute neutrino mass
To go below 50 meV requires hundreds of kilograms of
enriched material
However, there is a hotly disputed evidence by the
Heidelberg group, which would imply almost degenerate
neutrinos
To account for matrix element uncertainties supportive
measurements are considered and in addition to
disentangle the physics mechanism we need at least 3(4)
isotopes measured
Hope....