1. Double beta decay and Majorana neutrinos
Ettore Fiorini, Venice March 8, 2007
→ → <= =>
Majorana =>1937
Presently an essential problem in neutrino and in astroparticle physiss

2. The most sensitive way to investigate the Dirac or Majorana nature of the neutrino is neutrinoless double beta decay (DBD) This very rare process was sugested in general form by Maria Goepper Mayer just one year after the Fermi theory of beta decay. Also Bruno Pontecorvo was deeply involved.

3. Double Beta –Disintegration M
Double Beta –Disintegration M.Goeppert-Mayer, The John Hopkins University (Received May, 20 , 1935) From the Fermi theory of b- disintegration the probability of simultameous emission of two electrons (and two neutrinos) has been calculated. The result is that this process occurs sufficiently rarely to allow an half-life of over years for a nucleus, even if its isobar of atomic number different by 2 were more stable by 20 times the electron mass
Double beta decay was at the beginning searched In the neutrinoless channel as a powerful way to search for lepton number non conservation. Presently it is also considered as the most powerful way to investigate the value of the mass of a Majorana neutrino

4. 1. (A,Z) => (A,Z+2) + 2 e- + 2 ne¯ 2
1. (A,Z) => (A,Z+2) + 2 e ne¯ 2. (A,Z) => (A,Z+2) + 2 e- + c ( …2,3 c) 3. (A,Z) => (A,Z+2) + 2 e-
Process 1 has been detected in ten nuclei
Process2 and 3. violate the lepton number
Process 3, normally called neutrinoless DBD, would be revealed by
the presence of a peak in the sum of the electron energies => <mn>≠ 0

5. Neutrinoless bb decay 0n - bb decay 2n - bb decay u e - d W n e - d u

6. 1/t = G(Q,Z) |Mnucl|2 <mn>2
The rate of neutrinoless DBD strongly depends on the evaluation of the nuclear matrix elements, quite uncertain so far
1/t = G(Q,Z) |Mnucl|2 <mn>2
rate of DDB-0n
Phase space
Nuclear matrix
elements
EffectiveMajorana
neutrino mass
Need to search for neutrinoless DBD in various nuclei A pick could be due to some unforeseen background peak

9. Possible schemes for neutrino masses

10. New calculations by.S.Pascoli and S.T.Petkov

11. Experimental approaches Source = detector (calorimetric)
Geochemical experiments i82Se = > 82Kr, 96Zr = > 96Mo (?) , 128Te = > 128Xe (non confirmed), 130Te = > 130Te Radiochemical experiments 238U = > 238Pu (non confirmed) e-
Direct experiments
Source = detector (calorimetric)
Source  detector e-
source
detector
Source  Detector

13. Cryogenic detectors heat bath Thermal sensor absorber crystal
Incident particle
absorber
crystal

14. @ 2 MeV ~10 mk ~ 1 kg <10 eV ~ keVDE
@ 5 keV ~100 mk ~ 1 mg <1 eV ~ 3 eV
@ 2 MeV ~10 mk ~ 1 kg <10 eV ~ keV

15. Resolution of the 5x5x5 cm3 (~ 760 g ) crystals
Energy [keV]
Counts
210Po a line :
0.8 keV FWHM @ 46 keV
1.4 keV FWHM @ MeV
2.1 keV FWHM @ MeV
2.6 keV FWHM @ MeV
3.2 keV FWHM @ MeV
(the best a spectrometer ever realized)

16. Present experimental situation
Nucleus
Experiment %
Qbb
Enr
Technique
T0n (y)
<mn)
48Ca
Elegant IV
0.19
4271
scintillator
>1.4x1022
7-45
76Ge
Heidelberg-Moscow
7.8
2039 87
ionization
>1.9x1025
IGEX
Ionization
>1.6x1025
.14 – 1.2
Klapdor et al
1.2x1025
.44
82Se
NEMO 3
9.2
2995 97
tracking
>1.x1023
100Mo
9.6
3034
95-99
>4.6x1023
.7-2.8
116Cd
Solotvina
7.5 83
>1.7x1023
1.7 - ?
128Te
Bernatovitz 34
2529
geochem
>7.7  1024
.1-4
130Te
Cuoricino
33.8
bolometric
>2x1024
136Xe
DAMA
8.9
2476 69
>1.2x1024
150Nd
Irvine
5.6
3367 91
>1.2x1021
3 - ?

17. HM collaboration subset (KDHK): claim of evidence of 0n-DBD
In December 2001, 4 authors (KDHK) of the HM collaboration announce the
discovery of neutrinoless DBD
t1/20n (y) = (0.8 – 18.3)  1025 y (1  1025 y b.v.)
Mbb = eV (95% c.l.)
54.98 kg•y s
2001
71.7 kg•y s
2004
skepticism in DBD community in 2001
better results in 2004

18. Two new experiments NEMO III and CUORICINO

19.  decay isotopes in NEMO-3 detector
bb2n measurement
116Cd g
Qbb = keV
96Zr g
Qbb = 3350 keV
150Nd g
Qbb = keV
48Ca g
Qbb = 4272 keV
130Te g
Qbb = 2529 keV
External bkg
measurement
100Mo kg
Qbb = 3034 keV
82Se kg
Qbb = 2995 keV
natTe g
Cu g
bb0n search

20. 0n analysis
100Mo  t1/20n (y) > 4.6  Mbb < 0.7 – 2.8 eV (90% c.l.)
82Se  t1/20n (y) > 1.0  Mbb < 1.7 – 4.9 eV (90% c.l.)

21. CUORICINO

23. 18 crystals 3x3x6 cm3 + 44 crystals 5x5x5 cm3 = 40.7 kg of TeO2
Search for the 2b|on in 130Te (Q=2529 keV) and other rare events
At Hall A in the Laboratori Nazionali del Gran Sasso (LNGS)
18 crystals 3x3x6 cm crystals 5x5x5 cm3 = 40.7 kg of TeO2
Operation started in the beginning of 2003 => ~ 4 months
Background .18±.01 c /kev/ kg/ a
2 modules, 9 detector each,
crystal dimension 3x3x6 cm3
crystal mass 330 g
9 x 2 x 0.33 = 5.94 kg of TeO2
11 modules, 4 detector each,
crystal dimension 5x5x5 cm3
crystal mass 790 g
4 x 11 x 0.79 = kg of TeO2

25. Present CUORICINO result (new)
60Co pile-up
peak
130Te DBD
Q-value
anticoincidence spectrum
208Tl line
Energy [keV]
detail
DBD
MT = 5.87 (kg 130Te) x y
b = 0.18  0.02 c/keV/kg/y
(Jul 2005)
8.35 kg year of 130Te
t >3 x 1024 (90 % c.l.)
<m0n> < eV =>
Klapdor et al m0n < eV

26. DBD and Neutrino Masses
Present Cuoricino region
Arnaboldi et al., submitted to PRL, hep-ex/ (2005).
Possible evidence (best value eV)
H.V. Klapdor-Kleingrothaus et al., Nucl.Instrum.and
Meth. ,522, 367 (2004).
With the same matrix elements the
Cuoricino limit is 0.53 eV
“quasi” degeneracy
m1 m2  m3
Inverse hierarchy
m212= m2atm
Direct hierarchy
m212= m2sol
Cosmological disfavoured
region
(WMAP)
Feruglio F. , Strumia A. , Vissani F. hep-ph/

27. Next generation experiments
Name %
Qbb
% E B
c/y
T (year)
Tech
<m>
CUORE
130Te 34
2533 90
3.5
1.8x1027
Bolometric
9-57
GERDA
76Ge
7.8
2039
3.85
2x1027
Ionization
29-94
Majorana .6
4x1027
21-67
GENIUS .4
1x1028
13-42
Supernemo
82Se
8.7
2995 1
21026
Tracking
54-167
EXO
136Xe
8.9
2476 65
.55
1.3x1028
12-31
Moon-3
100Mo
9.6
3034 85
3.8
1.7x1027
13-48
DCBA-2
150Nd
5.6
3367 80
1x1026
16-22
Candles
48Ca
.19
4271 -
.35
3x1027
Scintillation
29-54
CARVEL
50-94
GSO
160Gd 22
1730
200
65-?
COBRA
115Cd
7.5
2805
SNOLAB+

28. Ionization

29. Ionization
COBRA

30. C0BRA Use large amount of CdZnTe Semiconductor Detectors Array of 1cm3
CdTe detectors
K. Zuber, Phys. Lett. B 519,1 (2001)

31. Nd dissolved in SNO => tons of material;
Scintillation
0n: 1000 events per
year with 1% natural
Nd-loaded liquid
scintillator in SNO++
by Alex Wright
simulation:
one year of data
maximum likelihood statistical test of the shape to extract
0n and 2n components…~240 units of Dc2 significance after only 1 year!

32. Scintillation

33. Tracking SUPERNEMO

36. Tracking

37. EXO
concept: scale Gotthard experiment adding Ba tagging to suppress background (136Xe136Ba+2e)
single Ba detected by optical spectroscopy
two options with 63% enriched Xe
High pressure Xe TPC
LXe TPC + scintillation
calorimetry + tracking
expected bkg only by -2
energy resolution E = 2%
Present R&D
Ba+ spectroscopy in HP Xe / Ba+ extr.
energy resolution in LXe (ion.+scint.)
Prototype scale:
200 kg enriched L136Xe without tagging
all EXO functionality except Ba id
operate in WIPP for ~two years
Protorype goals:
Test all technical aspects of EXO
(except Ba id)
Measure 2n mode
Set decent limit for 0n mode
(probe Heidelberg- Moscow)
2P1/2
4D3/2
2S1/2
493 nm
650 nm
metastable
47s
LXe TPC
Full scale experiment at WIPP or SNOLAB
10 t (for LXe ⇒ 3 m3)
b = 4×10-3 c/keV/ton/y
1/2  1.3×1028 y in 5 years
〈m〉  ÷ eV

43. CUORE expected sensitivity
disfavoured by cosmology
In 5 years:
Strumia A. and Vissani F. hep-ph/

44. Other possible candidates for neutrinoless DBD
Compound
Isotopic abundance
Transition energy
48CaF2
.0187 %
keV
76Ge
"
"
100MoPbO4
"
"
116CdWO4
"
"
130TeO2
"
"
150NdF NdGaO3
" “
130Te has high transition energy and 34% isotopic abundance => enrichment
non needed and/or very cheap. Any future extensions are possible
Performance of CUORE, amply tested with CUORICINO

45. How deep should we go?

46. Total Muon Flux v.s. Depth Relative to Flat Overburden (cm-2 s-1)
Depth (km.w.e) Relative to Flat Overburden

47. Neutron Flux at Underground Sites

48. eg. Study for 60 kg Majorana Module

50. CONCLUSIONS
Neutrino oscillations  Dm2 ≠0  <mn> finite for at leaqst one neutrino
Neutrinoless double beta decay would indicate if neutrino is a lepton violating Majorana particle and would allow in this case to determine <mn> and the hierachy of oscillations.
This process has been indicated by an experiment (Klapdor) with a value of ~0.44 eV but has not yet confirmed
Future experiments on neutrinoless double beta decay will allow to reach the sensitivity predicted by oscillations
The multidisciplinarity of searches on double beta decay involves nuclear and e subnuclear physics, astrophysics , radioactivity, material science, geochronology etc. It could help in explaining the particle-antiparticle asymmetry of the Universe