1. CUTAPP05
A. Caldwell/MPI

2. I assume you all know about 0-DBD
I assume you all know about 0-DBD. We have not found a better way to test whether the neutrino is a Majorana particle. Will focus on particulars of our effort (GERDA).
Topics covered:
Selected review
Why we chose Germanium
Where we hope to improve over previous experiments
Importance of background reduction
Current status of GERDA

3. Decay rate, nuclear matrix elements
If resolution poor
Normalized energy spectrum
If resolution good
Nuclear matrix element
Effective Majorana mass
Phase
space
 Q5
0-DBD
rate
1/t = G(Q,Z) |Mnucl|2 mee2

4. Decay rate - cont.  = (G(Q,Z) |Mnucl|2 mee2)-1 fix mee=50 meV
X 1026 years
reserve
About factor 10 range in lifetime due to nuclear matrix elements – factor three for mee limits. Actual uncertainty  ?
 Demonstrate Majorana nature. Mass determination ?

5. What previous experiments teach us
It’s all about background, background, background
How big is it ?
What is the source ?
And also a bit about E
resol.
Counts/keV/kg/day

6. Backgrounds - statistical analysis
The discovery potential depends strongly on the background level ! Here is a Bayesian analysis assuming a flat prior for the rate ( /yr). Discovery is defined by requiring that the probability that R=0 is less than
Just for illustration
Background rate /kg/yr
H-M Background
K-K et al.
Cuoricino

7. Heidelberg-Moscow Background: 0.11/keV/kg/yr 0 DBD signal ??
H.V. Klapdor-Kleingrothaus, I.V. Krivosheina, A. Dietz, O. Chkvorets (Heidelberg, Max Planck Inst.)
Phys.Lett.B586: ,2004
Background: 0.11/keV/kg/yr
0 DBD signal ??
reserve
Known Bi lines
With pulse shape analysis

8. Heidelberg-Moscow
A 4.2 signal
T1/2= yr

9. Background model in HD-Moscow (diploma thesis Christian Dörr, 2002)
simulate Ge and shielding (Geant 4 + nuclear decays + gg correlations)
goal: describe the measured background spectrum to extract 2 signal
Comparison signal data/MC
Comparison data/MC for Th calibration source
Red=simulation Black = data
[keV]
[keV]
reserve
[keV]
result: no indication for background in Ge detector (after 5y), mainly in Cu cryostat, less in Pb
[keV]

10. IGEX/Majorana Experiment
Heidelberg-Moscow collaboration has insisted that external backgrounds are the main worry. Drives design decision for GENIUS, GERDA. IGEX  Majorana collaboration has stressed that eventual limit will come from radioactivity internal to Ge crystals.
Cosmogenic activity was the limiting factor in IGEX (68Ge and 60Co)
build detectors underground
shielding uses old lead, Cu (need very low activity)
pulse shape discrimination
detector segmentation

11. Cuoricino Total mass ~41 kg 11 modules 4 detector each,
5x5x5 cm3 790 g TeO2 crystals
2 modules 9 detector each,
3x3x6 cm3 330 g TeO2 crystals +

12. Total Statistics: 10.85 kgxy
arXiv:hep-ex/ v1
Background
0.18 ± 0.01 c/keV/kg/y
DBD0 result:
T1/2130Te
<m> < [0.2÷1.1] eV
> 1.8 x 1024 y
reserve

13. NEMO3 Source in form of foils: 1 SOURCE
reserve
1 SOURCE
2 TRACKING VOLUME
3 CALORIMETER
Tracking volume with Geiger cells
e+/e- separation by magnetic field
Plastic scintillators for calorimetry and timing

14. NEMO3: first results Signal region
First results on 100Mo (650 h) 2n
spectrum
Signal region
reserve
t1/22n (y) = 7.8 ± 0.09 stat ± 0.8 syst  y
t1/20n (y) > 6  y
Very small background, but small mass & poor energy resolution
These data should be very valuable in tuning the nuclear models

15. Proposed experiments Some of the possible isotopes
48Ca g 48Ti Qbb = 4271 keV nat. abund. = 0.2%
76Ge g76Se Qbb = 2039 keV nat. abund. = 7.4%
82Se g 82Kr Qbb = 2995 keV nat. abund. = 8.4%
96Zr g 96Mo Qbb = 3350 keV
100Mo g100Ru Qbb = 3034 keV nat. abund. = 9.6%
116Cd g116Sn Qbb = 2802 keV
128Te g128Xe Qbb = keV
130Te g130Xe Qbb = 2529 keV nat. abund. = 34%
136Xe g136Ba Qbb = 2479 keV nat. abund. = 8.9%
150Nd g150Sm Qbb = 3367 keV nat. abund. = 5.6%

16. Why Germanium Germanium is a good choice because:
excellent energy resolution (0.1% at 2MeV). Allows finer binning, so less background. There is always the irreducible background from allowed 2 mode which can only be distinguished via energy resolution.
considerable experience worldwide-Heidelberg Moscow, IGEX, Majorana. Some hope that we know background sources & can reduce it.
enrichment possible (but expensive)
possibilities for further development (segmentation)

17. Q=2.039 MeV
If DBD generated ONLY by (V-A) charged current weak interaction via the exchange of three (light) Majorana neutrinos, the decay amplitude factorizes in the effective majorana mass m_ee

18. Engineer’s conception
External backgrounds
Artist’s conception
Engineer’s conception
Suppress 208Tl MeV , n, 
Reduce external backgrounds to 10-3/keV/kg/yr

19. Internal Backgrounds
cosmogenic production in 76Ge at sea level: about 1 68Ge / (kg day)
(Majorana white book, simulation + measurement). Considering experiments to measure cosmogenic activation.
MeV
From B. Swchingenheuer MPI-K
Dominant decay chain:
68Ge  68Ga via EC (10.6 KeV )
=271 days
68Ga  68Zn via + (90%, 1.9 MeV)
+  (0.511 MeV)
=68 minutes
Possibility to distinguish 2.0 MeV  + (s) from 2x1.0 MeV - ?
reserve

20. Internal Backgrounds
60Co after 10 days of activation and 3 years of storage mBq/kg  5.4 decays/(kg y)
MeV
Dominant decay chain:
60Co  60Ni via
- (0.316 MeV)
+  (1.17 MeV)
+  (1.33 MeV)
= 5.27 years
Possibility to distinguish gammas from electron ?
reserve
+other stuff: surface contamination, supports and cables, …

21. Pulse shape, segmentation
Can we distinguish single versus multiple energy deposits ? Tools: pulse timing, segmentation.
Photon attenuation
R=1/x = 4 cm for 1 MeV 
Range of electrons in Germanium (from NIST tables)
68Ga +
76Ge -
reserve

22. Developments for GERDA
Water tank, Cryo tank, clean room, superstructure designs
Testing & refurbishments of existing detectors - Phase I of GERDA
Procurement of new detectors for Phase II
Simulation studies

23. Infrastructures in HALL A: Super-Structure & Water tank

24. Infrastructures in Hall A: Super-insulated cryogenic vessel
Two design studies for Cu-cryostat available:
Steel-cryostat:
with optimized shielding
Cu-cryostat:
hanging from neck
Cu-cryostat:
resting on pads
Cu-cryostat purchase process commenced with publication in ’Supplememnt of the Official Journal of the European Union’ a ’Prior Information Notice’ - SIMAP-MPI-K 31 Jan’05 ID: ; 7 companies expressed interest
Decision taking Cu vs. steel cryostat: Cu-Steel welding tests and certification

25. Infrastructure in Hall A: Cryogenic systems for (re-)filling and cooling
Cryogenmash design
Sommer design

26. Testing and modification of enriched detectors
November, 2004, in LENS barrack
(prior to barrack refurbishment)
Energy resolution at MeV
ANG1
ANG2
ANG3
ANG4
ANG5
HdMo
Setup
3.0
3.4
3.5
GERDA
Lab, Jan.05
3.9
2.7
2.8
3.1
Notes
Warm Up
PA gain ‘jumps’
Co-60 source - absolute efficiency (done)
Ba-133 source - dead layer thickness estimation (done)
Check of ANG2 (ongoing)

27. Modification of enriched detectors
Design study for a Cu/Si/PTFE-only
detector support/contact system
Minimizing mass vs. strength
(current design: factor 5 safety)
Alternative: Silicon support

29. New detectors for Phase II: Procurement of enriched Ge
Ge procurement is done in two steps:
procurement of 15 kg of natural Ge (‘test run’)
subsequently procurement of kg of 76Ge (‘real run’)
Both samples produced in Siberia / Russian Federation
15 kg ‘test run’ (6N) Ge shipped in same way as enriched sample.
Specially designed protective steel container (PSC) which reduces activation by cosmic rays by factor 20 is used for transportation
Procurement of natural Ge successfully concluded; sample received at MPI Munich on March 7, 2005

30. MaGe simulations of muon induced backgrounds (GSTR-05-003)
Implementation of
Underground  energy spectrum
 angular distribution
Full detector geometry
Energy (GeV) 
cos

31. MaGe: MC for Gerda & Majorana
3x7 Ge crystals
Electronic joint box
Electronic cable
Support
Calibration source
neck
Lead shielding
water tank
Crystal array
liquid N2
Each crystal 8x8cm,
3Z x 6 segments.
LNGS: Cosmic-ray induced bg.
Tübingen: muon & neutron induced bg.
Heidelberg: Liquid Ar feasibility
München: bg. in electronics & supports

32. Single electron events
Most single-e events deposit energy locally.
A small fraction deposit energy in 2 Ge crystal, since a hard photon is generated at early stage.
Zoom
Blue: electron trajectory
Red: photon trajectory

33. Results on background rejection
Rejection factors on different backgrounds:
With 3Z 6 segments
1 Ge & energy in 10keV window
1 seg. & energy in 10keV window
signal
90%
82%
Co60 in crystal
3.0E-4
2.6E-5
Co60 in cable
1.7E-4
9.6E-6
Ga68 in crystal
9.8E-4
1.2E-4
Pb210 in crystal
<1.0E-4
Tl208 in crystal
2.4E-4
5.0E-5
Tl208 in cable
2.2E-4
8.0E-5
Pulse shape analysis (PSA) is expected to reject more background and possibly save some signal.

34. GERDA is a work in progress: if all goes well, we should be commissioning the cryo system + existing detectors end of next year.
In the 2.5 years I have been at the MPI, I have enjoyed many stimulating and fun discussions with Leo ! He has a deep intuition for physics, and a very clear way of explaining his ideas.