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CUTAPP05 A. Caldwell/MPI


Topics covered: Selected review Why we chose Germanium Where we hope to improve over previous experiments Importance of background reduction Current status of GERDA 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).

Decay rate, nuclear matrix elements: 

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

Decay rate - cont.: 

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

What previous experiments teach us: 

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

Backgrounds - statistical analysis: 

Backgrounds - statistical analysis The discovery potential depends strongly on the background level ! Here is a Bayesian analysis assuming a flat prior for the rate (0-10-24/yr). Discovery is defined by requiring that the probability that R=0 is less than 0.0001. Background rate /kg/yr K-K et al. Just for illustration H-M Background Cuoricino


Heidelberg-Moscow H.V. Klapdor-Kleingrothaus, I.V. Krivosheina, A. Dietz, O. Chkvorets (Heidelberg, Max Planck Inst.) Phys.Lett.B586:198-212,2004 Background: 0.11/keV/kg/yr With pulse shape analysis Known Bi lines 0 DBD signal ??


Heidelberg-Moscow T1/2=1.2 1025 yr A 4.2 signal

Background model in HD-Moscow (diploma thesis Christian Dörr, 2002): 

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 data/MC for Th calibration source Comparison signal data/MC Red=simulation Black = data 100 200 300 [keV] 500 600 700 [keV] 900 1000 1100 [keV] 1300 1400 1500 [keV] result: no indication for background in Ge detector (after 5y), mainly in Cu cryostat, less in Pb

IGEX/Majorana Experiment: 

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




Total Statistics: 10.85 kgxy DBD0 result: T1/2130Te <m> < [0.2÷1.1] eV arXiv:hep-ex/0501034 v1 > 1.8 x 1024 y


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

NEMO3: first results: 

NEMO3: first results First results on 100Mo (650 h) t1/22n (y) = 7.8 ± 0.09 stat ± 0.8 syst  1018 y t1/20n (y) > 6  1022 y 2n spectrum Signal region These data should be very valuable in tuning the nuclear models Very small background, but small mass & poor energy resolution

Proposed experiments: 

Proposed experiments 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 = 867 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% Some of the possible isotopes

Why Germanium: 

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)


Q=2.039 MeV

External backgrounds: 

External backgrounds Artist’s conception Engineer’s conception Suppress 208Tl 2.615 MeV , n,  Reduce external backgrounds to 10-3/keV/kg/yr

Internal Backgrounds: 

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. Dominant decay chain: 68Ge  68Ga via EC (10.6 KeV ) =271 days 68Ga  68Zn via + (90%, 1.9 MeV) +  (0.511 MeV) +  (0.511 MeV) =68 minutes Possibility to distinguish 2.0 MeV  + (s) from 2x1.0 MeV - ?

Internal Backgrounds: 

Internal Backgrounds 60Co after 10 days of activation and 3 years of storage 0.18 mBq/kg  5.4 decays/(kg y) Dominant decay chain: 60Co  60Ni via - (0.316 MeV) +  (1.17 MeV) +  (1.33 MeV) = 5.27 years Possibility to distinguish gammas from electron ? +other stuff: surface contamination, supports and cables, …

Pulse shape, segmentation: 

Pulse shape, segmentation Can we distinguish single versus multiple energy deposits ? Tools: pulse timing, segmentation.

Developments for GERDA: 

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

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

Infrastructures in HALL A: Super-Structure & Water tank

Infrastructures in Hall A: Super-insulated cryogenic vessel : 

Infrastructures in Hall A: Super-insulated cryogenic vessel Cu-cryostat: hanging from neck Cu-cryostat: resting on pads Steel-cryostat: with optimized shielding Two design studies for Cu-cryostat available: 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:2005-002331; 7 companies expressed interest Decision taking Cu vs. steel cryostat: Cu-Steel welding tests and certification

Infrastructure in Hall A: Cryogenic systems for (re-)filling and cooling: 

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

Testing and modification of enriched detectors: 

Testing and modification of enriched detectors November, 2004, in LENS barrack (prior to barrack refurbishment) Co-60 source - absolute efficiency (done) Ba-133 source - dead layer thickness estimation (done) Check of ANG2 (ongoing) Energy resolution at 2.615 MeV

Modification of enriched detectors: 

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

New detectors for Phase II: Procurement of enriched Ge: 

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 30-40 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

MaGe simulations of muon induced backgrounds (GSTR-05-003): 

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

MaGe: MC for Gerda & Majorana: 

MaGe: MC for Gerda & Majorana water tank neck Lead shielding 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 3x7 Ge crystals Electronic joint box Electronic cable Support Calibration source Crystal array

Single electron events: 

Single electron events Blue: electron trajectory Red: photon trajectory Zoom 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.


Pulse shape analysis (PSA) is expected to reject more background and possibly save some signal. Results on background rejection Rejection factors on different backgrounds:


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.

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