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CUTAPP05 A. Caldwell/MPI

CUTAPP05 A. Caldwell/MPI. 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

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CUTAPP05 A. Caldwell/MPI

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  1. CUTAPP05 A. Caldwell/MPI

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

  4. Decay rate - cont.  = (G(Q,Z) |Mnucl|2 mee2)-1fix mee=50 meV X 1026 years 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 (0-10-24/yr). Discovery is defined by requiring that the probability that R=0 is less than 0.0001. Just for illustration Background rate /kg/yr H-M Background K-K et al. Cuoricino

  7. 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 0 DBD signal ?? Known Bi lines With pulse shape analysis

  8. Heidelberg-Moscow A 4.2 signal T1/2=1.2 1025 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 100 200 300 [keV] 500 600 700 [keV] 900 1000 1100 [keV] result: no indication for background in Ge detector (after 5y), mainly in Cu cryostat, less in Pb 1300 1400 1500 [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. 11 modules 4 detector each, 5x5x5 cm3 790 g TeO2 crystals Total mass ~41 kg + 2 modules 9 detector each, 3x3x6 cm3 330 g TeO2 crystals Cuoricino

  12. Background (@DBD0): 0.18 ± 0.01 c/keV/kg/y Total Statistics: 10.85 kgxy arXiv:hep-ex/0501034 v1 DBD0 result: T1/2130Te <m> < [0.2÷1.1] eV > 1.8 x 1024 y

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

  14. NEMO3: first results First results on 100Mo (650 h) 2n spectrum Signal region t1/22n(y) = 7.8 ± 0.09 stat± 0.8 syst 1018 y t1/20n(y) > 6  1022 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 keVnat. 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 keVnat. 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

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

  19. From B. Swchingenheuer MPI-K MeV 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 - ?

  20. MeV 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, …

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

  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:2005-002331; 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 2.615 MeV • 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

  28. 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

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

  30. 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

  31. 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

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

  33. 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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