1. M. Wójcik Instytut Fizyki, Uniwersytet Jagielloński Instytut Fizyki Doświadczalnej, Uniwersytet Warszawski Warszawa, 10 Marca 2006

2. 74 physicists 13 institutions 5 countries

3. Location of the GERDA Experiment

4. Double Beta decay

5. Double Beta Decay

6. Motivation for GERDA Open questions: What is the absolute mass-scale for neutrinos? Which mass hierarchy is realized in nature? What is the nature of neutrino? Dirac or Majorana Neutrinoless double beta decay experiment has the potential to answer all three questions

7. Absolute mass-scale for neutrinos Especially sensitive ways to measure the neutrino mass 3 H beta-decay, electron energy measurement Mainz/Troisk Experiment: m e < 2.2 eV  KATRIN Cosmology, Large Scale Structure WMAP & SDSS: cosmological bounds  m < 0.8 eV Neutrinoless double beta decay evidence/claims? Majorana mass:  0.4 eV

8. Tritium Experiments

9. Neutrino mas hierarchy value allow to distinguish between NH, IH, QD  (100 – 500) meV – claim of an observation of 0  in 76 Ge suggests quasi-degenerate spectrum of neutrino masses  (20 – 55) meV – calculated using atmospheric neutrino oscillation parameters suggests inverted neutrino mass hierarchy or the normal- hierarchy – very near QD region  (2 – 5) meV – calculated using solar neutrino oscillation parameters would suggest normal neutrino mass hierarchy

10. Neutrino mass hierarchy quasi-degenerate (QD) mass spectrum m min >> (  m 21 2  ) 1/2 as well as m min >>(  m 32 2  ) 1/2

11. Heidelberg-Moscow Experiment Isotope enriched Germanium diodes (86% in 76 Ge)

12. IGEX Experiment Isotope enriched Ge detectors (86 % in 76 Ge)

13. GERDA Phase I use existing 76 Ge (86 %) detectors of HD-M & IGEX  15 kg existing detectors Background, assume 0.01 cts/(keV kg y) Energy resolution (FWHM), assume = 3.6 keV  N bck  0.5 cts for 15 kg y –Klapdor-K.: 28.8  6.9 events in 71.7 kg y  expect 6.0  1.4 cts above N bck For  1 events: signal excluded at 98 % CL

14. Bare Ge crystals for Phase I - As small as possible holder mass - Ultra-pure materials

15. GERDA Phase II 15 kg existing detect. + 20 kg new segmented detect. Verify background index 0.001 cts/(keV kg y) Statistics 3 y x 35 kg  100 kg y Assume energy resolution = 3.6 keV N bck  0.36 counts T 1/2 > 2 x 10 26 y < 0.09 – 0.29 eV

16. Segmented Ge detectors for Phase II - As small as possible holder mass - Ultra-pure materials

17. Hexagonally placed detectors

18. Nuclear Matrix Elements Calculations

19. Our Goal: background index of 0.001 cts/(keV kg y) gigantic step in background reduction needed ~ 100 External background -  from U, Th decay chain, especially 2.615 MeV from 208 Tl in concrete, rock, steel... - neutrons from ( ,n) reaction and fission in concrete, rock and from  induced reactions external background will be reduced by passive and active shield Internal background - cosmogenic isotopes produced in spallation reactions at the surface, 68 Ge and 60 Co with half lifetimes ~year(s) - surface and bulk Ge contamination internal background will be reduced by anticoincidence between segments and puls shape discrimination

20. GERDA

21. Graded shielding of external  backgr. Shielding layerTl concentration ~ 3 m purified water (700 m 3 ) 208 Tl < 1 mBq/kg ~ 4 cm copper kriostat + 3 rd wall 208 Tl < 10 mBq/kg ~ 2 m LN 2 /LAr (50 m 3 ) Tl ~ 0 Shielding and cooling with LN 2 /LAr is best solution ‘reduce all impure material close to detectors as much as possible’  external  / n /  background < 0.001 cts/(keV kg y) for LN will be reached Factor ~ 10 smaller ext. bck. for LAr

22. Background reduction Underground experiment (mion shield) Specific background reduction techniques - mion veto – water Cerenkov detector - photon-electron discrimination - scintillation in kryo-liquid as anticoincidence

23. Internal Backgrounds Cosmogenic 68 Ge product. in 76 Ge at surface: ~1 68 Ge/ (kg d) (Avinione et al., Nucl. Phys B (Proc. Suppl) 28A (1992) 280) 68 Ge  68 Ga  68 Zn T 1/2 271 d 68 min stable Decay EC  + (90%) EC (10%) Radiation X – 10,3 keV  – 2,9 MeV After 6 months exposure at surface and 6 months storage underground  58 decays/(kg y) in 1 st year  Bck. index = 0.012 cts/(keV kg y) = 12 x goal! As short as possible exposure to cosmic radiation

24. Cosmogenic 60 Co production in natural Ge at sea level : 6.5 60 Co/(kg d) Baudis PhD 4.7 60 Co/(kg d) Avinione et al., 60 Co  60 Ni T 1/2 5.27 y Decay  - Radiation  (E max = 2824 keV)  (1172 keV, 1332 keV) After 30 days of exposure at sea level  15 decays/(kg y) Bck. index = 0.0025 cts/(keV kg y) = 2.5 x goal! As short as possible exposure to cosmics Internal backgrounds

25. Internal background reduction Photon – Electron discrimination Signal: local energy deposition – single site event Gamma background: compton scattering – multi site event Anti-coincidence between segments suppr. factor ~10 Puls shape analysis suppr. factor ~2

26. Background of the Ge detector PartSourceRate [10 -3 keV -1 kg -1 y -1 ] Cristal U-238 Th-232 Co-60 Ge-68 Pb-210 (sf) Th-232 (sf) 0.25 0.05 0.03 1.53 0.13 0.17 Holder all (copper) all (teflon) 0.14 0.20 Cable all (copper) all (kapton) 0.02 ~1.5 Sum ~4 Mions and Neutrons at LNGS < 10 -4 cts keV -1 kg -1 y -1

27. Summary GERDA GERDA approved by LNGS – location in Hall A Phase I: use existing detectors, test Klapdor-K. result in 1 year Background level of 0.01 cts/(keV kg y) Expected start of data taking 2008 Phase II: add new segmented detectors  factor 10 in T 1/2 sensitivity Challenging background level of 0.001 cts/(keV kg y) Expected sensitivity ~ 50 meV Background suppression is the key to success!

28. Double beta decay

29. Double beta experiments