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GERDA, the GERmanium Detector Array for the search of neutrinoless bb decay in 76 Ge

GERDA, the GERmanium Detector Array for the search of neutrinoless bb decay in 76 Ge. L. Pandola INFN, Gran Sasso National Laboratories for the GERDA Collaboration. PANIC Conference, Santa Fe, NM, October 24 th 2005. D L = 2 process. 0 : (A,Z)  (A,Z+2) + 2e -. p.

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GERDA, the GERmanium Detector Array for the search of neutrinoless bb decay in 76 Ge

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  1. GERDA, the GERmanium Detector Array for the search of neutrinoless bb decay in 76Ge L. Pandola INFN, Gran Sasso National Laboratories for the GERDA Collaboration PANIC Conference, Santa Fe, NM, October 24th 2005

  2. DL = 2 process 0: (A,Z)  (A,Z+2) + 2e- p masses of A=76 nuclei n W- e- Uei, i=1,2,3 neR nM neL Uei e- W- n p only possible if neutrino is a massive Majorana particle coupling ~ 76Ge  76Se + 2e- + 2neDL=0 ~ 1021 years measured ! Motivations for 0n2b Luciano Pandola

  3. The experiment will be hosted in the Gran Sasso National Laboratory, under the Gran Sasso mountain (Italy), 3800 m w.e. cosmic m flux reduced of a factor 106 GERDA experiment at Gran Sasso The GERmanium Detector Array experiment will look for 0n2b decay in 76Ge using HP-Ge detectors enriched in 76Ge GERDA Collaboration 60 physicists 12 institutions Italy, Germany, Russia Luciano Pandola

  4. sum of electron kinetic energies Sensitivity: single site events 2039 keV • = detection efficiency a = bb isotope fraction  enrichment m = mass of detector in kg t = measurement time in years • B = background index in cts/(keV kg y) • R = energy resolution at Qbb in keV Qbb Advantages of Ge: m t • High resolution (<4 keV @ Q) • no background from 2-mode • Signal discrimination methods • single site vs. multiple site events segmentation & pulse shape e a (y) > 4.3x1024 B R @ 90% C.L. Ultra-low background techniques available Phased approach increment of target mass What do we look for? Ge-76: source = detector (diode) Luciano Pandola

  5. Klapdor-K. et al, Phys.Lett. B586(2004)198 Qbb > 1.57 · 1025y (90% C.L.) The current situation Heidelberg-Moscow at Gran Sasso 5 Ge detectors (m= 10.9 kg, a = 86%) S = 71 kg · y , B = 0.2 c/keV kg y Positive evidence: = (0.69 – 4.2) · 1025 y (3s) (2004) < mee> = 0.1 – 0.9 eV GERDA goal: confirm or reject this claim with high statistical confidence within 1 year IGEX at Canfranc 3 Ge detectors (m= 6 kg, a = 86%) S = 8.8 kg · y , B = 0.2 c/keV kg y Gonzales et al. Nucl. Phys. B (P.S.) 87 (2000) 278 Projects with other isotopes (e.g. 130Te) are also ongoing Luciano Pandola

  6. Phases and physics reach of Gerda Our Goal: background index 10-3 cts/(keV kg y) 10-3 / (keV·kg·y) 2·1026 (90 % CL) 10-1 / (keV·kg·y) Phase I: existing detectors of HM & IGEX, establish background reduction Phase II: new detectors Phase III: worldwide new collaboration O(ton) experiment 1027 yCooperation with Majorana 3·1025 (90 % CL) H-M bck Phase-II HdM & IGEX +new diodes Phase-I HdM & IGEX KK claim 2007/8 2010 Luciano Pandola

  7. ... how to reach 10-3 cts/keV kg y? The background index of10-3 counts/keV·kg·y is 2 orders of magnitude smallerthan the current state-of-the-art ! ~ 0.06/cm²s (2.6 MeV ) Learn from Borexino! Heusser, Ann, Rev. Nucl. Part. Sci. 45 (1995) 543 ~5.6 m Shield against externalgoperating naked Ge crystals suspended in high purity liquid N2/Ar < 0.3 Bq 222Rn/m3 10-3 (kg keV y) -1 (same concept of GENIUS and GEM) LN2, =0.8 g/cm3 Too large for GS  gradedshielding (water buffer) Luciano Pandola

  8. Gerda baseline design Clean room lock Water tank / buffer/ muon veto Advantages of water: - better shielding than LNitrogen - cheaper - safer - neutron moderator - Cerenkov medium for 4p muon veto Vacuum insulated copper vessel Liquid N/Ar External background < 10-3 cnt/(keV kg y) for LN2, factor ~10 smaller for LAr Ge Array Luciano Pandola

  9. water tank top m-veto neck lead shielding cryo vessel Ge array Backgrounds in Gerda 180 days exposure after enrichment + 180 days underground storage derived from measurements and MC simulations 30 days exposure after crystal growing For Phase II: B  10-3 cts/(keV kg y)  additional reduction Luciano Pandola

  10. Background reduction techniques • Muon Veto • Anti-coincidence between detectors • Segmentation of readout electrodes (Phase II) (6  3z) • Pulse shape analysis (Phase I+II) • Coincidence in decay chain (68Ge) • Scintillation light detection (LAr option) • Wait for decay of isotopes (68Ge) Luciano Pandola

  11. ~14 m 14.80 m Location of Gerda Hall A of the Gran Sasso Laboratory, in front of LVD Luciano Pandola

  12. Outlook and conclusions The GERDA experiment will search for 76Ge 0n2b decay at Gran Sasso (Italy) with background level of 10-3 counts/keV kg y Experiment approved by LNGS; substantial funding from MPI, Russia (in-kind), INFN, BMBF Start of construction in 2006; detector commissioning/start data taking 2007 Test the result from Klapdor-Kleingrothaus in 1 year (phase I). Then phase II  2 · 1026 y Co-operation with Majorana (MC, LArGe) very positive: mutual benefit!  Phase III Luciano Pandola

  13. Phases and physics reach of Gerda Phase I: Phase II: Phase III: F.Feruglio, A. Strumia, F. Vissani, NPB 659 | mee| in eV Lightest neutrino (m1) in eV To test inverted & degenerate hierarchy need sensitivity <50 meV Luciano Pandola

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