tomei

GERDA: The GERmanium Detector Array for the search of neutrinoless  decay of 76Ge at LNGS: 

GERDA: The GERmanium Detector Array for the search of neutrinoless  decay of 76Ge at LNGS DBD06 - Valencia, April 28 & 29 Claudia Tomei (LNGS) on behalf of the GERDA collaboration

Slide2: 

What is GERDA? Cosmic m flux ~ 1.1 /m² h Gamma flux (2.6 MeV) ~ 0.03 /cm²s Neutron flux from rock ~ 4 · 10-6 /cm²s The GERDA experiment will look for 0n2b decay in 76Ge using HP-Ge detectors enriched in 76Ge at the Gran Sasso National Underground Laboratory. GERDA Collaboration 80 physicists 13 institutions Italy, Germany, Russia

The neutrinoless bb decay: 

The neutrinoless bb decay Neutrino as Majorana particle Effective neutrino mass Neutrino mass hierarchy: inverted or normal mee = |i Uei ² mi | Uei complex:  sensitive to CP phases  cancellation possible 76Ge  76Se + 2 e-

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The current situation for 76Ge Positive evidence from the data of the Heidelberg-Moscow experiment at Gran Sasso [K.-Kleingrothaus et al, Phys.Lett. B586(2004)198] 5 Ge detectors (m = 10.9 kg, a = 86%) S = 72 kg · y , B = 0.2 c/keV kg y Limit from the data of the IGEX experiment at Canfranc [Gonzales et al. Nucl. Phys. B (P.S.) 87 (2000) 278] 3 Ge detectors (m = 6 kg, a = 86%) S = 8.8 kg · y , B = 0.2 c/keV kg y Projects with other isotopes [CUORICINO (130Te) ongoing] are necessary to confirm the claim independently. GERDA 1st goal: confirm or reject the claim with high statistical confidence within 1 year

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Detector and Signal Advantages of Ge: High resolution (<4 keV @ Q) no background from 2-mode Single/multiple site discrimination methods segmentation & pulse shape Ultra-low background techniques available 76Ge: source = detector 86%

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10-3 / (keV·kg·y) 10-1 / (keV·kg·y) Phase-I HdM & IGEX 3·1025 (90 % CL) Phase-II HdM & IGEX + new diodes 2·1026 (90 % CL) KK claim 2007/8 2010 Phases and physics reach of Gerda Goal on background index 10-3 cts/(keV kg y) H-M bck Phase I: existing enriched detectors from HM & IGEX, establish background reduction Phase II: new detectors Phase III: worldwide new collaboration O(ton) experiment  1027 y in Phase I limited by contaminations in Ge 10-2 cts/(keV kg y)

Slide7: 

F.Feruglio, A. Strumia, F. Vissani, NPB 659 Phases and physics reach of Gerda To test inverted & degenerate hierarchy need sensitivity < 10 meV |mee| in eV Lightest neutrino (m1) in eV Phase I: Phase II: Phase III:

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LN2, =0.8 g/cm3 ~5.6 m The strategy of GERDA is to operate naked Ge crystals suspended in high purity liquid N2/Ar (same concept of GENIUS and GEM) Too large for GS  graded shielding (water buffer) The background index of 10-3 counts/keV·kg·y is 2 orders of magnitude smaller than the current state-of-the-art ! Heusser, Ann, Rev. Nucl. Part. Sci. 45 (1995) 543 How to reduce the background? High Purity Liquid Nitrogen < 0.3 Bq 222Rn/m3 (from Borexino)

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Clean room lock Vacuum insulated copper vessel Water tank / buffer/ muon veto Liquid N/Ar Ge Array Gerda baseline design - better shielding than Liquid Nitrogen - cheaper safer - neutron moderator - Cerenkov medium for muon veto External background < 10-3 cnt/(keV kg y) for LN2, factor ~10 smaller for LAr Advantages of water: 10 m 8.9 m

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

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Background estimation: external sources Phase II : 21 true coaxial detectors (total mass 44 kg) arranged in 7 strings of 3 crystals each. Optional 18-fold (6f,3z) segmentation for the crystals. Phase I : 9 detectors (total mass 19 kg) arranged in 2 strings. Anticoincidence between crystals. MC GEANT4 simulations

Slide12: 

Background estimation: internal sources Phase II : 21 true coaxial detectors (total mass 44 kg) arranged in 7 strings of 3 crystals each. Optional 18-fold (6f,3z) segmentation for the crystals. Monte Carlo background model and 0 signal for Phase II: Exposure 45 kg years Background index 10-3 cts/keV/kg/y in ROI T1/2(0) = 1.6 1025 y

Status of GERDA: Locations: 

Status of GERDA: Locations Underground detector laboratory (LArGe-facility)

Status of GERDA: Infrastructures for Phase I : 

Status of GERDA: Infrastructures for Phase I WT tender opened in December 05, Contract completion: end of May Construction starting by end of 2006 Water Tank Muon Veto 5 x 5 m2 ~80 PMTs

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Super-insulated copper cryostat Vacuum insulated stainless steel cryostat with internal copper or lead shield Status of GERDA: Cryostat

Underground detector laboratory (LArGe facility) for maintenance and measurements. : 

Transportation of the IGEX detectors by van from Canfranc to LNGS (18 hours of exposure to cosmic rays) on Nov. 17, 2005. Status of GERDA: Phase I Detectors Underground detector laboratory (LArGe facility) for maintenance and measurements. Operations/Measurements carried out: Detector maintenance (heat and pump cycles, etc. ) Leakage current Energy resolution Efficiencies 8 enriched Ge detectors from the IGEX and Heidelberg-Moscow experiments (total mass 17.9 kg) underground at LNGS All detectors are performing well! Transformation of enriched detectors started in April

Procurement of enriched Ge: 

Procurement of enriched Ge Enrichment of 37.5 kg Ge-76 completed in Sep.05 Specially designed protective steel container reduces activation by cosmic rays by factor 20 Transportation of Material to Europe by truck for further processing completed Test transportation March 05 Status of GERDA: Phase II Detectors

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Status of GERDA: Phase II Detectors Development of true-coaxial natural segmented detectors ongoing. Choice of the segmentation (12/18-fold) still to be made. Available propotypes: - 6–fold– segmented - 18–fold (6-; 3-z) segmented Development of the suspension system also ongoing and well advanced. Prototypes available for testing. Kapton or other substrate

Slide19: 

collaboration of Gerda and Majorana MC groups for the development of a common framework based on Geant4 Background simulations with MaGe (common Majorana–Gerda Geant4 MC framework) Description of the Gerda setup including shielding (water tank, Cu tank, liquid Nitrogen), crystals array and kapton cables

Slide20: 

Conclusions GERDA is designed to search for the neutrinoless bb decay of 76Ge at the Gran Sasso Underground Laboratory. It will operate naked enriched germanium detectors in a cryogenic liquid, running quasi background free (10-3 cts/kg keV y), and aiming at a 100 kg y exposure. Phased approach: test the result from the H-M experiment in 1 year, then move to Phase II  2 · 1026 y Contruction will start in 2006. First data taking is expected in 2008.