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Activity for the Gerda-specific part

This activity focuses on optimizing the setup of the Gerda experiment, specifically the water tank neck lead shielding and muon veto, to reduce background noise. The setup includes a water tank, copper tank, liquid nitrogen, crystals array, and kapton cables.

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Activity for the Gerda-specific part

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  1. Activity for the Gerda-specific part Gerda geometry top m-veto water tank neck lead shielding cryo vessel Description of the Gerda setup including shielding (water tank, Cu tank, liquid Nitrogen), crystals array and kapton cables Ge array

  2. Small flux, small Ge volume: 88 events/kg y Cosmic ray muons (Phase I) Flux at Gran Sasso: 1.1 m/m2 h (270 GeV) MACRO (1995) Further reduced by anti-coincidence with other Ge-crystals and with top (or Cerenkov) m-veto Input energy spectrum Input angular spectrum f from Lipari and Stanev, Phys. Rev. D 44 (1991) 3543 MACRO (1993) Teramo side cosq Energy (keV)

  3. radius 20m – zenit angles up to 68° Generation point of cosmic muons randomly extracted on a circle placed 3m above the GERDA WT top m-veto water tank • plastic scintillator plates of different dimensions and thickness were simulated to find out the optimum configuration of the top muon veto • two positioning of the plate were tried: above the penthouse and between the penthouse and the WT neck lead shielding cryo vessel Ge array The height of the WT is assumed to be 10m (as in the GERDA proposal)

  4. 6m x 3m, rotated 10° 4m x 4m 5m x 5m 6m x 6m centered • the efficiency scale with the area of the plate except for configuration 2 • the top muon veto between the WT and the penthouse must be considered a preferred option with respect to increasing the area of the plate • the top muon veto is less effective than previously estimated • the anticoincidence between the detectors is more effective in suppressing the background threshold 1 meV thickness = 3 cm – has no effect on efficiency

  5. Small flux, small Ge volume: 88 events/kg y Cosmic  flux at LNGS Flux at Gran Sasso: 1.1 m/m2 h (270 GeV) MACRO (1995) Input energy spectrum Input angular spectrum f from Lipari and Stanev, Phys. Rev. D 44 (1991) 3543 MACRO (1993) Teramo side cosq Energy (keV) Gerda Collab. , Jun 27-29, 2005 2) Gerda Background – cosmic muon

  6. Background index (Phase I) – no veto 9 Ge crystals for a total mass of 19 kg; threshold: 50 keV annihilation peak Sum spectrum without and with anticoincidence 5.5 years Energy (MeV) (1.5  2.5 MeV): 3.3·10-3 counts/keV kg y (~4·10-3 counts/keV kg y in H-M simul.) The anticoincidence between 9 crystals reduces the background index of a factor of 3 C. Doerr, NIM A 513 (2003) 596 1.5 MeV 2.5 MeV 1.0·10-3 cts/keV kg y Energy (MeV)

  7. Efficiency of the muon veto Small gain Position makes the difference Stable when changing the physics list No event recorded in crystals deposit less than that Top m-veto efficiency  sensitive to angular distribution

  8. Cerenkov muon veto Threshold 120 MeV  all events cut but two Energy (MeV) Energy deposit in the water (coincidence with detectors) 120 MeV in water (60 cm) correspond to 30,000 ph. Signal above 40-50 p.e. with 0.5% coverage  80-90 PMTs Optimization with MC light tracking has to be done

  9. Simulation of the Heidelberg-Moscow enriched detectors within the MaGe framework Comparison between simulation and experimental data C.Tomei & O. Chkvorets This talk will be also presented by Oleg in the TG1 session

  10. The original HdMo Geometry • Setup 1: 4 enriched Ge detectors (86% enr. in 76Ge) in a common setup: • copper cryostates of electropure copper • detector holder of vespel and teflon • 10 cm LC2 lead shielding • 20 cm low-activity lead • iron box • 10 cm boron-polyethylene • layer of plastic scintillators Geometry taken from previous GEANT3 simulation and converted to C++ This geometry has been used for most recent Heidelberg-Moscow simulations and comparison with their latest experimental data C.Dörr, NIM A 513 (2003)

  11. The HdMo geometry in MaGe • The external shielding has been removed • The detectors have been separated to allow the simulation of a shielding or a collimator Det. 1 0.98 kg Det. 3 2.446 kg ANG1 ANG3 ANG4 ANG2 1 m

  12. The measurements Performed by O. Chkvorets and S. Zhukov on February 2005 inside the old LENS barrack first and in LUNA 1 barrack afterwards. Detectors shielded with 10 cm lead Radioactive sources: 60Co and 133Ba (also 226Ra) H H Z Ge Ge Ge D Measurements with and without lead collimator Protocol and measurements available on the GERDA web site at MPI-K (restricted area)

  13. Comparison for detector 3 – 133Ba Geometry: source 21.3 cm above detector 3

  14. Comparison for detector 3 – 60Co Backscattered peak not reproduced because the simulated geometry does not contain the lead shielding Geometry: source 21.4 cm above detector 3 Difference in counting rate for peaks less than 10%

  15. Comparison for detector 3 – 60Co Normalized knowing the activity of the source Geometry: source 21.4 cm above detector 3

  16. Comparison for detector 3 – 214Bi + 214Pb (from 226Ra source) Geometry: source directly on top of end cap of detector 3

  17. Comparison for detector 3 – 214Bi + 214Pb (from 226Ra source) Geometry: source directly on top of end cap of detector 3

  18. Comparison for detector 3 – 214Bi + 214Pb (from 226Ra source) Geometry: source directly on top of end cap of detector 3

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