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

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

top  -veto water tank lead shielding cryo vessel neck Ge array Generation point of cosmic muons randomly extracted on a circle placed 3m above the GERDA WT radius 20m – zenit angles up to 68° 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 The height of the WT is assumed to be 10m (as in the GERDA proposal)

6m x 3m, rotated 10° 4m x 4m 5m x 5m 6m x 6m centered CfgArea [m 2 ]Height [m]Rotation [°]CR radius [m]Time [y] 14x x a6x x a5x b5x c5x x thickness = 3 cm – has no effect on efficiency 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

Gerda Collab., Jun 27-29, 20052) Gerda Background – cosmic muon Cosmic  flux at LNGS Flux at Gran Sasso: 1.1  /m 2 h (270 GeV) Small flux, small Ge volume: 88 events/kg y Input energy spectrum from Lipari and Stanev, Phys. Rev. D 44 (1991) 3543 Energy (keV) Input angular spectrum cos   Teramo side MACRO (1995) MACRO (1993)

Background index (Phase I) – no veto 9 Ge crystals for a total mass of 19 kg; threshold: 50 keV Energy (MeV) 5.5 years Sum spectrum without and with anticoincidence Energy (MeV) (1.5  2.5 MeV): 3.3·10 -3 counts/keV kg y annihilation peak (~4·10 -3 counts/keV kg y in H-M simul.) C. Doerr, NIM A 513 (2003) MeV2.5 MeV The anticoincidence between 9 crystals reduces the background index of a factor of 3 1.0·10 -3 cts/keV kg y

Efficiency of the muon veto Background index (cts/keV kg y) No cuts3.3 · Ge anti-coincidence1.0 · Ge anti-coincidence Top  -veto (above penthouse) 9.0 · Ge anti-coincidence Top  -veto (below penthouse) 4.4 · Cerenkov  -veto (thr = 120 MeV, 30,000 photons) < 3 · (95% CL) Top  -veto efficiency  sensitive to angular distribution Position makes the difference Small gain No event recorded in crystals deposit less than that Stable when changing the physics list

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

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

Setup 1 Setup 1: 4 enriched Ge detectors (86% enr. in 76 Ge) 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 The original HdMo Geometry This geometry has been used for most recent Heidelberg-Moscow simulations and comparison with their latest experimental data C.Dörr, NIM A 513 (2003) Geometry taken from previous GEANT3 simulation and converted to C++

The HdMo geometry in MaGe Det kg Det kg The external shielding has been removed The detectors have been separated to allow the simulation of a shielding or a collimator 1 m ANG1ANG3 ANG4 ANG2

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: 60 Co and 133 Ba (also 226 Ra) H Ge H Measurements with and without lead collimator D Z Protocol and measurements available on the GERDA web site at MPI-K (restricted area)

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

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

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

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

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

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