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 -vetowater tank

lead shieldingcryo

vessel

neck

Ge array

Cosmic ray muons (Phase I)

Flux at Gran Sasso: 1.1/m2 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 -vetowater tank

lead shieldingcryo

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

Cfg Area [m2] Height [m] Rotation [°]CR radius [m]

Time [y]

1 4x4 8 0 8 3.1

2 6x3 8 10 8 2.59

2a 6x3 8 190 8 2.59

3 5x5 8 0 8 2.59

3a 5x5 5.2 0 8 2.59

3b 5x5 8 0 20 5.53

3c 5x5 5.2 0 20 5.37

4 6x6 8 0 8 2.59

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, 2005 2) Gerda Background – cosmic muon

Cosmic flux at LNGS

Flux at Gran Sasso: 1.1/m2 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 veto9 Ge crystals for a total mass of 19 kg; threshold: 50 keV

Energy (MeV)

5.5 yearsSum

spectrum without and

with anticoinciden

ce

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) 5961.5 MeV 2.5 MeVThe

anticoincidence between 9 crystals

reduces the background index

of a factor of 31.0·10-3 cts/keV kg y

Efficiency of the muon vetoBackground index

(cts/keV kg y)

No cuts 3.3 · 10-3

Ge anti-coincidence 1.0 · 10-3

Ge anti-coincidenceTop -veto (above penthouse)

9.0 · 10-4

Ge anti-coincidenceTop -veto (below penthouse)

4.4 · 10-4

Cerenkov -veto (thr = 120 MeV, 30,000 photons)

< 3 · 10-5 (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 40-50 p.e. with 0.5% coverage 80-90 PMTs

Optimization with MC light tracking has to be done

Simulation of the Heidelberg-Moscow enriched detectors within the MaGe

framework

C.Tomei & O. ChkvoretsThis talk will be also presented by Oleg in the TG1 session

Comparison between

simulation and experimental

data

Setup 1Setup 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

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. 1

0.98 kg

Det. 3

2.446 kg

• The external shielding has been removed

• The detectors have been separated to allow the simulation of a shielding or a collimator

1 m

ANG1 ANG3

ANG4ANG2

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

Ge

H

Ge Ge

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 – 133Ba

Geometry: source 21.3 cm above detector 3

Comparison for detector 3 – 60Co

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 – 60Co

Geometry: source 21.4 cm above detector 3

Normalized knowing the activity of the source

Comparison for detector 3 – 214Bi + 214Pb (from 226Ra source)

Geometry: source directly on top of end cap of detector 3

Comparison for detector 3 – 214Bi + 214Pb (from 226Ra source)

Geometry: source directly on top of end cap of detector 3

Comparison for detector 3 – 214Bi + 214Pb (from 226Ra source)

Geometry: source directly on top of end cap of detector 3