Transcript Document

Activity for the Gerda-specific part
Gerda geometry
top m-veto
water tank
neck
cryo
vessel
lead
shielding
Ge array
Description of the Gerda
setup including shielding
(water tank, Cu tank, liquid
Nitrogen), crystals array and
kapton cables
Cosmic ray muons (Phase I)
Flux at Gran Sasso: 1.1 m/m2 h (270 GeV)
MACRO (1995)
Small flux, small Ge volume: 88 events/kg y
Further reduced by anti-coincidence with other Gecrystals and with top (or Cerenkov) m-veto
Input energy spectrum
from Lipari and
Stanev, Phys. Rev.
D 44 (1991) 3543
f
Input angular spectrum
MACRO (1993)
Teramo
side
Energy (keV)
cosq
radius 20m – zenit angles up to 68°
top m-veto
water tank
neck
cryo
vessel
lead
shielding
Generation point of
cosmic muons randomly
extracted on a circle
placed 3m above the
GERDA WT
• 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
Ge array
The height of the WT is assumed to be 10m (as in the GERDA proposal)
4m x 4m
5m x 5m
6m x 6m
centered
6m x 3m,
rotated 10°
threshold
1 meV
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
Cosmic m flux at LNGS
Flux at Gran Sasso: 1.1 m/m2 h (270 GeV)
Small flux, small Ge volume:
Input energy spectrum
from Lipari and
Stanev, Phys. Rev.
D 44 (1991) 3543
f
MACRO (1995)
88 events/kg y
Input angular spectrum
MACRO (1993)
Teramo
side
Energy (keV)
Gerda Collab. , Jun 27-29, 2005
cosq
2) Gerda Background – cosmic muon
Background index (Phase I) – no veto
9 Ge crystals for a total mass of 19 kg; threshold: 50 keV
annihilation
peak
(1.5  2.5 MeV):
3.3·10-3
Sum spectrum
without and
with
anticoincidence
5.5 years
Energy (MeV)
counts/keV kg y
(~4·10-3 counts/keV kg y in H-M simul.)
1.5 MeV
C. Doerr, NIM A 513 (2003) 596
2.5 MeV
Energy (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 cuts
3.3 · 10-3
Ge anti-coincidence
1.0 · 10-3
Ge anti-coincidence
Top m-veto (above penthouse)
9.0 · 10-4
Ge anti-coincidence
Top m-veto (below penthouse)
4.4 · 10-4
Cerenkov m-veto
(thr = 120 MeV, 30,000 photons)
< 3 · 10-5 (95% CL)
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
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
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
The original HdMo Geometry
Setup 1: 4 enriched Ge detectors (86% enr. in
• 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
76Ge)
in a common setup:
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)
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
Det. 3
0.98 kg
2.446 kg
ANG1
ANG3
ANG2
1m
ANG4
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
H
Ge
and
133Ba
(also
226Ra)
H
Ge
Z
Ge
D
Measurements with and without lead collimator
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 –
Backscattered
peak not
reproduced
because the
simulated
geometry does
not contain the
lead shielding
60Co
Geometry: source 21.4 cm
above detector 3
Difference in counting rate for peaks less than 10%
Comparison for detector 3 –
60Co
Normalized knowing the
activity of the source
Geometry: source 21.4 cm above 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
Comparison for detector 3 – 214Bi +
214Pb (from 226Ra source)
Geometry: source directly on top of end cap of detector 3