LArGe setups

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LArGe setups
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Simulation of LArGe setup at MPIK
Simulation of LArGe integrated in the MaGe
framework
Goal complete simulation of the scintillation
photons
Simplified toy-geometry
understand better shadowing effects and optimize
the detector packing
LAr scintillation large yield (40,000 ph/MeV)
but in the UV (128 nm)
Possibly, understand and derive optical
properties of interest (e.g. reflectivity of Ge
crystals), that are poorly known in the UV
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Optical physics
Geant4 (and then MaGe) is able to produce track
optical photons (e.g. from scintillation or
Cerenkov)

• Processes into the game
• scintillation in LAr
• Cerenkov in LAr
• boundary and surface effects
• absorption in bulk materials
• Rayleigh scattering
• wavelenght shifting

Refraction index of LAr
Properties of all interfaces (reflectivity,
absorbance)
Absorption length of LAr
Rayleigh length of LAr
Emission spectrum of VM2000 (measured _at_MPIK) and
QE
The optical properties of materials and of
surfaces (e.g. refraction index, absorption
length) must be implemented ? often unknown (or
poorly known) in UV
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Properties of LAr
Data kindly provided by ICARUS people
Absorption length in LAr not known ? ICARUS does
not see effect in one semi-module, so L ? 1 or a
few meters
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Output from the simulation
Frequency spectrum of photons at the PM (to be
convoluted with QE!)
The ratio between the LAr peak and the optical
part depends on the WLS QE critical parameter
Scintillation yield ? 40,000 ph/MeV
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Measurement with collimated 57Co
LArGe setup irradiated with external collimated
57Co source
Measurement
From measurement 122 keV correspond to 24.5 p.e.
Drawback the simulation is very slow (a few
seconds per 122-keV event)
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LArGe set-up at Gran Sasso
The geometry for the LArGe set-up at Gran Sasso
has been implemented in MaGe
It includes the shielding layers, the cryo-liquid
and the Ge crystals
Number of crystals columns and plans tunable by
macro (? interfaced with the general Gerda
geometry tools)
Available in MaGe and ready for physics studies
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Optimization for Phase I
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Gerda geometry in MaGe
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
Tunable by macro
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Crystal packing
column gap
A 3x3 crystal array will be used for Phase I.
The supporting structures are under definition
and must be optimized
(? Munich group for Phase II)
2 parameters to play with
Monte Carlo to study close vs. loose packing.
Close packing anti-coincidence more effective,
but higher total rate (crystals see the
supporting structures of neighbours)
column distance
depends on contamination and on its position
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Crystal packing 60Co contamination
Position 1 60Co 1 cm above the center of one of
the crystals of the middle plane
Strategy run MaGe with different column gap and
column distance, see the probability to find
energy deposition in 2.0 ? 2.1 MeV
Anticoincidence
Total
probability per decay
probability per decay
With anti-coincidence dvertical ? 4 cm
(plateau), dhorizontal ? as small as possible
Total rate crystals as fas as possible
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Crystal packing 60Co contamination
Position 2 60Co 1 cm above the corner of one of
the crystals of the middle plane
Anticoincidence
probability per decay
Total
probability per decay
With anti-coincidence dvertical ? 4 cm
(plateau), dhorizontal ? 2 cm (plateau)
Probability is weakly sensitive to the horizontal
distance (more sensitive to vertical distance)
Total rate crystals as fas as possible
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Crystal packing 208Tl contamination
Position 1 208Tl 1 cm above the center of one
of the crystals of the middle plane
With anti-coincidence close packing preferable
Total rate always decreases with crystal
distance. With anti-coincidence, the optimal
distance depends on source location
Next step introduce the Phase I supporting
structures geometry in MaGe
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Radon contamination in the water
Simulated 800M 214Bi decays uniformly in the
water tank
2 cts in 1 MeV
Energy (MeV)
Energy (MeV)
Background index lt 10-2 R cts/kg keV y (95
CL)
222Rn rate in Bq/m3
For 25 mBq/m3 ? lt 2-3 10-4 cts/kg keV y (95
CL)
For 5 mBq/m3 ? lt 5 10-5 cts/kg keV y (95 CL)
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The status of MaGe

• MaGe is currently manteined and debugged jointly
  with the Majorana people. The code in the CVS is
  regularly tagged
• An official release, i.e. a stable MaGe version
  intended for users rather than for developers
  is going to be completed
• The physics capability has been extended to
  include the generation and tracking of optical
  photons
• An interface to the MUSUN generator for cosmic
  ray muons has been included (to be committed in
  CVS)
• New geometries and new i/o schemes have been
  added to handle the new Gerda test stands (at
  Munich, MPIK and GS)
• Validation studies with test-stand data are
  ongoing
• Together with Majorana people, we placed the
  request for MaGe dedicated talk (or a poster) to
  the Organizers of the next TAUP Conference
• Already used for physics studies and ready for
  others

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Measurement with collimated 57Co
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Measurement with collimated 57Co