LArGe setups

Simulation of LArGe setup at MPIKSimulation of LArGe integrated in the MaGe

frameworkSimplified toy-

geometryGoal: complete

simulation of the scintillation photons

understand better shadowing effects and optimize the detector

packing

Possibly, understand and derive optical properties of interest (e.g. reflectivity of Ge

crystals), that are poorly known in the UV

LAr scintillation: large yield (40,000 ph/MeV) but in the UV

(128 nm)

PMT

crystal

reflector and WLS

tank

Optical physicsGeant4 (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

The optical properties of materials and of surfaces (e.g. refraction index, absorption length) must be implemented

often unknown (or poorly known) in UV

Refraction index of LAr

Properties of all interfaces (reflectivity,

absorbance)

Absorption length of LAr

Rayleigh length of LAr

Emission spectrum of VM2000 (measured @MPIK)

and QE

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

Rayleigh scattering

length

20 cm at 128 nm

Wavelength (nm)

Rayle

igh length

(m

)

LAr refraction

index

1.5 at 128 nm

1.25 at visible

Wavelength (nm)

Refr

act

ion index

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

Ar peak

VM2000 emission

Cerenkov spectrum

34 p.e. (60%

WLS QE)

Measurement with collimated 57CoLArGe setup irradiated with external collimated 57Co source

Measurement:

Drawback: the simulation is very slow (a few seconds

per 122-keV event)

From measurement: 122 keV correspond to 24.5 p.e.

Simulation of 122 keV line: (PMT QE included)

46 p.e. (80%

WLS QE)

LArGe set-up at Gran Sasso

Number of crystals columns and plans tunable by macro

( interfaced with the general Gerda geometry tools)

Available in MaGe and ready for physics

studies

The geometry for the LArGe set-up at Gran Sasso has been implemented in

MaGeIt includes the shielding

layers, the cryo-liquid and the Ge crystals

Optimization for Phase I

Gerda geometry in MaGe

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 Tunable by macro

Crystal packingA 3x3 crystal array will be

used for Phase I.

The supporting structures are under definition and

must be optimized

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)

2 parameters to play with:

column gap

column distance

( Munich group for Phase II)

depends on contamination and on its position

Crystal packing: 60Co contaminationPosition #1: 60Co 1 cm above the center of one of the crystals of the

middle planeStrategy: run MaGe with different column gap and column distance, see the

probability to find energy deposition in 2.0 2.1 MeV

Total

Anticoincidence

With anti-coincidence: dvertical 4 cm (plateau), dhorizontal as small as

possibleTotal rate: crystals as fas as possible

pro

bab

ility

per

deca

y

pro

bab

ility

per

deca

y

Crystal packing: 60Co contaminationPosition #2: 60Co 1 cm above the corner of one of the crystals of the

middle plane

Total

With anti-coincidence: dvertical 4 cm (plateau), dhorizontal 2 cm (plateau)

Total rate: crystals as fas as possible

pro

bab

ility

per

deca

y

Anticoincidence

pro

bab

ility

per

deca

y

Probability is weakly sensitive to the horizontal distance (more sensitive to

vertical distance)

Crystal packing: 208Tl contaminationPosition #1: 208Tl 1 cm above the center of one of

the crystals of the middle plane

Total

Anticoincidence

With anti-coincidence: close packing preferable

pro

bab

ility

per

deca

y

pro

bab

ility

per

deca

y

Total rate always decreases with crystal distance. With anti-coincidence, the optimal distance depends on source &

locationNext step: introduce the Phase I supporting structures geometry in MaGe

Radon contamination in the water

Energy (MeV)

Simulated 800M 214Bi decays uniformly in the water tank

Energy (MeV)

2 cts in 1 MeV

Background index < 10-2 R [cts/kg keV y] (95% CL)222Rn rate in Bq/m3

For 25 mBq/m3 < 2-3 · 10-4 cts/kg keV y (95% CL)For 5 mBq/m3 < 5 · 10-5 cts/kg keV y (95% CL)

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

Measurement with collimated 57Co

Measurement with collimated 57Co