LArGe setups

1. LArGe setups

2. tank PMT reflector and WLS crystal 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

3. 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 @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

4. LAr refraction index Refraction index Rayleigh length (m) Rayleigh scattering length 1.5 at 128 nm 1.25 at visible 20 cm at 128 nm Wavelength (nm) Wavelength (nm) 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

5. Ar peak VM2000 emission Cerenkov spectrum 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

6. Simulation of 122 keV line: (PMT QE included) 46 p.e. (80% WLS QE) 34 p.e. (60% WLS QE) 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)

7. 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 planstunable by macro ( interfaced with the general Gerda geometry tools) Available in MaGe and ready for physics studies

8. Optimization for Phase I

9. 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

10. 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

11. 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

12. 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

13. Anticoincidence Total probability per decay probability per decay 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

14. 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 < 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)

15. 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

16. Measurement with collimated 57Co

17. Measurement with collimated 57Co