Muons crossing the detector (2)

1. crystals surrounded by low-Z material (low n yield from m) water and nitrogen are effective neutron moderators Spectrum of neutrons in the crystals from QGSP_BIC_ISO physics list (good for m-induced neutrons). Agreement with FLUKA within a factor of 2 Qbb Integral: 1.4 n/kg y Events/bin/5.4 y (n,n’) thr Above Qbb: 0.6 n/kg y [Araujo et al. NIM A 545 (2005) 398] Thermal:0.02 n/kg y Log(Energy/keV) Muons crossing the detector (2) The contribution coming from neutrons and hadronic showers is < 0.1 %. Due to the specific Gerda set-up: In the assumptions that all neutrons above threshold give (n,n’) interaction, neutron signal is conservatively< 10% of the EM signal (without any cut)

2. Gerda water tank radius distance from track (m) Muons interacting in the rock Estimate the contribution from high-energy neutrons produced in the surrounding rock by cosmic ray m’s Spectrum and total flux (~ 300 n/m2y) from Wulandari et al., hep-ph/0401032 (2004)  agrees with LDV measurements Background: ~ 4 · 10-5 cts/keV kg y (without any cut: can be further reduced by anti-coincidence) LVD, hep-ex/9905047 Water and nitrogen are effective neutron moderators Conservative estimate: the distance m-n is <R> = 0.6 m (from LVD)  good chances that neutrons in the crystal are accompainedby the primary m in the water (veto is effective!)

3. Mu-induced activation Muon-induced interactions can create long-lived (> ms) unstable isotopes in the set-up materials with Q > Qbb cannot be vetoed or shielded against Isotopes in the crystals are relevant (detected with high-efficiency). From the MC  6· 10-5cts/keV kg y m- and p- capture n capture, g inelastic Isotopes in LN2 (12B, 13N, 16N), copper (60Co, 62Cu) and water (16N, 14O, 12B, 6He, 13B) give contributions below 10-6 cts/keV kg y Notice: 16N production rate in water is in good agreement with FLUKA (& data from SK) [hep-ph/0504227]  good MC cross-check

4. Neutrons from rock radioactivity: flux: ~ 3.8 10-6 n/cm2 s In water, flux reduced exponentially with <R> ~ 5 cm (2 m of LAr: only a factor of 2!) Then, 2 m of nitrogen suppress of a factor of 150 If a neutron enters in the water, it does not get out! Concern: neutrons channeling through the neck No extensive simulation, only rough estimate LN2 suppression vertical neutrons (?) surface flux FGe~(40 cm)2 p 3.8 10-6 n/cm2s  0.0065  0.02 Neutrons from fission and (a,n)  ~ 0.2 neutrons/day 3 times higher than m-induced flux thermal component ( 77Ge) Specific MC needed

5. Materials & masses in Phase II set-up

6. Measured activities in materials [1] estimate!

7. Background estimation [1] 20 keV window

8. Plan for further studies in Munich Pulse shape simulation and analysis first results show suppression ~4 at 90% signal efficiency for photons Ensemble tests based on MaGe and statistical analysis Implementation of test-stands geometries into MaGe (for local MPI set-ups) Neutron studies (m-produced and from radioactivity)

9. 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

10. 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

11. Idea: collaboration of the two MC groups for the development of a common framework based on Geant4 avoid the work duplication for the common parts (generators, physics, materials, management)  mjgeometry mjio Generator, physics processes, material, management, etc.  provide the complete simulation chain gerdageometry gerdaio  more extensive validation with experimental data runnable by script;flexible for experiment-specific implementation of geometry and output;  The MaGe framework

12. 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)

13. minimum GS coverage neck Pb plate shadow Optimization of Cerenkov veto Assumptions on Cerekov veto threshold: 120 MeV(~60 cm) Input angular spectrum 40 p.e. (0.5% cov + VM2000)  80 PMTs Detailed Monte Carlo studies (Tuebingen and Dubna) with optical photons to optimize the placement of the PMTs cosq

14. top m-veto PMT Water tank “Ring” “Pillbox” VM2000 Optimization of Cerenkov veto (2) Configurations with 72 and 78 PMTs are being explored. Crytical regions: neck and bottom of cryovessel Optical photons tracked within the MaGe framework. CPU-intensive but works ok. It also works with LAr scintillation and WLS