1. TG10 status report L. Pandola INFN, Gran Sasso National Laboratories for the TG10 Task Group Gerda Collaboration Meeting, Tuebingen November 9th – 11th, 2005

2. MaGe: what’s in the common part? Generators Radioactive isotopes and 2  PNNLiso RDMiso decay0 Cosmic ray muons cosmicrays musun Neutrons AmBe wangneutrons neutronsGS  beam General TUNLFEL G4gun SPS

3. MaGe:physics list EM physics Hadronic physics Optical physics Cut realms Standard package QGSP_BIN_ISO list from M. Bauer. Optimized for DM and for  -induced neutron production * Off On Different cuts selectable according to application (e.g. for CR they are more relaxed). Cuts can be different in different regions of the set-up Default list Low Energy package: includes fluorescence and atomic effects * [M.Bauer, Proc. of V Inter. Workshop on the Identification of DM]

4. top  -veto water tank lead shielding cryo vessel neck Ge array MaGe: the Gerda-specific part Gerda main geometry and test stands LArGe set-up at MPIK PMT crystal reflector and WLS tank LArGe set-up at GS

5. Muons crossing the detector Phase I: 9 Ge crystals (total mass: 19 kg). Energy threshold: 50 keV Energy spectrum without and with the crystals anti- coincidence (1.5  2.5 MeV): 2.1·10 -3 counts/keV kg y background reduction of a factor of 3-4 No cuts2.1 · 10 -3 (cts/keV kg y) Crystals anci-coincidence6.4 · 10 -4 Anti-coincidence+ top  -veto (plastic scint)5.4 · 10 -4 Cerenkov  -veto< 3 · 10 -5 (95% CL) 6.2 years annihilation peak Energy (MeV) Physics list dependence < 25%. Total systematics ~ 35%

6. Radioactive contaminations Analysis: Anti-coincidence between detector and segments (Phase II detectors), energy cut MaGe is used for detailed Monte Carlo simulation of contaminations in the inner parts of detector Components: Natural decay chains of 238 U and 232 Th (assuming broken equilibrium) Surface contamination with 210 Pb Cosmogenically produced isotopes 68 Ge and 60 Co Studies performed in Munich

7. Conclusions A common dedicated MaGe poster was presented at the TAUP in Zaragoza: contribution in the Proceedings A large variety of applications has been succesfully performed with MaGe: cosmic rays, neutrons, radioactive contaminants, optical photons (including WLS) First consistency check of hadronic physics with FLUKA ( 16 N in water), in addition to the existing work! Validation of EM physics with radioactive sources ( 60 Co and 133 Ba with the existing detectors) at GS and Hd The development of the MaGe framework is ongoing regularly  mutual benefit (debugging, extensions) Draft of a TG10 paper concerning  -induced background

8. Muons crossing the detector Phase I: 9 Ge crystals (total mass: 19 kg). Energy threshold: 50 keV Energy spectrum without and with the crystals anti- coincidence (1.5  2.5 MeV): 2.1·10 -3 counts/keV kg y background reduction of a factor of 3-4 No cuts2.1 · 10 -3 (cts/keV kg y) Crystals anci-coincidence6.4 · 10 -4 Anti-coincidence+ top  -veto (plastic scint)5.4 · 10 -4 Cerenkov  -veto< 3 · 10 -5 (95% CL) 6.2 years annihilation peak Energy (MeV) Physics list dependence < 25%. Total systematics ~ 35%

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

10. distance from track (m) Gerda water tank radius Muons interacting in the rock Water and nitrogen are effective neutron moderators Conservative estimate: the distance  -n is = 0.6 m (from LVD)  good chances that neutrons in the crystal are accompained by the primary  in the water (veto is effective!) Estimate the contribution from high-energy neutrons produced in the surrounding rock by cosmic ray  ’s Spectrum and total flux (~ 300 n/m 2 y) 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

11. Mu-induced activation Muon-induced interactions can create long-lived (> ms) unstable isotopes in the set-up materials with Q > Q  Isotopes in LN 2 ( 12 B, 13 N, 16 N), copper ( 60 Co, 62 Cu) and water ( 16 N, 14 O, 12 B, 6 He, 13 B) give contributions below 10 -6 cts/keV kg y Notice: 16 N production rate in water is in good agreement with FLUKA (& data from SK) [hep-ph/0504227]  good MC cross-check cannot be vetoed or shielded against Isotopes in the crystals are relevant (detected with high- efficiency). From the MC  6· 10 -5 cts/keV kg y 74 Ga8.1 m<0.08 ev/kg y 69 Ge39 h<0.05 ev/kg y 75 Ga2 m0.09 ev/kg y 77 Ge11 h<0.02 ev/kg y 76 Ga33 s0.06 ev/kg y 71 Ge and 75 Ge not dangerous  - and  - capture n capture,  inelastic

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

13. Materials & masses in Phase II set-up PartMaterialMass [g] CrystalGermanium2400 (per detector) HolderCopper Teflon 31 (per holder) 7 (per holder) CableCopper Kapton Copper Nickel Gold Aluminum 1.3 (per cable) 0.8 (per cable) 0.04 (per detector) 5.6·10 -4 (per detector) 8.2·10 -4 (per detector) Support stringsCopper10 (per string) Electronicsmisc (mixture)100 (per set)

14. Measured activities in materials MaterialContamination Copper (from LENS)≤ 16 μBq/kg ≤ 19 μBq/kg ≤ 10 μBq/kg Ra-226 Th-228 Co-60 Teflon≤ 160 μBq/kg Ra-226 Th-228 Kapton~ 2 mBq/kg [1] Ra-226, Th-228, Co-60 Enr. Germanium≤ 0.1 μBq/kg 145 atoms/kg 40 atoms/kg 0.63 μBq/surface 0.13 μBq/surface Ra-226 Th-228 Ge-68 Co-60 Pb-210 Th-232 Electronics10 mBq/kg [1] Ra-226, Th-228 [1] estimate!

15. Background estimation PartBkgRate [10 -3 cnts/kg/keV/y] Events [cnts/y] [1] CrystalU-238 Th-232 Co-60 Ge-68 Pb-210 (s) Th-232 (s) 0.25 0.05 0.03 1.53 0.13 0.17 0.25 0.05 0.03 1.55 0.13 0.17 Holderall (copper) all (Teflon) 0.12 0.17 0.12 0.17 Cablesall (copper) all (Kapton) 0.02 1.31 0.02 1.34 Electronicsall23.6523.84 Sum~27 [1] 20 keV window

16. 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 (  -produced and from radioactivity)

17. Simulation of LArGe setup at MPIK Simulation of LArGe integrated in the MaGe framework Simplified toy-geometry Goal: 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

18. 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

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

20. 34 p.e. (60% WLS QE) Measurement with collimated 57 Co LArGe setup irradiated with external collimated 57 Co 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)

21. Optimization of Cerenkov veto Assumptions on Cerekov veto threshold: 120 MeV (~60 cm) 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 neck minimum GS coverage Pb plate shadow Input angular spectrum cos 

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