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Activity report of TG10

Activity report of TG10. (simulations and background studies). L. Pandola (LNGS) for the TG10 group. Gerda Collaboration Meeting, February 3-5, 2005. The Task Group 10. Goals:. evaluation of the background index. optimization of Gerda detector and data analysis.

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Activity report of TG10

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  1. Activity report of TG10 (simulations and background studies) L. Pandola (LNGS) for the TG10 group Gerda Collaboration Meeting, February 3-5, 2005

  2. The Task Group 10 Goals: evaluation of the background index optimization of Gerda detector and data analysis sensitivity to 0n2b signal Simulation of signal and backgrounds in the Gerda detector Geant4-based MaGe framework in collaboration with Majorana Validation and cross-check Pulse shape, segmentation, mirror charges, etc. With TG9: definition of data format including Who: LNGS, Munich, Russian groups, MPIK http://wwwgerda.mppmu.mpg.de/MC/monte_carlo.html

  3. The MaGe framework Mid-October 2004: Gerda & Majorana joint MC workshop Idea: collaboration of the two MC groups for the development of a common framework based on Geant4 abstract set of interfaces: each experiment has its own concrete implementation 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;   suitable for the distributed development

  4. Report: wwwgerda.mppmu.mpg.de/MC/gerda_monte_pic/gerda.pdf The MaGe framework Majorana already had a working framework, (kindly supplied by the MC group) evaluated and found suitable for Gerda needs and for joint development Warning: To have a common framework simply means sharing the same generic interfaces. No contraints to the Gerda side (geometry, physics, etc.)  each component can be independently re-written Present situation: Common CVS repository hosted at Munich Discussion forum hosted at Berkeley

  5. mjgeometry mjio Generator, physics processes, material, management, etc. gerdageometry gerdaio The MaGe structure Each group has its own geometry setup and corresponding output, everything else can be shared. To run a new simulation:  write only your geometry and your output  register them in the management classes Can be downloaded from the CVS repository in Munich setup instructions at: wwwgerda.mppmu.mpg.de/MC/monte_carlo_pic/setup.ps

  6. Activity for the common part Development of generic (not Gerda-specific) tools  Optimization and modularization of the framework  Interface to the decay0 generator by V.I. Tretyak 0n2b signal according to several theoretical models  Random sampling of points uniformly from a specified (generic) volume  Generator for cosmic ray muons  Access to the trajectories of all the secondaries All this work would have been duplicated ...

  7. Activity for the Gerda-specific part 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

  8. Gerda MC Geometry New OO structure of geometry classes Flexible executable: set of commands to configure geometryNumber of columns and orientation, segmentation of crystals, support structure/shielding on/off, etc. 10 columns segmented crystals (6x3) standard geometry Kevin Kröninger - MPI München

  9. Activity for the Gerda-specific part Output: Class to create a ROOT TTree with all the interesting information (energy deposition and position of hits in Ge, Liquid N2, water, etc.) ready to be interfaced with software for the simulation of pulse shape  Munich Generic AIDA interface for other analysis tools (e.g. HBOOK) Physics studies in progress: background induced by cosmic ray muons and neutrons g background in electronics and support segmentation effect for background and 0n2b signal external g background and shielding requirements

  10. Two examples of macros /MG/geometry/detector GerdaArray /MG/geometry/database false /MG/geometry/detector/crystal/truecoaxial false /MG/geometry/detector/general/numcol 3 /MG/geometry/detector/general/crypercol 3 /MG/geometry/detector/crystal/height 8.5 cm /MG/generator/select cosmicrays /MG/eventaction/rootschema GerdaArray /MG/geometry/detector GerdaArray /MG/geometry/database false /MG/geometry/general/constructshield false /MG/generator/select decay0 /MG/eventaction/rootschema GerdaArray /MG/generator/confine volume /MG/generator/volume Ge_det_0 /MG/generator/decay0/filename myfile.dat Generates cosmic ray events in a 3x3 array of non-coaxial crystals in the Gerda shielding Generates events uniformly in the volume of a Ge crystal (without shielding). Kinematic read from a decay0 file Geometry, tracking cuts, generator and output pattern  selectable and tunable via macros No need to recompile, easy to use for non-expert people

  11. Small flux, small Ge volume: 59 events/kg y Cosmic ray muons (Phase I) Flux at Gran Sasso: 1.1 m/m2 h (270 GeV) ~ 60 – 70 events/kg y in H-M Further reduced by anti-coincidence with other Ge-crystals and with top (or Cerenkov) m-veto Input energy spectrum from Lipari and Stanev, Phys. Rev. D 44 (1991) 3543 Input angular spectrum uniform in  first approximation in  Energy (keV)

  12. Cosmic ray muons (Phase I) 9 Ge crystals for a total mass of 19 kg; threshold: 50 keV Sum spectrum annihilation peak 3.93 years 149 counts in 1500  2500 keV 21 counts in 2000  2100 keV Energy (MeV) (1.5  2.5 MeV): 2·10-3 counts/keV kg y single-Ge (~4·10-3 counts/keV kg y in H-M simul.) C. Doerr, NIM A 513 (2003) 596 1.5 MeV 2.5 MeV Number of hit detectors multi-hit: 35.2% below threshold Energy (MeV)

  13. Ge and top m-veto anti-coincidence (suppression factor: ~20) Cosmic ray muons (Phase I) Sum spectrum Ge anti-coincidence (suppression factor: ~2) 3.93 years Energy (MeV) Threshold for plastic scintillator (top m-veto): 1 MeV ~ 4 events/kg y Energy (MeV)

  14. Cosmic ray muons (Phase I) Background substantially lower than previously estimated Instrumentation of water as a Cerenkov m-veto is an open issue for the Collaboration ( redundancy)

  15. Cosmic ray muons (Phase I) Correlated issue: production of short-lived radioactive isotopes induced by the muon showers delayed energy deposition Most dangerous isotopes (g above Qbb): Production in dangerous isotopes in nitrogen is much smaller Background index not evaluated yet  probably negligible Cross-check of isotope production with independent codes (e.g. FLUKA) would be very welcome

  16. Cosmogenic neutrons (muon interaction in the rock) small flux (200 n/m2y), hard energy spectrum (up to tens of GeV) Energy and angular spectrum from H. Wulandari et al. hep-ex/0401032 Negligible in Gerda: < 3.8 · 10-5cts/keV kg y (95% CL) with Ge-anticoincidence Neutrons from fission and (a,n) soft energy spectrum (up to 8 MeV), higher flux (20 n/m2 h) Neutrons (Phase I) Work in progress. Difficult to simulate because CPU-intensive 0.05% of the events deposit energy the nitrogen volume  90 ev/m2 y Probably not an issue. g from n+p shielded by LN2 In H-M: 3 · 10-3 cts/keV kg y (without water shielding) ! C. Doerr, NIM A 513 (2003) 596 To do next: validation of the simulation with data and cross-check with independent codes

  17. No cuts: < 1.2· 10-4cts/keV kg y (95%) Ge-anticoincidence: < 8 · 10-5cts/keV kg y (95%) Ge and Cerenkov m-veto: < 4 · 10-5cts/keV kg y (95%) CNGS muons Flux at Gran Sasso: 0.86 m/m2 d (<E> ~ 15 GeV) LVD Collaboration, hep-ex/0304018 30 times smaller than cosmic ray flux and softer spectrum Top m-veto uneffective: only Ge-anticoin. and water m-veto Not evaluated yet in detail Rough estimate (15-GeV m): LVD Collaboration, hep-ex/0304018 Not a critical issue

  18. Signal and background studies Example: 60Co Photons carry energy to more than one crystal/segment (multiple-site) Cut on the number of hit crystals or segments reduces 60Co events to 19% (6%) ~19% ~6% Kevin Kröninger - MPI München Hit crystals Hit segments

  19. Signal and background studies Background suppression efficiency: Segmentation: 6 (phi) x 3 (z) Threshold: 10 keV; Energy window: Qbb ± 5 keV Pulse shape analysis and pattern recognition not included Kevin Kröninger - MPI München

  20. Maintenance of a common CVS server for MaGe  Background and signal studies/background suppression Segmentation studies  Update of geometry: crystals and support structure Future tasks: Pulse shape analysis (incl. MC) Test facility for Ge-crystals (incl. MC) MPI Munich MC activities Kevin Kröninger - MPI München

  21. direct simulation of g transportation signal window: 1800  2300 keV 6.6 · 10-6c/keV kg y Water shielding: 300 cm in the cylindrical part 1-2 · 10-4c/keV kg y 200 cm above and below Other background calculations Background from inner tank envelope: Cu: 25 · 10-6 Bq/kg of 232Th Fe: 20 · 10-3 Bq/kg of 232Th 10-3 c/kg keV y guaranteed With 50-cm-below position, Fe negligible Background from external gammas: detector placed 50 cm below center intensity of 2.6 MeV: 0.0625 cm-2s-1 A. Klimenko – INR, ITEP, Dubna, MPIK

  22. upper part cylindrical part lower part bottom part: 7 cm of Pb upper part: 6 cm of Pb cylindrical part: no further shielding needed neck: 15 cm of Pb Cu tank: LAr is required Other background calculations To go lower than 10-5 c/keV kg y: A. Klimenko – INR, ITEP, Dubna, MPIK

  23. Backgrounds, segmentation, pulse shape (via interface) Precise description of Gerda setup and shielding   Estimation of external g background and shielding First results of signal and bck in crystals & cables Conclusions  MC package MaGe ready for Gerda & Majorana groups Downloadable from CVS, flexible and runnable by macro  Structure complete and ready for physics studies  Preliminary results of m-induced and n background Top m-veto enough for background of a few ·10-4 c/kg keV y Neutrons, CNGS and isotopes production presumably not critical 10-4 c/kg keV achievable with present shielding, 10-5needs LAr 3-month activity and still a lot of work to do in the future... ...Well begun is half done !

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