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MaGe: a Monte Carlo framework for the GERDA and Majorana experiments

MaGe: a Monte Carlo framework for the GERDA and Majorana experiments. Luciano Pandola INFN, Laboratori Nazionali del Gran Sasso for the MaGe development group Geant4 Workshop Hebden Bridge, UK 13 September 2007. 76 Se. 76 Ge. Q bb = 2039 keV.

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MaGe: a Monte Carlo framework for the GERDA and Majorana experiments

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  1. MaGe: a Monte Carlo framework for the GERDA and Majorana experiments Luciano Pandola INFN, Laboratori Nazionali del Gran Sasso for the MaGe development group Geant4 Workshop Hebden Bridge, UK 13 September 2007

  2. 76Se 76Ge Qbb = 2039 keV Explore theDirac/Majorana natureof neutrino and the absolutemass scale Very rare process: T1/2 > 1025 y New generation experiments require unprecedented low-background conditions and large masses! Two experiments with 76Ge, GERDA (Europe-Russia) and Majorana (US-Japan) have been proposed for next generation (100 kg scale). They will explore the feasibility of a world-wide ton-scale76Ge experiment Search for neutrinoless bb decay of 76Ge 0:(A,Z)  (A,Z+2) + 2e- Neutrinoless 2b-decay violates the lepton number conservation: ΔL=2 Geant4 Workshop – Hebden Bridge

  3. Energy deposition of particles from radioactive sources, cosmic rays, and signal sources. Pulse-shape formation in crystals, different segmentation schemes, and crystal geometries. Electronics. Shielding (neutron absorption and muon tagging). Radioactive decay chains and emissions. Signal: double-beta decay Activation in detector material. functionality physics To provide a physics simulation package to aid in the optimal design, operation and analysis of data. It must persist over the long lifetime of the experiments. It must be well-maintained, documented, and robust. Maintain record of results. Geant4 meets all physics requirements, has OO structure, well established OO and abstraction capabilities of C++ and STL for flexibility MaGe framework Common issues in Monte Carlo’s GERDA and Majorana have very similar requirements and issues in terms of Monte Carlo simulations for background and sensitivity studies Geant4 Workshop – Hebden Bridge

  4. Idea: to share a common simulation framework with an abstract set of interfaces, while each experiment adds its concrete implementations (geometry, output, etc...). The whole package can be configured and tuned by macroswithout accessing the code accessible to new users and non experts of C++ No constraints to both sides (geometry, physics, etc.)  each component can be independently re-written What’s MaGe ? MaGe is a Geant4-based Monte Carlo simulation package dedicated to experiments searching for 0n2b decay of 76Ge (and low-background experiments in general). It is developed jointly by the Majorana and GERDA simulation groups Geant4 Workshop – Hebden Bridge

  5. Majorana geometry GERDA geometry Event generators, description of physics processes, properties of the materials, management MaGe block structure MaGe Takes care of all common parts that are not experiment-specific tunable and customizable by macro MJ output GERDA output Different formats supported (AIDA interfaces, ROOT, ASCII-based) The common CVS repository allows easy and parallel development of the code (Geant4 philosophy) Geant4 Workshop – Hebden Bridge

  6. Why to develop MaGe ? • avoidsduplication of the work for the common parts of the simulations (generators, physics, materials, management) • can provide the completesimulation chain (including pulse shape) • allows a more extensive validation of the simulation with experimental data coming from both experiments  also Geant4 validation Why MaGe? • can be run by scriptandisflexible for experiment-specific implementation of geometry and output • is suitable for the distributed development Basic documentation available, paper in preparation Geant4 Workshop – Hebden Bridge

  7. Generators General-purpose samplers Random sampling of the primary position uniformly within an arbitrary volume or surface (even of complex shape) Some common tools in MaGe Radioactive isotopes and 2b Cosmic ray muons Pencil beams Neutrons g beam Selectable by macro Geant4 Workshop – Hebden Bridge

  8. MaGe widely used for background and sensitivity studies in GERDA, and for design optimization cosmic ray muons maximum tolerable radioactivity for detector parts efficiency of multiplicity cuts neutrons NIM A 570 (2007) 149 several GERDA notes NIM A 570 (2007) 479 in preparation A MaGe/GERDA applications GERDA geometry in MaGe Top muon veto Neck Water tank Water Cryostat Detector array Geant4 Workshop – Hebden Bridge

  9. MaGe/Geant4 validation for g-rays - I MaGe results compared with test-stand experimental data 18-fold segmentedn-type detector (Canberra-France) Max-Planck-Institut für Physik, Munich mass: 1.6 kg height: 70 mm radii: 10 and 70 mm 6 segments in  3 segments in z Detector irradiated with radioactive sources Geant4 Workshop – Hebden Bridge

  10. substructure average deviation ~5% Core electrode energy spectrum Occupancy of each segment MaGe/Geant4 validation for g-rays - II 60Co source: data, MC, background Substructure effect is reproduced in MaGe using an effective model for drift anisotropy.DAQ efficiency also included nucl-ex/0701005v1 Geant4 Workshop – Hebden Bridge

  11. MaGe/Geant4 validation for g-rays - III SFL ratio between all events in a given peak and the single-segment ones nucl-ex/0701005v1 only single-segment (=localized) events are background for neutrinoless bb decay Different g-energy from radioactive sources taken into account  good agreement with MaGe Geant4 Workshop – Hebden Bridge

  12. MaGe/Geant4 validation for g-rays - IV 137Cs : single  line at 662 keV Data taken at MPIK-Heidelberg: Ge crystal immersed in liquid argon w/o LAr veto Very good agreement with MaGe for 137Cs (spectrum and absolute rates) w/ LAr veto Geant4 Workshop – Hebden Bridge

  13. Detector Paraffin collimator neutron AmBe source p(n,d)g 4.4 MeV  from Am-Be source Simulation of low-energy neutrons - I GERDA and Majorana have irradiated test Ge detectors with neutron sources. g-rays produced by inelastic scattering and radiative capture Majorana setup Geant4 Workshop – Hebden Bridge

  14. Data MaGe + background background The simulation has spurious and missing peaks (mainly related to metastable Ge states) Data MaGe 140 keV 75mGe 175 keV 71mGe 198 keV 71mGe Simulation of low-energy neutrons - II The general spectral shape is reproduced fairly well Additional problem: proper description of the primary AmBe spectrum (neutrons and g-rays) Geant4 Workshop – Hebden Bridge

  15. Radioactive contaminations - I MaGe has been used for the finalization of the Majorana reference design: estimate of background from different sources and radiopurity requirements on detector components Vacuum jacket Cold Plate Cold Finger 1.1 kg Crystal Thermal Shroud Bottom Closure Several radioactive isotopes and detector components have been considered (2 TB of data produced) Geant4 Workshop – Hebden Bridge

  16. Radioactive contamination - II Different segmentation schemes tested for different radioactive sources Segmentation successfully rejects background. Good agreement data vs. MC Crystal 60Co 1x8 4x8 Experiment Counts / keV / 106 decays MaGe Geant4 Workshop – Hebden Bridge

  17. Surface a contaminations MaGe used to estimate background due to surface a contamination in the crystals from natural radioactivity Example spectrum in Majorana Reference Design (222Rn to 206Pb) Geant4 Workshop – Hebden Bridge

  18. Common interface defined (MGDO) Pulse shape simulation MaGe Generator x, y, z, t, dE Any other MC x, y, z, t, dE Ongoing development: pulse shape A (modular) software for the simulation of pulse shapes is under joint development. It can be used in conjunction with MaGe, providing the whole chain from event generation, propagation to pulse simulation Advantages of running with MaGe is the flexibility and existing software infrastructure (e.g. geometry, I/O). PS simulation can be interfaced with any other MC. Different PS implementations are possible Geant4 Workshop – Hebden Bridge

  19. Conclusions • Two experiments, Majorana and GERDA, will look for 0nbb decay of 76Ge, with different designs • They have similar issues and requirements for MC simulation • The MC groups are jointly developing since 2004 a Geant4-based and OO Monte Carlo framework called MaGe • Geant4 well established in physics, has flexible OO interfaces • avoids duplication of work, easy to develop and mantain • can be validated and tested more deeply and precisely • includes general-purpose tools (generators, samplers) • easy to use by macro (also for non-experts) • Used for several applications and background studies • Simulation results compared withtest stand data ( MaGe and Geant4 validation) • g-rays and low-energy neutrons • Interface with pulse shape generators in progress Geant4 Workshop – Hebden Bridge

  20. Two examples of macros /MG/geometry/detector MJRDBasicShield /MG/geometry/idealCoax/setDefaults /MG/geometry/idealCoax/deadLayerOn true /MG/geometry/idealCoax/outerDeadLayer 1 micrometer /MG/generator/select cosmicrays /MG/eventaction/rootschema MCEvent /MG/geometry/detector GerdaArray /MG/geometry/database 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 single coaxial crystal in the Majorana setup. Crystal parameters are customized Generates events uniformly in the volume of one Ge crystal in the GERDA array. Kinematics read from an external file Geometry, tracking cuts, generator and output pattern  selectable and tunable via macros (same executable) No need to recompile, easy to use for non-expert people Geant4 Workshop – Hebden Bridge

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