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

13 September, 2007Geant4 Workshop – Hebden Bridge Search for neutrinoless  decay of 76 Ge 0  : (A,Z)  (A,Z+2) + 2e - Neutrinoless 2  -decay violates the lepton number conservation: ΔL=2 76 Ge 76 Se Q  = 2039 keV Explore the Dirac/Majorana nature of neutrino and the absolute mass scale Very rare process: T 1/2 > y New generation experiments require unprecedented low- background conditions and large masses! Two experiments with 76 Ge, 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-scale 76 Ge experiment

13 September, 2007Geant4 Workshop – Hebden Bridge 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 1.To provide a physics simulation package to aid in the optimal design, operation and analysis of data. 2.It must persist over the long lifetime of the experiments. 3.It must be well-maintained, documented, and robust. 4.Maintain record of results. functionality OO and abstraction capabilities of C++ and STL for flexibility 1.Energy deposition of particles from radioactive sources, cosmic rays, and signal sources. 2.Pulse-shape formation in crystals, different segmentation schemes, and crystal geometries. 3.Electronics. 4.Shielding (neutron absorption and muon tagging). 5.Radioactive decay chains and emissions. 6.Signal: double-beta decay 7.Activation in detector material. physics Geant4 meets all physics requirements, has OO structure, well established MaGe framework

13 September, 2007Geant4 Workshop – Hebden Bridge What’s MaGe ? MaGe is a Geant4-based Monte Carlo simulation package dedicated to experiments searching for 0 2  decay of 76 Ge (and low-background experiments in general). It is developed jointly by the Majorana and GERDA simulation groups Idea: to share a common simulation framework with an abstract set of interfaces, while each experiment adds its concrete implementations (geometry, output, etc...). No constraints to both sides (geometry, physics, etc.)  each component can be independently re-written The whole package can be configured and tuned by macros without accessing the code  accessible to new users and non experts of C++

13 September, 2007Geant4 Workshop – Hebden Bridge MaGe block structure Takes care of all common parts that are not experiment- specific MJ outputGERDA output Event generators, description of physics processes, properties of the materials, management Majorana geometry GERDA geometry MaGe The common CVS repository allows easy and parallel development of the code (Geant4 philosophy) tunable and customizable by macro Different formats supported (AIDA interfaces, ROOT, ASCII-based)

13 September, 2007Geant4 Workshop – Hebden Bridge Why to develop MaGe ? Basic documentation available, paper in preparation avoids duplication of the work for the common parts of the simulations (generators, physics, materials, management) can provide the complete simulation 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 script and is flexible for experiment-specific implementation of geometry and output is suitable for the distributed development

13 September, 2007Geant4 Workshop – Hebden Bridge Some common tools in MaGe Generators Radioactive isotopes and 2  Cosmic ray muons Neutrons  beam Pencil beams Selectable by macro General-purpose samplers Random sampling of the primary position uniformly within an arbitrary volume or surface (even of complex shape)

13 September, 2007Geant4 Workshop – Hebden Bridge A MaGe/GERDA applications Top muon veto Neck Cryostat Water Water tank Detector array GERDA geometry in MaGe 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

13 September, 2007Geant4 Workshop – Hebden Bridge MaGe/Geant4 validation for  -rays - I MaGe results compared with test-stand experimental data 18-fold segmented n-type detector (Canberra-France) mass: 1.6 kg height: 70 mm radii: 10 and 70 mm 6 segments in  3 segments in z Max-Planck-Institut für Physik, Munich Detector irradiated with radioactive sources

13 September, 2007Geant4 Workshop – Hebden Bridge MaGe/Geant4 validation for  -rays - II 60 Co source: data, MC, background Core electrode energy spectrumOccupancy of each segment substructure average deviation ~5% Substructure effect is reproduced in MaGe using an effective model for drift anisotropy. DAQ efficiency also included nucl-ex/ v1

13 September, 2007Geant4 Workshop – Hebden Bridge MaGe/Geant4 validation for  -rays - III SF L  ratio between all events in a given peak and the single- segment ones only single-segment (=localized) events are background for neutrinoless  decay Different  -energy from radioactive sources taken into account  good agreement with MaGe nucl-ex/ v1

13 September, 2007Geant4 Workshop – Hebden Bridge MaGe/Geant4 validation for  -rays - IV 137 Cs : single  line at 662 keV w/o LAr veto w/ LAr veto Data taken at MPIK- Heidelberg: Ge crystal immersed in liquid argon Very good agreement with MaGe for 137 Cs (spectrum and absolute rates)

13 September, 2007Geant4 Workshop – Hebden Bridge Simulation of low-energy neutrons - I AmBe source neutron Paraffin collimatorDetector GERDA and Majorana have irradiated test Ge detectors with neutron sources.  - rays produced by inelastic scattering and radiative capture Majorana setup 4.4 MeV  from Am-Be source p(n,d) 

13 September, 2007Geant4 Workshop – Hebden Bridge 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  -rays) Data MaGe + background background 175 keV 71m Ge 140 keV 75m Ge 198 keV 71m Ge The simulation has spurious and missing peaks (mainly related to metastable Ge states) Data MaGe

13 September, 2007Geant4 Workshop – Hebden Bridge Radioactive contaminations - I Cold Plate 1.1 kg Crystal Thermal Shroud Vacuum jacket Cold Finger Bottom Closure MaGe has been used for the finalization of the Majorana reference design: estimate of background from different sources and radiopurity requirements on detector components Several radioactive isotopes and detector components have been considered (2 TB of data produced)

13 September, 2007Geant4 Workshop – Hebden Bridge Radioactive contamination - II Experiment MaGe Crystal 1x8 4x8 Counts / keV / 10 6 decays Different segmentation schemes tested for different radioactive sources Segmentation successfully rejects background. Good agreement data vs. MC 60 Co

13 September, 2007Geant4 Workshop – Hebden Bridge Surface  contaminations MaGe used to estimate background due to surface  contamination in the crystals from natural radioactivity Example spectrum in Majorana Reference Design ( 222 Rn to 206 Pb)

13 September, 2007Geant4 Workshop – Hebden Bridge 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 Generator MaGe x, y, z, t, dE Pulse shape simulation x, y, z, t, dE Any other MC Common interface defined (MGDO)

13 September, 2007Geant4 Workshop – Hebden Bridge Conclusions Two experiments, Majorana and GERDA, will look for 0  decay of 76 Ge, 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 with test stand data (  MaGe and Geant4 validation)  -rays and low-energy neutrons Interface with pulse shape generators in progress

13 September, 2007Geant4 Workshop – Hebden Bridge 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