Luciano Pandola INFN Gran Sasso Valencia, April 14 th , 2005

1. Geant4 and the underground physics community Luciano Pandola INFN Gran Sasso Valencia, April 14th, 2005

2. What is ? • OO Toolkit for the simulation of the interaction of particles with matter • physics processes (EM, hadronic, optical) cover a comprehensive set of particles, materials and over a wide energy range • it offers a complete set of functionalities (tracking, geometry, hits) • born for the HEP community, but extensively used also in medical physics, astroparticle physics and space applications • It is also an experiment of distributed software production and management, as alarge international Collaborationwith the participation of various experiments, labs and institutes • Has been creating exploiting a rigorous software engineering and Object Oriented technologies, implemented in the flexible C++ language

3. Where does it come from? • Very high statistics to be simulated • robustness and reliability for large scale production • Exchange of CAD detector descriptions • very complex geometries and experimental setups • Transparent physics for experimental validation • possibility to use alternative/personalized physics models • Physics extensions to high energies • LHC, cosmic ray experiments • Physics extensions to low energies • space science, astrophysics, medical physics, astroparticle physics

4. Uniform treatment of electromagnetic and hadronic processes Abstract interface to physics processes Tracking independent from physics Distinction between processes and models Often multiple models for the same physics process (complementary/alternative) Users can choose those that best match their needs (energy range, precision vs. CPU time) Open system Users can easily create and use their own models Transparency Calculation of cross-sections independent from the way they are accessed (data files, analytical formulae etc.) Distinction between the calculation of cross sections and their use Calculation of the final state independent from tracking Physics

5. Physics class structure Only production cuts for e- and g’s are used all particles tracked until they stop Advantages: very flexible, multiple alternative (user-defined) models Drawback: difficult to choose the most suitable process (some lack of documentation, exp. for hadronic models)  black box approach

6. 180 GeV μ 800 Events/10 nA 700 600 500 400 300 200 Calorimeter Signal [nA] 100 0 400 -100 0 100 200 300 500 User requirements & validation Geant4 is open to user requirements concerning new capabilities and physics models http://pcitapiww.cern.ch/asd/cgi-bin/geant4/urd/ • Problems: • manpower (usually short) • specific expertise needed • modular development (some groups are more active than others)... Geant4 was born at CERN so it was mainly “tuned” and developed by people working in the accelerator groups well-established MC, validation from test-beams of the experiments

7. Geant4-05-00 e.m. Physics 15x15 cm2 Differences 15x15 cm2 User requirements & validation Geant4 became a well-established “reference” Monte Carlo also in other sectors medical physics Bragg-peak of 60-MeV protons for cancer therapy Depth dose and profile curves for clinical x-ray beams Require accuracy of EM processes (LowE)

8. Physics Validation • Systematic and extensive validation of the whole physics content is fundamental in Geant4 • Specific validations at different levels necessary stage to guarantee reliable simulations • Microscopic physics validation of each model •  cross section, angular/energy distributions • Macroscopic validation with experimental use cases •  full simulation of experimental set-ups The results of simulations must be quantitatively compared with established and authoritative reference data experimental measurements on refereed journals and/or open standard dabatases (ICRU, NIST, Livermore)

9. Data: Shimizu et al, Appl. Phys. 9 (1976) 101 320 nm Al slab E = 20 keV G4 LowE NIST 1040 nm G4Standard G4 LowE User requirements & validation Geant4 EM physics models (“standard” and “low energy”) are being validated in a systematic and quantitative way K. Amako et al., Validation of Geant4 electromagnetic physics versus the NIST databases, submitted to IEEE Trans. Nucl. Scie. photon attenuation electron backscattering electron transmission Data

10. User requirements & validation (My feeling) Geant4 is still not considered a fully established and trustworthy Monte Carlo in the underground physics community • small overlap between the Collaboration and the experiments ( = 3) • no test-beams available, so validation much more complicated • requires extensions to High Energy (e.g. muons) and to Low Energy (e.g. fluorescence)  typically “decoupled” in the modular development of Geant4 The medium-term goal of the G4 Collaboration is to improve this situation, consistently with the available manpower. Effort for a more complete validation plan (what are the priorities?). Needs strong connection with experimental and MC groups of the experiments (= us), also for providing data!

11. What do we need ? (my collection...) • High energy muons interactions & showers: • neutron and hadron production (critical for DM experiments) • isotope production has ever been validated or cross-checked? • Low energy electromagnetic extensions: • precise tracking of low-energy leptons and hadrons • more precise energy and angular spectra • atomic de-excitation (e.g. fluorescence x-rays)    • Other: • very precise decay schemes for Radioactive decay (low-branching channels) • EC decay (with fluorescence) Other decays (e.g. spont. fission)   

12. The whole physics content of the Penelope Monte Carlo code has been re-engineered into Geant4 shell effects processes for photons: release 5.2, for electrons: release 6.0 • New complete set of alternative and dedicated low energy EM physics models (atomic effects included) Attenuation coeff. (cm2/g) NIST data Penelope Low energy EM extensions Geant4 provides dedicatedLow Energy EM models electrons, positrons and gammas down to 250 eV Based on EPDL97, EEDL and EADL evaluated data libraries neutrino/dark matter experiments, space and medical applications Possible thanks to the OO-oriented technology used in Geant4 Hadron, anti-proton and ionmodels

13. A few examples of applications... Double beta decay 76Ge experiment (GERDA & Majorana): OO toolkit based on Geant4 (MaGe) Flexible enough to allow common parts (e.g. generators, physics, other tools)  not duplicated experiment-specific parts (geometry, i/o) Preliminary physics studies: gbackground from outside and from structures (ropes, contact) efficiency of segmentation/anticoincidence background from cosmic ray muons

14. A few examples of applications... Preliminary results: Goal 10-3-10-4 counts/keV·kg·y @ Qbb Achievable for g and cosmic ray m (with dedicated veto): Cosmic ray muons mainly from EM showers  physics reliable 76Ge 0n2b region Fission, (a,n) and cosmogenic neutrons are not an issue (very different for DM expts) physics reliable? (with the proper physics list)  work in progress from DM groups Isotope production not an issue reliability unknown  we plan to cross-check with Fluka

15. simulation simulation sample detector data data source A few examples of applications... Small (stupid) application derived from studies of environmental radioactivity from rocks and sands Geant4 (LowE EM) can reproduce very well the results of a calibration with a 60Co source (in presence of the sample) it works very well in this regime

16. A few examples of applications... Dark matter experiment (ZEPLIN 3): Code from A. Howard and H. Araujo. Released as an advanced example of Geant4

17. A few examples of applications... Experiment backgrounds internal detector radioactivity rock radioactivity m-induced neutron production shielding and veto systems G4 is uniquely suited forintegratedsimulations of Dark Matter detectors Detector response Scintillation Ionisation (thermal) Optics Photon generation Light collection studies Simulated Data Visualisation Run-time analysis Input to data analysis software Calibration Neutrons Gammas

18. A few examples of applications... • Ionisation extraction • Drift in liquid xenon • Extraction to gas • Drift in gas • Luminescence light Electric fields Light collection maps

19. Our priorities for validation Suggestions from Prague meeting forwarded to the G4 Collaboration • Production of m-induced neutrons in high-Z materials • Propagation of Low Energy neutrons (up to a few MeV) • Inelastic scattering of neutrons • Interactions of high-energy muons • Isotope production comparison with FLUKA, experimental data comparison with MCNP, experimental data comparison with other codes t.b.d. Validation is this field is a difficult task close collaboration required with MC and experimental groups

20. Conclusions Open a link between the Geant4 Collaboration and the experimental groups working in underground physics ( & ILIAS) Geant4 Collaboration willing toaddress the requests(expecially for validation) coming from our community A lot of work! Requires constant feedback and support from the experimental groups Validation & cross-check should be done in synergy Present ILIAS activity of cross-check and comparison between different Monte Carlo codes is very welcome

21. The validation of Geant4