Geant4 “Standard” Electromagnetic Physics Package

1. Geant4 “Standard” Electromagnetic Physics Package Geant4 Standard EM group MC 2005 Chattanooga, Tennessee, USA 17-21 April 2005

2. Geant4 Standard EM group H.Burkhardt, V.M.Grichine, P.Gumplinger, V.N.Ivanchenko, R.P.Kokoulin, M.Maire, L.Urban BINP, Novosibirsk, Russia CERN, Geneva, Switzerland ESA, Noordwijk, The Netherlands LAPP, Annecy, France LPI, Moscow, Russia MEPhI, Moscow, Russia RMKI, Budapest, Hungary TRIUMF, Vancouver, Canada G4 Standard EM

3. Outline • Standard EM package • Overview on major developments since 2003 • Validation/comparisons • EM PhysicsLists • Acceptance suite • New developments • Conclusions G4 Standard EM

4. Standard EM package • Naturally continue Geant3 EM physics • Include a complete set of models for simulation of electromagnetic processes in the energy range from 1 keV to 10 PeV • Includes optical photons production and transport • Focus on HEP experiments, well applicable for instrumentation, space, and medicine studies G4 Standard EM

5. Design iteration in Standard EM package • Standard EM package was one of physics package working from 1st Geant4 release • Created using Geant3 expertise • Used practically in all Geant4 applications • LHC experiments • Space and medicine applications • Used in production for BaBar for many years • Some architecture problems were accumulated • In 2003 the package were redesigned • New developments were enabled G4 Standard EM

6. Major activities since 2003 • Physics improvements: • Evolutions of multiple scattering model • Hadron ionization was updated • New ion ionization • Muon processes were updated • Updated cross section for Compton effect • Revised PAI models • New high energy processes • Evolution in optical photons simulation • Cut per region from G4 5.1 • Model design from G4 6.0 G4 Standard EM

7. Hadron/ion ionization (1) • Corrected Bethe-Bloch formula for the Ekin>2 MeV • ICRU49 parameterization is used for the Ekin< 2 MeV • Scaling relation for other hadrons/ions • Ion effective charge is recalculated at each step of the particle and is used also for tracking in EM field G4 Standard EM

8. Hadron/ion ionization (2) • Review of corrections to the Bethe-Bloch formula • C – shell correction (was asymptotic formula) • G – Mott correction (new) • δ – density correction • F – finite size correction (new) • L1- Barkas correction (new) • L2- Bloch correction (new) • New class G4EmCorrections G4 Standard EM

9. Integral approach • EM cross sections depend on energy • Precision of interaction probability depends on step size and energy change • Integral approach: interaction probability is sampled using integral method (MC’91 Proceedings) • Integral approach allows to have any step size for ionization constant integral G4 Standard EM

10. Performance comparison 5.2/6.2 Intel 2.4GHz 512 KB • Performance improved after design iteration • Initialization time smaller by 2 times for complecate geometry and much more for simple geometry • Size of EM tables smaller by 2 times or more (HARP, CMS) • CPU per event less at least by 10% • Higher performance for low cuts G4 Standard EM

11. Geant4/Penelope comparison(End point of secondaries e-) 1.25 MeV gamma in 1 mm Si G4 Standard EM

12. HEP Calorimetry Average energy deposition in lAr • G4 5.2p02 close to G3 • G4 6.2p02 include integral method • G4 7.0 include msc modification • Integral method for tracking and updated model of multiple scattering provide less cut dependent results G4 Standard EM

13. Geant4 muon interactions • Basic processes: • Ionisation • Bremsstrahlung • Production of e+e- • Muon-nuclear interactions • Muon production and transport in Geant4 is available up to 10 PeV Muon differential cross sections G4 Standard EM

14. Verification theory/Geant4difference less than 5% G4 Standard EM

15. New High energy EM processes • EM background due to high energy EM interaction with media: •  → µ+µ- (~Z2) • e+ µ+µ- (~Z) • e+ +- (~Z) • Visible at LEP and High at SLC • Of concern for linear colliders G4 Standard EM

16. Background for linear collider Angles of muons 250 GeV beam High energy e+, e-, and  can produce µ+µ- pair 1010 e / bunch After collimator ~ 103 µ+µ- G4 Standard EM

17. User support • Physics Reference Manual : complete description of models/sampling methods • Extended examples : PhysicsLists, user actions, visualization, analysis tools • Standard group support • 12 extended/electromagnetic examples • 1 extended/medical example • 1 extended/optical examples • 3 novices • Hyper News discussions G4 Standard EM

18. To insure stability of results with time To control performance Is based on extended electromagnetic examples G4EmCalculator is an interface to dE/dx and cross sections Control on summary numbers: Average energy deposition Shower shape Scattering angles Tests on cross sections and dE/dx Comparison of histograms (in project) Acceptance suite for Standard EM package G4 Standard EM

19. New developments and plans for Standard EM package • Predefined G4Elements and G4Materials with parameters from the NIST data base will be available in the release 7.1 • Gamma processes in model design • Comparisons/validation • Long-term prospects: • Physics model on level of theory/experiment for all processes • High energy extensions • Further performance improvement • Complete automatic acceptance suite G4 Standard EM

20. Conclusions • Geant4 Standard EM package is used in production of Monte Carlo results for many years • Recently the package has been redesigned • Physics was extended and improved • Performance was improved • There are plans to extend energy range of the Standard physics G4 Standard EM