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Geant4 “Standard” Electromagnetic Physics Package Geant4 Standard EM group MC 2005 Chattanooga, Tennessee, USA April 2005

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M. Maire, MC'2005G4 Standard EM2 Geant4 Standard EM group H.Burkhardt, V.M.Grichine, P.Gumplinger, V.N.Ivanchenko, R.P.Kokoulin, M.Maire, L.Urban 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

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M. Maire, MC'2005G4 Standard EM3 Outline ► Standard EM package ► Overview on major developments since 2003 ► Validation/comparisons ► EM PhysicsLists ► Acceptance suite ► New developments ► Conclusions

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M. Maire, MC'2005G4 Standard EM4 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

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M. Maire, MC'2005G4 Standard EM5 Design iteration in Standard EM package ► Standard EM package was one of physics package working from 1 st 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

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M. Maire, MC'2005G4 Standard EM6 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

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M. Maire, MC'2005G4 Standard EM7 Hadron/ion ionization (1) ► Corrected Bethe-Bloch formula for the E kin >2 MeV ► ICRU49 parameterization is used for the E kin < 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

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M. Maire, MC'2005G4 Standard EM8 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) L 1 - Barkas correction (new) L 2 - Bloch correction (new) ► New class G4EmCorrections

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M. Maire, MC'2005G4 Standard EM9 High order corrections ► Are important at high energies ► Are important for ions ► Are implemented in G4EmCorrections class for both Standard and Low-energy packages ► Finite size: ► Mott:

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M. Maire, MC'2005G4 Standard EM10 Result of refinement of stopping power – Geant4 and NIST are within systematic uncertainty of the data

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M. Maire, MC'2005G4 Standard EM11 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

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M. Maire, MC'2005G4 Standard EM12 Performance comparison 5.2/6.2 ► 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 Intel 2.4GHz 512 KB

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M. Maire, MC'2005G4 Standard EM13 PAI model evolution ► 2 models in G4 6.2: G4PAIModel G4PAIPhotonModel ► Ionization in very thin absorbers ► Based on Sandia tables of photo- absorption ► Models can be defined for G4Region (TestEm8) ► Any cut can be used ► Sampling of single clusters in gaseous detectors ► TRD detectors simulation ► Space and medical applications

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M. Maire, MC'2005G4 Standard EM14 Multiple Scattering Evolution

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M. Maire, MC'2005G4 Standard EM15 Geant4/Geant3/Data comparisons

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M. Maire, MC'2005G4 Standard EM16 Geant4/Penelope comparison (End point of secondaries e-) 1.25 MeV gamma in 1 mm Si

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M. Maire, MC'2005G4 Standard EM17 Geant4/EGSnrs comparisons (Emily Poon results G4 6.1) ► There is an agreement in general on the depth dose profile ► Results are sensitive to cuts and step limits

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M. Maire, MC'2005G4 Standard EM18 HEP Calorimetry ► 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 Average energy deposition in lAr

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M. Maire, MC'2005G4 Standard EM19 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

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M. Maire, MC'2005G4 Standard EM20 Muon energy loss ► Continuous energy loss in Geant4: ► Contribution from processes: ► Ionization ► Bremsstrahlung ► Production of e + e - ► T cut – cut energy ► Transfers above T cut are sampled ► Recent upgrade: Radiative corrections to ionization at E > 1 GeV Improve precision of double differential cross section for pair production (biases reduced from 30% to 5%) Initialization time decreased Total muon energy loss

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M. Maire, MC'2005G4 Standard EM21 Verification theory/Geant4 difference less than 5%

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M. Maire, MC'2005G4 Standard EM22 New High energy EM processes ► EM background due to high energy EM interaction with media: ► → µ + µ - ( ~Z 2 ) ► e + µ + µ - ( ~Z) ► e + + - ( ~Z) ► Visible at LEP and High at SLC ► Of concern for linear colliders

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M. Maire, MC'2005G4 Standard EM23 Background for linear collider High energy e +, e -, and can produce µ + µ - pair e / bunch After collimator ~ 10 3 µ + µ - Angles of muons 250 GeV beam

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M. Maire, MC'2005G4 Standard EM24 PhysicsList for EM use-cases ► First release G4 6.2 ► Use modular structure with different builders: QED ( , e +, e - ) Muons (µ +, µ - ) Hadrons/ions High energy Decay Limited hadron physics ► Builders for G4 6.2 and G4 5.2 ► No precompiled library ► Are tested inside EM examples ► G4EmOptions for steering Min, max energies Cuts Step limits Gamma Therapy example – different models

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M. Maire, MC'2005G4 Standard EM25 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

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M. Maire, MC'2005G4 Standard EM26 Acceptance suite for Standard EM package ► 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)

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M. Maire, MC'2005G4 Standard EM27 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

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M. Maire, MC'2005G4 Standard EM28 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

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