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Geant4 toolkit for simulation of HEP experiments
V.Ivanchenko From name of Geant4 collaboration BINP, Novosibirsk, Russia & CERN, Geneve, Switzerland


Outline
Geant4 history Design and tools Geant4 physics June 2002 release Prospects for future

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History
90th: About 100 FORTRAN MC programs in the world. The most popular in HEP GEANT3. R&D project start in 1994 to develop a detector simulation toolkit for HEP Software Engineering, OO technology, and c++ World-wide collaboration Requirements from:
­ LHC ­ heavy ions, CP violation, cosmic rays, medical and

space science applications

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History
1995 ­ prototype 1997 ­ alpha-version (main functionality) Dec '98 - Geant4 0.0 release Geant4 collaboration was created ... Dec '01 ­ Geant4 4.0 release June '02 ­ Geant4 4.1 release
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Working Groups
For G4 subdomains
­ Run, Events & Detector ­ ­ ­ ­ ­ ­ ­ User and Category

Response Tracking Geometry & Transportation, Generic Processes & Materials Hadronic Physics, E.M. Physics ("Standard"), Low Energy EM Physics (since 2000)

Interfaces ­ Visualization

For software:
­ Software Management ­ Testing & QA ­ Documentation

Management

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Class Category Diagram
RUN RUN UI_GUI UI_GUI DIGI DIGI HIT HIT
CAD IO CAD IO FIELDS FIELDS
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Persistency Visualization Persistency Visualization

EVENT .. EVENT

GENERATOR GENERATOR

AIDA AIDA

TRACKING TRACKING PHYSICS PHYSICS GEOM GEOM
TRACK TRACK MATERIAL MATERIAL
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PARTICLE PARTICLE

Intercoms, global Intercoms, global

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Geant4 physics
Main goal of G4 is good physics To achieve the goal OO approach is fundamental Independent, alternative physics models Existing components are integrated and new model continue to be developed
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BABAR SVT

G4 processes
Physics is described via abstract interface called

process associated with particles

Distinction between process and model ­ one process may includes many models Generation of final state is independent from the access and use of cross sections and from tracking Transparent access to cross sections and secondary generators Use of public evaluated databases
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Standard interface: a process provides Interaction Lenths, StepLimits, and DoIt methods Processes active AlongStep, PostStep, AtRest There are following processes:
Electromagnetic Hadronic Decay Optical Transportation Parameterized
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G4 processes

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Electromagnetic physics
Subcategories:
Muons Lowenergy Standard Xrays

Main processes:
Ionisation Bremssrahlung Multiple Scattering Gamma Convertion Compton Scattering Photoelectric effect Synhrotron radiation Transition radiation Cherenkov radiation Rayleigh effect

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No tracking cuts, only production thresholds Default G4 ­ thresholds for production secondaries are expressed in range, universal for all media,
Range 10 keV gamma in Si 2 cm Range of 10 keV electron in Si 2 microns

Geant4 cuts

Energy thresholds for a material is calculated from this cut in range. In 2002 a possibility to set a cut by logical volume will be implemented
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G3/G4 cuts in Pb/Ar calorimeter
Protons 500 MeV

G3
Cut 450 keV Ar Pb Ar

G4
1.5 mm - 450 keV LAr 2 MeV Pb
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G4 electromagnetic physics
LPM effect for Bremsstrahlung Electron backscattering

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Low energy EM physics

Low energy EM physics required using detailed information about atomic shells Instrumentation studies, space, and medical applications Cross sections and energy spectrums are taken from EEDL, EADL, EPDL, ICRU, and others databases The state of media (solid, liquid, gas) and chemical structure is taken into account
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Geant4 space applications
Cosmic rays, jovian electrons

X-Ray Surveys of Solar System Bodies
Solar X-rays, e, p

Geant3.21 ITS3.0, EGS4
Courtesy SOHO EIT

Geant4 C, N, O line emissions included

Induced X-ray line emission: indicator of target composition (~100 µm surface layer)
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G3/G4/Data comparison

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Model approach ­ cross sections and secondary generation are separated. Based of evaluated data libraries: ENDF, Jef, EFF, JENDL, FENDL, CENDL, ENSDF, Brond, and MENDL. Following models are exist now:
Elastic Cascade Chiral_inv_phase_space Pre-equilibrium High_energy parameterized Low_energy parameterized Isotope_production Neutron_hp Stopping Radiative_decay June,24 ACAT-2002 V.Ivanchenko Geant4

G4 hadronic processes

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G4 hadronic processes
The set of models provides simulation of neutron transport, elastic and inelastic nuclear interactions of photons, leptons, and hadrons Results of comparison project, for example ATLAS pion testbeam (A.Kiryunin, Calor'2002), demonstrates reasonable agreement with G4 predictions All details about G4 hadronic in talks of J.P.Wellisch and M.Kosov
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Status of G4 HEP applications
In 2001 BABAR dropped G3 and is using G4 for production, >3·108 events are generated GLAST accept G4 ATLAS ­ geometry, transition radiation, accordion type calorimeter, comparison projects
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ATLAS

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Status of G4 HEP applications
CMS ­ geometry is ready, production is planed for 2002 ALICE ­ comparisons of hadronic physics LHCb ­ Gaudi framework, geometry, Airogel detailed model TESLA - R&D / detector optimization
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Status of G4 HEP applications
HARP (CERN) is based on G4, TPC detailed study, validation of hadronic models, T9 beam line simulation BTeV ­ testbeam FNAL ­ R&D on muon beam transport and muon culling ... others
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HARP

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Geant4 in Novosibirsk
Optimization of detectors for medicine SND at VEPP-2000 required transition UNIMOD2 G4 R&D on detailed model of tracker Comparison of G4 and SND data for , K
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User support
Two public releases per year Intermediate releases available for G4 members and for beta-testers About 30 integration tests and about 20 examples Regression suit in progress HyperNews system (SLAC) Automatic bug report system Documentation review
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June'2002 release
GDML: consolidate implementation of XML browser Parameterized 3D voxelisation Consolidation of solid/volume reflections Gamma into muon pair convertion Updated multiple scattering Ionisation for fragments Auger effect MARS-13 re-write ­ leading particle biased code for energies below 5 GeV Include heavy fragments to evaporation Update of gamma ­ nuclear and electro-nuclear cross sections/ models
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Future perspectives
Cut per region ­ key design iteration for LHC Design iteration in EM processes New electromagnetic processes for TeV energies Improvement of low energy EM models Continued improvement of hadronic models Providing `educated guess' physics lists for major use-cases (like LHC detector simulation) Validation of G4 physics ­ first priority Close collaboration with HEP experiments
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