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Geant4 status and applications. John Apostolakis, CERN for Geant4 collaboration. Contents. Geant4’s kernel EM Physics processes Comparisons with data Hadronic framework, models Utilization of Geant4 Status and plans Geant4 4.0 to be released Friday 14 th. G EANT 4.

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Geant4 status and applications


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    1. Geant4 status and applications John Apostolakis, CERN for Geant4 collaboration

    2. Contents • Geant4’s kernel • EM Physics processes • Comparisons with data • Hadronic framework, models • Utilization of Geant4 • Status and plans • Geant4 4.0 to be released Friday 14th

    3. GEANT 4 • Detector simulation tool-kit for HEP • offers alternatives, allows for tailoring • Software Engineering and OO technology • provide the method for building, maintaining it. • Requirements from: • LHC • heavy ions, CP violation, cosmic rays • medical and space science applications • World-wide collaboration

    4. Geant4 Collaboration Collaborators also from non-member institutions, including Budker Inst. of Physics IHEP Protvino MEPHI Moscow Pittsburg University

    5. Geant4 Capabilities • Powerful structure and kernel • tracking, stacks, geometry, hits, … • Extensive & transparent physics models • electromagnetic, hadronic, … • Framework for fast simulation • Additional capabilities/interfaces • persistency, visualization, ...

    6. Creates & manages runs, events, tracks a run is configuration of geometry, physics & event generator. Allows particles to be prioritized easily at no cost 3 default stacks, postponement. Tracking is general (unique) physics lists can be tailored for different use cases Enables the creation of user-defined hits able to handle pile-up. Versatile volumes and navigator for Geometry Geant4 kernel

    7. Describes a Detector Hierarchy of volumes Many volumes repeat Volume & sub-tree Up to millions of volumes for LHC era Import detectors from CAD systems Navigates in Detector Locates a point Computes a step Linear intersection Field propagation Geant4 geometry: what it does

    8. Propagating in a field Charged particles follow paths that approximate their curved trajectories in an electromagnetic field. • It is possible to tailor • the accuracy of the splitting of the curve into linear segments, • the accuracy of each intersection of a volume boundary, trading accuracy against performance. • These can be set to different values for a single volume or for a hierarchy.

    9. Electromagnetic processes Initial goal (RD44) was to create EM physics at least at equivalent to Geant-3 New concepts were pursued: • Distinction between production threshold and tracking cut • Expressing production cuts in terms of range instead of energy • Creating an effective range from the distance to the nearest boundary

    10. Electromagnetic processes Processes new to Geant4 • Multiple Scattering: new model • includes lateral displacement • no path length restriction • New process: Transition radiation • from physics models • Photo-Absorption Ionisation model • Alternative energy loss Referred to as PAI model

    11. Electromagnetic physics • Gammas: • Gamma-conversion, Compton scattering, Photo-electric effect • Leptons(e, m), charged hadrons, ions • Energy loss (Ionisation, Bremstrahlung) or PAI model energy loss, Multiple scattering, Transition radiation, Synchrotron radiation, • Photons: • Cerenkov, Rayleigh, Reflection, Refraction, Absorption, Scintillation • High energy muons and lepton-hadron interactions • Alternative implementation (“low energy”) • for applications that need to go below 1 KeV • Down to 250eV (e+/g), O(0.1) mm for hadrons

    12. Shower profile 1 GeV electron in H2O G4, Data G3 • Good agreement seen with the data

    13. Cuts, in kernel & user hook • No tracking cut • particles are tracked down to zero energy, range • Coherent “production cuts” for secondaries • validity range of models fully exploited • kernel can enforce consistent production cuts • yet processes can ask to override when they need to. • treatment of boundary effects (Figures) • Cuts in range rather than Energy • Geant3 used cuts in Energy - inefficient • significant gain in results quality vs CPU usage • User can cut inEnergy, track length, TOF ..

    14. GEANT4 Cut: 2mm Pb 2.5 MeV CO255keV 5cm Pb, CO2, Pb, CO2 GEANT3

    15. Changing cuts • Results much more stable in variation of cuts • even track length • Also see shower profiles for different cuts (next slide) • between 10mm and 50 microns

    16. PbWO4 5 GeV e-

    17. Lead CO2 Lead CO2 Secondaries produced only if they could escape Range < safety Secondaries CANNOT leave Pb: NOT produced Range > safety Secondaries could leave Pb: produced

    18. Sampling calorimeter • Sampling calorimeter • visible energy • tests • all EM processes for e-, e+ and photon • Data from Sicapo Col. NIM A332 (85-90) 1993

    19. Alternatives for Energy Loss • ‘Standard’ differential • Extended down to 1 KeV • Creates more secondaries near volume borders • Photo-absoption Ionisation model • increased precision • suited for gases/thin absorbers • Utilised in ATLAS TRT detector • ‘Low-energy’ down to 250 eV • with shell effects, … • Integral Energy Loss processes • Current implementation withdrawn for now (maintenance/uses)

    20. Multiple scattering model • A new model for multiple scattering based on the Lewis theory is implemented • since public b release in 1998. • It randomizes momentum direction and displacement of a track. • Step length, time of flight, and energy loss along the step are affected, and • It does not constrain the step length.

    21. Multiple scattering • Examples of comparisons: • 15.7 MeV e- on gold foil (figure this page) Thanks to L. Urban Angle (deg)

    22. Multiple Scattering: One new development Thanks to L.Urban Included in Geant4 4.0

    23. Low energy EM processes • Photons, electrons down to 250 eV • Xsec from EADL libr. • Thanks to M.G. Pia, P. Nieminen, .. • Hadron EM interactions • See 5-001 for an overview of Geant4 Low Energy EM Physics E(KeV) Photon transmission through 1 mm Pb, showing shell effects

    24. Comparison projects • Established join projects for comparing Geant4 with experiment or test-beam data. • Results of EM comparisons: 2000-2001. • Collaboration with experiments • ATLAS (projects with data of test beams of 4 calorimeters) • BaBar (with experiment data for tracker, drift chamber) • Following slides are taken from the presentations of the experiments at conferences & workshops • For latest example: see presentation of D. Barberis at LC workshop, CERN 15 Nov 2001.

    25. Thanks to R. Manzini, P. Loch, Atlas FCAL

    26. Atlas FCal1 electron Energy resolution Thanks to Rachid Manzini & Peter Loch & Atlas FCAL

    27. A 50 GeV e- in the Atlas EM barrel calorimeter

    28. Liquid Argon EM Calorimetry muons in LAr EM Barrel Thanks to G. Parrour, K. Kordas Atlas LAr

    29. Liquid Argon EM Calorimetry electrons in LAr EM Barrel Linearity of response: - within 0.5% Thanks to Gaston Parrour, Kostas Kordas, Atlas LAr

    30. Liquid Argon EM Calorimetry • Geant4 describes better than Geant3 energy deposits as measured with muon test beam data – agreement G4-test beam is within 1% • Geant4 (as well as Geant3) describes well the linearity of electron response • Geant4 predicts larger energy resolution for electrons that Geant3. Direct comparison with test beam data still in progress

    31. Liq Argon Hadronic Calorimetry pion shower in LArHadronic End Cap electron energy resolution in LAr Hadronic End Cap

    32. Liquid Argon Hadronic Calorimetry • Electrons: • Geant4 predicts less visible energy in LAr than Geant3 (~3%) and more energy in absorber (~0.1%). Total energy is the same • energy resolution well reproduced by Geant3: Geant4 gives too good resolution • Pions: • first results of simulation with Geant4 look reasonable • more detailed comparisons with test beam data in progress • open questions being discussed with Geant4 people pion energy resolution inLAr Hadronic End Cap

    33. Tile Calorimeter: electrons =0.35 in Tilecal module 0 • Electron energy resolution somewhat too good: sampling term 16% instead of 24% (was the same for Geant-3) • Visible energy vs impact point has the correct shape but amplitude of variations and energy dependence do not match test beam data Electron energy resolution Visible energy vs impact position for 20 GeV and 100 GeV electrons

    34. Observations on thecomparisons • Geant4 results are more stable than Geant3 • Many results of Geant4 versus data • reasonable agreement seen in many observables, • issues/differences exist that need to be resolved. • Invaluable feedback obtained, with improvements developed and planned. • The good spirit of the collaboration has allowed us to resolve many issues (THANKS).

    35. Hadronic processes • Five level implementation framework • allows models to be used in combination at different levels • Solving the mix and match problem in the framework • Variety of models and cross-sections • for each energy regime, particle type, material • alternatives with different strengths and computing resource requirements • Components can be assembled in an optimized way for each use case. • A simple example is illustrated in figure (next page)

    36. Assembling processes Element • Illustrative example of assembling models into an inelastic process for set of particles • Uses levels 1 & 2 of framework particle Pre-compound model Energy CHIPS QGSM Parame- terized

    37. Hadronic processes • Each hadronic process may have one or more • cross section data sets and • final state production models associated with it. Each one has its own applicability. • We define “data set” and “model” broadly • A “data set” is an object that encapsulates methods and data for calculating total cross sections. • A “model” is an object that encapsulates methods and data for calculating final states.

    38. Hadronic processes at rest • At Rest processes • pion absorption • kaon absorption • neutron capture • antiproton annihilation • antineutron annihilation • mu capture • At Rest processes may generate secondaries after some time interval.

    39. Hadronic processes in flight • Four types of processes • Elastic scattering • Inelastic scattering • Fission • Capture • Examples • Parameterization driven models originally based on GHEISHA with many improvements • Data driven models based on ENDF/B-VI • Theory driven models for inelastic scattering

    40. Modeling approaches 1. Data driven approach • Neutrons • from numerous evaluated data libraries • down to thermal energies, up to 20 MeV • Isotope production (see next slide) • Induced Fission & Capture (H.Fesefeldt) • used above 20 MeV • Photon-evaporation, radioactive decay, etc. 2. Parameterized models • Gheisha + fixes + new parameterizations (H.F, TRIUMF)

    41. Modeling approaches (cont.) 3. Theoretical models, from low E to high E • Pre-Compound Model + Evaporation Phase • Cascades, CHIPS and QMD models • String models • Excitation, fragmentation, hadronisation models • Interface to event generator(s) • In future

    42. Pre-Compound Model & Evaporation Phase • Traditional pre-equilibrium model • as good as existing ones • Evaporation: • Weisskopf-Ewing model • Fermi breakup model • Model for fission • Multi-fragmentation model (Bondorf) • Photon Evaporation • only missing Internal Conversion • (suppressed by more than 10^4, funding expected) • Future: 2nd Pre-Compound, from HETC re-eng. (in 2002)

    43. Cascade energy range • Parameterized • Chiral Invariant Phase Space decay,“CHIPS” • 1st implementation now (Jefferson Lab.) • collaboration milestone 2001 (in release) • Bertini cascade (from HETC) • collaboration milestone for 2001(missed) • Kinetic model (INFN, Frankfurt): future • Further future: Relativistic QMD (Frankfurt), rewrite of INUCL code (Helsinki)

    44. String models • FTF string model, derived from Fritiof • but no Rutherford scattering • Quark Gluon String model (~ Dual Parton) • for proton, neutron, p, K+/K- induced reaction • string decay as in JETSET • following Kaidalov’s formulation • using FTF algorithm for energy transfer in case of single diffraction (~6% cases) future: K0, g, anti-nucleon induced reactions

    45. Future additions • Quark molecular dynamics model (Frankfurt) • Nucleus-Nucleus • via QMD (Frankfurt) • for light nuclei using pre-compound and cascades • ablation/abration model • Parton cascade (ansatz of K. Geiger) • ‘Re-use’ of Pythia7 • for hadron-nuclear & hadron-hadron interactions

    46. Some of the Improved Hadronic Physics 1999-2001 • Neutron & proton induced isotope production models • up to 100 MeV (J.P. Wellisch) • Multi-fragmentation and pre-compound • redesign & refinement (V. Lara) • Additional string model (J.P.Wellisch) • for proton, neutron, p, K+/K- induced reactions • Special cross-section classes for neutron, proton, and ion induced reactions (D. Axen, M. Laidlaw, J.P.W.) • Retuning of High Energy Models (H. Fesefeldt) | (JPW) • Doppler broadening of neutron X-section on the fly

    47. Isotope Production • Isotopes produced by neutrons on Lead 208 • Small dots: evaluated data • Circles with error bars: Geant4 • latest model • included since Geant4 1.0 J.P.Wellisch

    48. CHIPS • New physics model/event generator • From ~100 MeV to ~10 GeV • Applications to date: • Pbar annihilation at rest • Pi capture • Gamma-nucleus interactions • Intranuclear transport • after high energy interaction • Schedule for release end 2001

    49. Pion capture on 12 C nucleus