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ppt - Geant4 - Cern

VIEWS: 1 PAGES: 30

									            GEANT4 CMS SIMULATION


                      Pedro Arce (CERN/CIEMAT)
                     (on behalf of CMS collaboration)




GEANT4 workshop 02            CMS GEANT4 Simulation   Pedro Arce (CERN/CIEMAT)   1
                         Outline

     • OSCAR functionality
     • OSCAR/GEANT4 robustness and performance
     • Physics comparisons




GEANT4 workshop 02       CMS GEANT4 Simulation   Pedro Arce (CERN/CIEMAT)   2
                     OSCAR functionality: Geometry
   • All CMS detectors
   • Also several Testbeams

   • Currently moving to geometry in XML database, common to
   Simulation/Reconstruction/Visualisation
        • All geometry converted from GEANT3 geometry
        • Building of XML geometry into GEANT4 ready
        • Already can be visualised with IGUANA (heavily used for debugging)
        • Missing: detector numbering schemes with new geometry
        • Will need to review the use of ‘SetSmartLess’ (3 years old)
   • Detailed checking quite advanced
        • Thorough comparison of GEANT3 and GEANT4 geometry
             • All materials, volumes and touchables properties
             • Positions of touchable centres
             • Material budget
        • CMS Overlap Detection Tool (now in GEANT4)
GEANT4 workshop 02                        CMS GEANT4 Simulation   Pedro Arce (CERN/CIEMAT)   3
                          Geometry for OSCAR

 XML based Detector
 Description Language
 (XML DDL)
 - Single description inter-
   face for the ideal detector
 - Generic description
   . Materials
   . Geometry
   . Component approach
 - Attaching specific
   Information to
   . Components
   . Subsets of Volumes
 - Human editable/readable
   /expandable


GEANT4 workshop 02               CMS GEANT4 Simulation   Pedro Arce (CERN/CIEMAT)   4
                Sliced view of CMS barrel detectors


  View of CMS muon system




          View of 180 Higgs event simulated in
                 CMS Tracker detector

GEANT4 workshop 02                  CMS GEANT4 Simulation   Pedro Arce (CERN/CIEMAT)   5
            OSCAR functionality: Primary generator
  • CMS particle gun:
       • Scan in , , energy
       • Random (flat/gaussian) in , , energy
  • Interface with HEPEVT ASCII files
  • Interface with PYTHIA ntuples
  • Long-life particles:
       • In GEANT3 only the decay products are simulated
       • In GEANT4 the particle is simulated before decaying (and the decay products
       are kept)
            • Advantage: you take into account the possibility of interactions, energy
            loss, magnetic field bending, etc. before decaying
            • The life time is not kept
            • The momentum of decay products is not kept
       • OSCAR: user can select to simulate the particles before decaying or simulate
       decay products (keeping the life time)
           • Need deeper study to understand what will be the final solution
GEANT4 workshop 02                   CMS GEANT4 Simulation     Pedro Arce (CERN/CIEMAT)   6
                     OSCAR functionality: Persistency
      • Hits for all detectors
      • Primary generator particles
      • Selected tracks
      • Use CMS framework (COBRA)
           • Fully compatible with Reconstruction

      • Using Objectivity, moving to ROOT (end 2002)




GEANT4 workshop 02                 CMS GEANT4 Simulation   Pedro Arce (CERN/CIEMAT)   7
             OSCAR functionality: Visualisation
     Interactive visualisation is done with                 IGUANA
    • Visualise any GEANT4 Geometry
         • Select by logical volumes / by physical volumes
         • Picking, slices
         • Volume property window
    • GEANT4 command line
    • A wizard to guide through OSCAR settings
    • Adding other extensions is trivial (e.g. GUIs like overlap detection)
    • Visualise Tracks
    • Visualise magnetic field
    • Integrated with overlap detection
         • Find overlaps, show result details in a list
         • Highlight overlaps in 3D
    • Hits, in the near future
GEANT4 workshop 02                   CMS GEANT4 Simulation      Pedro Arce (CERN/CIEMAT)   8
                               OSCAR - IGUANA

                                                                             Overlap detection




    Example extension (a trivial wizard)
   Queried from plug-in database, loaded on
request and bound to IGUANA G4 Run Manager


                                                                            Control of arbitrary
                                                                              GEANT4 tree



                                                       Correlated
                                                        Picking

          IGUANA viewer displaying
             OpenInventor scene

GEANT4 workshop 02                     CMS GEANT4 Simulation        Pedro Arce (CERN/CIEMAT)       9
                     OSCAR - IGUANA: magnetic field
      • 2D plane that can be rotated
      • Field direction as an arrow
      • Field intensity as colour




GEANT4 workshop 02               CMS GEANT4 Simulation   Pedro Arce (CERN/CIEMAT)   10
                         OSCAR functionality
     Physics:
     • Electromagnetic processes needed at LHC
     • Hadronic processes needed at LHC
         CMS Physics Technical Design Report is planned to be
                written using OSCAR (due end 2005)
                     OSCAR milestone Spring/Summer 2003:
        “Reproduce the physics results of the GEANT3 simulation with
                            similar performance”

     Physics Cuts:
           • Production cuts per material
           • Minimum kinetic energy cuts per material
                • Still under investigation if we really need them
           • Time of flight cut
GEANT4 workshop 02                      CMS GEANT4 Simulation        Pedro Arce (CERN/CIEMAT)   11
                        OSCAR functionality
    UserActions:
         • Several user actions of the same type loadable on demand
    Framework:
         • COBRA manages the main() and takes care of persistency
         • Now OSCAR is being reengineered to achieve full integration
         with CMS Framework (see wednesday talk by M. Stavrianakou)

    Documentation:
         • User’s Guide updated for each release
         • doxygen documentation
         • Several Tutorials on the web
              • For OSCAR developers
              • For Physics Reconstruction software developers
              • For Summer Students
GEANT4 workshop 02                     CMS GEANT4 Simulation     Pedro Arce (CERN/CIEMAT)   12
                      OSCAR functionality
     Future developments:
           • GEANT4e as GEANE replacement (error propagation for
           track fitting)
              • Under progress

           • GFLASH for fast simulation
              • RTAG/G4 discussion



     Summary:

                OSCAR is ready for physics validation studies

GEANT4 workshop 02               CMS GEANT4 Simulation   Pedro Arce (CERN/CIEMAT)   13
                     OSCAR/GEANT4 robustness
    Several problems found:
         • Particles loop between two volumes
               push them by 0.01 mm
         • Several G4Exception found:
              • solved by CMS team or/and with the help of GEANT4
              team


    >10000 pp events without crashing


    NOTE: new G4Exception found with GEANT4.4.1 (under investigation)



GEANT4 workshop 02             CMS GEANT4 Simulation   Pedro Arce (CERN/CIEMAT)   14
           GEANT4 vs GEANT3 Time Performance

   - Full events: H / tte / Z
        - Cuts in primary particles: Pt : 1 GeV, || < 2.4 (3.0)
   - Full CMS geometry
   - 3D TOSCA magnetic field
   - Production and tracking cuts as in CMSIM (GEANT3)
   - GEANT4 voxel navigation
   - GEANT4.4.0.ref02
   - Pentium III 850 Mhz


   - Checked that they are really the same events (see next)
GEANT4 workshop 02              CMS GEANT4 Simulation   Pedro Arce (CERN/CIEMAT)   15
                            G3-G4 events detailed comparison
                No Tracks   H in all CMS (10 Events)

                                               Initial track energy




                                                                                               MeV
    No Tracks




                                               Track length




                                                                                                mm
GEANT4 workshop 02                               CMS GEANT4 Simulation   Pedro Arce (CERN/CIEMAT)    16
               G3-G4 events: detailed comparison
                Origin of secondary tracks: R vs Z
     R (mm)




                                                                   CMSIM
                                                                   (442828 tracks)




                                                        Z (mm)
      R (mm)




                                                                   OSCAR
                                                                   (427136 tracks)




                                                        Z (mm)
GEANT4 workshop 02              CMS GEANT4 Simulation            Pedro Arce (CERN/CIEMAT)   17
                     Time performance
      - H (10 events)
      CMSIM: 439k tracks              64 sec/evt
      OSCAR: 400k tracks             117 sec/evt (1.83)

      - tte (10 events)
      CMSIM: 1809k tracks            184 sec/evt
      OSCAR: 1159k tracks            425 sec/evt (2.31)

      - Z (10 events)
      CMSIM: 1105k tracks             96 sec/evt
      OSCAR: 941k tracks             248 sec/evt (2.58)

GEANT4 workshop 02       CMS GEANT4 Simulation   Pedro Arce (CERN/CIEMAT)   18
               CMSIM(GEANT3) - OSCAR(GEANT4) comparison
                             Central Tracker
       •Number of rechits per track vs eta



                           Cmsim 122

                           OSCAR 1 3 2 pre 03


     100 GeV Pt muons in region ||<2.5                 RecHits




                                                            •resolution vs eta



GEANT4 workshop 02             CMS GEANT4 Simulation   Pedro Arce (CERN/CIEMAT)   19
               CMSIM(GEANT3) - OSCAR(GEANT4) comparison:
                                  Muon System
                     reconstructed – generator quantities




                     5-200 GeV Pt muons in region ||<2.4

GEANT4 workshop 02                CMS GEANT4 Simulation   Pedro Arce (CERN/CIEMAT)   20
              Importance of tuning tracking precision parameters

• Big difference between reconstructed and generated track
parameters was found because tracking precision parameters were
too high.
• ‘deltaIntersectionAccuracy’
 is by default 100 m
     • CMS tracker precision 20 m
     • CMS Muon prcision 200 m
     • Has to be set to 0.1 m
     • Time just increased by 3%




GEANT4 workshop 02                 CMS GEANT4 Simulation   Pedro Arce (CERN/CIEMAT)   21
               CMSIM(GEANT3) - OSCAR(GEANT4) comparison:
                            EM calorimeter
• SETUP:
   • CMS electromagnetic calorimeter: lead tungstate crystals
   pointing to interaction point
   • Photon of E = 30 GeV enters front face of crystal
   • No magnetic field

• What was compared:
   • E in hottest crystal, in 3x3, in 5x5 matrix
   • E total
   • dNhits/dt, for 1 ns time slices

• GEANT3.21 vs GEANT4.4.0.p02
GEANT4 workshop 02           CMS GEANT4 Simulation   Pedro Arce (CERN/CIEMAT)   22
               CMSIM(GEANT3) - OSCAR(GEANT4) comparison:
                                       EM calorimeter
    Shower containment:                                         From GEANT4 gallery:
                                                                Electron 5 Gev in PbWO4




• GEANT3 looks wider than GEANT4
• From old test beam GEANT3/GEANT4 comparison
     CMS Note 1997/037 by A.Givernaud: good agreement with G3 for shower profile
     CMS Note 1998/031 by K.Lassila-Perini: G3 shower is a bit wider than real shower    (more detailed)
GEANT4 workshop 02                      CMS GEANT4 Simulation          Pedro Arce (CERN/CIEMAT)     23
               CMSIM(GEANT3) - OSCAR(GEANT4) comparison:
                            EM calorimeter
    Hit timing:
  • GEANT4 shower has ~8% less
  hits than GEANT3 shower

  It doesn´t contradict with
  GEANT4 gallery plot below,
  however direct comparison is
  needed:




GEANT4 workshop 02           CMS GEANT4 Simulation   Pedro Arce (CERN/CIEMAT)   24
                     ECAL + HCAL testbeam:
              GEANT3 - GEANT4 comparison
  1996 Testbeam Setup for CMS HCAL
  • A test module of copper absorber plates with scintillator tile
  sampling
      • 28 scintillator plates with absorber of varying thickness in between
  • A prototype lead tungstate crystal electromagnetic calorimeter
  • Energies: 225 GeV  (for calibration), 10-300 GeV , 10-300 GeV e-
  • Magnetic Field: 0, 0.75, 1.5, 3 tesla (direction parallel to the face of
  the scintillator)
  • Configuration: Only HCAL or ECAL + HCAL
  • 5000 events were taken for each setup
  • Response of the Calorimeter was studied as a function of:
       • Magnetic field: effect on scintillator
       • Absorber thickness: optimisation of resolution versus containment
       • Absorber depth: energy containment
       • Electromagnetic Calorimeter contribution: e/ effects
GEANT4 workshop 02                CMS GEANT4 Simulation   Pedro Arce (CERN/CIEMAT)   25
                     ECAL + HCAL testbeam:
                     GEANT3 - GEANT4 comparison
       GEANT4 4.0.p02
                       100 GeV pi+     0 Tesla          ECAL+HCAL




GEANT4 workshop 02              CMS GEANT4 Simulation        Pedro Arce (CERN/CIEMAT)   26
                     ECAL + HCAL testbeam:
                     GEANT3 - GEANT4 comparison

                       100 GeV e-   0 Tesla       HCAL




GEANT4 workshop 02              CMS GEANT4 Simulation    Pedro Arce (CERN/CIEMAT)   27
                     ECAL + HCAL testbeam:
                     GEANT3 - GEANT4 comparison
                           pi+   0 Tesla         ECAL+HCAL
           Events with MIP in ECAL                       Events with shower in ECAL




GEANT4 workshop 02                   CMS GEANT4 Simulation       Pedro Arce (CERN/CIEMAT)   28
                     ECAL + HCAL testbeam:
                     GEANT3 - GEANT4 comparison
                            pi+   0 Tesla         ECAL+HCAL
            Events with MIP in ECAL                       Events with shower in ECAL




GEANT4 workshop 02                    CMS GEANT4 Simulation       Pedro Arce (CERN/CIEMAT)   29
                              Summary
  • OSCAR is technically complete to start with physics studies
  • Some comparisons vs CMS GEANT3 simulation started
       – Some problems found, but solved by CMS + GEANT4
  • Some TestBeam comparisons started:
       – Show reasonable agreement with data
       – Slightly better than GEANT3
       – Others to be done: ECAL TB ‘99, ECAL TB ‘02, ECAL+HCALTB ‘99,
         HCAL ‘02, Tracker ´02
  • Next months: systematic comparison with GEANT3 simulation
       – Plan to move to GEANT4 simulation by Summer 2003




GEANT4 workshop 02              CMS GEANT4 Simulation   Pedro Arce (CERN/CIEMAT)   30

								
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