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BESIII Simulation Software

BESIII Simulation Software. Deng Ziyan, IHEP ACAT 2007, Amsterdam April 23-27. Outline. BESIII experiment BESIII offline software Simulation Algorithm Performance Summary. BEPCII and BESIII. BEPC (Beijing Electron-Positron Collider) BESI/BESII detector worked on it from 1988 to 2005

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BESIII Simulation Software

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  1. BESIII Simulation Software Deng Ziyan, IHEP ACAT 2007, Amsterdam April 23-27

  2. Outline • BESIII experiment • BESIII offline software • Simulation Algorithm • Performance • Summary Deng Ziyan, IHEP

  3. BEPCII and BESIII • BEPC (Beijing Electron-Positron Collider) • BESI/BESII detector worked on it from 1988 to 2005 • Beam energy: 1.5 - 2.8GeV • BEPC  BEPCII • Luminosity: • 1.0×1031cm-2s-1  1.0×1033cm-2s-1 • Number of beam bunches: • 1 93 • BESIII: a new spectrometer to be working on BEPCII • Very good energy and angle resolution for photon measurement • Accurate 4-momenta measurement of charged particles with low momentum • Good hadron identification capabilities    Deng Ziyan, IHEP

  4. BESIII Detector • MDC • Small cell, He gas based main drift chamber • TOF • Plastic scintillator based PID system • EMC • CsI(Tl) crystal electromagnetic calorimeter • SSM • Superconducting solenoid magnet of 1T • MUC • RPC based muon counter Detector moving into the collision region by Jan. 2008 Deng Ziyan, IHEP

  5. calibUtil Services Gaudi services Gaudi Client Calibrator Register, write Search Read Simulation Pre-tracking Calibration Detector-Geo Cal-MDC Cal-TOF Fast-track Event-T0 Reconstruction Gaudi Physics Analysis Exp. data MC data Post-tracking EventDisplay Cal-Data Control-Data MDC-track EMC(B/E) TOF(B/E) MUID Metadata (persistent) MySQL rdbms REC Data Phy-tracking V0FIND EVERTEX DST Made DST Data BESIII Offline Software System BOSS Calibration & Database FACS Reconstruction Simulation Generator Transient Data Store Simulation Digitization Deng Ziyan, IHEP

  6. Developed in BOSS framework Based on Geant4 toolkit External packages Geant4.8.1+p01 GCC 3.2.3 CLHEP 1.9.2.3 GDML 2.8.0 Xerces_C 2.7.0 ROOT 4.03.02 Components Geometry description Event Generator Physics processes Magnetic field Digitization MC truth Data I/O Trigger simulation Background mixing Simulation Algorithm Project Leader: Liu Huaimin Cao Guofu, Deng Ziyan, He Miao, Liang Yutie, Pan Minghua, You Zhengyun, Yuan Ye Deng Ziyan, IHEP

  7. Detector Description xy (z=0) yz (x=0) Deng Ziyan, IHEP

  8. Detector Description stereo cell: G4TwistedTub MDC TOF G4IrregBox EMC MUC Deng Ziyan, IHEP

  9. Class for Special Geometry • G4TwistedTub • Lately imported to Geant4 source code • Error in step calculation at special points inside MDC stereo cells, step out of world volume • already reported to the author • G4IrregBox • Not in current Geant4 release • Useful in many experiments, such kind of geometry is hoped to be included in later Geant4 and GDML release Deng Ziyan, IHEP

  10. Geometry, Materials, Alignment… XML writer XML description GEANT4 Schema ROOT Schema ROOT Schema Classes for Simulation Classes for Reconstruction Classes for Event Display Detector Description with GDML • GDML (Geometry Description Markup Language), originally developed by Geant4 group • Peking University group expanded the GEANT4 Schema and developed a new ROOT Schema for BESIII applications. • GDML Detector Description can be used for simulation, track extrapolation, event display and reconstruction. Deng Ziyan, IHEP

  11. Event Generator • BES has ~30 event generators written in Fortran • Use C++ HepEvt_Wrapper to access the kinematics infor generated by the generators • Other generators • EvtGen, Bhlumi, KKMC • G4HepMCInterface being used • Why removed in latest Geant4 release? Deng Ziyan, IHEP

  12. Physics Processes General: decay, transportation Electromagnetic: standard (used), low energy (tried), optical photon (not used) Hadronic: hadron in flight: elastic, inelastic hadron at rest: absorption, capture Different hadronic models used and compared: LHEP: LEP/HEP parameterized model QGSP: Quark-Gluon String Precompound, theory driven model Deng Ziyan, IHEP

  13. Physics Processes • Bugs in hadronic processes • Classes list (Geant4.8.1+p01) • G4LEAntiProtonInelastic • G4HadronElastic • G4UHadronElasticProcess • G4MuonMinusCaptureAtRest • G4NucleiProperties • G4InelasticInteraction • Cause dead-loop or crash, hard to detect • Modification or protection made in our Geant4 package • Reported to Geant4 team, also confirmed by other groups and users Deng Ziyan, IHEP

  14. Hadronic Models (QGSP) Old: Geant4.7.1 New: Geant4.8.1+p01 Energy(GeV) Energy(GeV) no obvious peak fake photons increase:~10% a peak around 70MeV Fake photon energy in EMC π- (momentum=100~500MeV) Deng Ziyan, IHEP

  15. Magnetic Field From SMG • Uniform magnetic field being used • Simulation and reconstruction can use the same 3D magnetic field. • Linear interpolated algorithm has been checked carefully and works well Y=0 plane From BOSS Deng Ziyan, IHEP

  16. MDC Drift distance-> drift time dE/dx Wire resolution added noise added TOF Light emission & light propagation PMT response & threshold discrimination EMC Waveform added Simulate main amplifier output Provide risetime to eliminate noise MUC Strip ID Noise added Digitization Deng Ziyan, IHEP

  17. MC truth • Purpose • To provide truth information for reconstruction and physics analysis • What to save • True state of the particles and their association with detector response • Particle • particles from generator • uninterrupted decayed daughters • Detector response • hits in sub-detectors associated with particles Deng Ziyan, IHEP

  18. Track and vertex (associated with particle) Track PDGcode charge original vertex terminal vertex four-momentum decayed daughters Vertex parent track position time truth hits (associated with track) Considering demand of each reconstruction developer MDC Hit history TOF First-hit EMC Total energy loss MUC Hit history MC truth Deng Ziyan, IHEP

  19. Data I/O • Output MCtruth and raw data in two formats • ASCII format (simple, convenient, but big size) • Binary format (just as online, small size, for large sample) • Easy for user to choose data format • Easy to turn on/off • EVHEAD • TRACKTRUTH, VERTEXTRUTH • MDCTRUTH, MDCDIGI • TOFTRUTH, TOFDIGI • EMCTRUTH, EMCDIGI • MUCTRUTH, MUCDIGI Deng Ziyan, IHEP

  20. Trigger simulation Trigger Table jobOptions Event Filter Output Files Trigger Algorithm Trigger Service Mdc Trigger Conditions (Total 9 conditions) Mdc Digi Mdc Track Segment Finder Track Finder Global trigger Isolated Cluster Emc Trigger Conditions (Total 16 conditions) Emc Digi Emc Trigger Cell Energy Sum and Balance Tof Trigger Conditions (Total 6 conditions) Tof Digi Tof Hit Count • Trigger simulation with three sub-detectors almost completed • Trigger with Muc is ongoing • Cross check has been made with trigger group Deng Ziyan, IHEP

  21. Background Mixing • Event mixing (developed by Dubna group) • Signal + Background  Real event • Algorithm implemented • Only signals and noise with the same identifier are added up • If no corresponding MC digit found, new digit is created with background information • New charge is sum of MC charge and background charge • New time measurement is the earliest of two • These rules can be changed individually for each sub-detector, if requested Deng Ziyan, IHEP

  22. Background Mixing Simulated background Trigger group did some study on this … MC background events are used for mixing Background data taking There were some discussions … Single beam, or separated beams without collision Data taking with random trigger Deng Ziyan, IHEP

  23. Performance: speed • Average 0.9 second per physics event • About 1.5 times slower than BESII simulation (G3) Responsible: J. Apostolakis / G. Cosmo Description: "Compared to G3 simulation, under similar circumstances G4 is reported by the LHC experiments, to be a factor 1.5-2 slower. A study group started last year to address this issue, and should continue with more priority. This is expected to be a collaboration between G4 and the users." Geant4 Technical Forum on November 20th, 2006 Deng Ziyan, IHEP

  24. Performance: MDC μ- at pt = 1GeV/c spatial resolution: ~110µm momentum resolution: ~0.4% Deng Ziyan, IHEP

  25. Performance: TOF time resolution at z=0: 85ps (1GeV electron) beta vs momentum (e, µ,π, K, p) Deng Ziyan, IHEP

  26. Performance: EMC energy resolution of gamma: 2.1%@1GeV spatial resolution of gamma: 5.8mm@1GeV Deng Ziyan, IHEP

  27. Performance Deng Ziyan, IHEP

  28. Summary • Simulation software running stably • Key quantities consistent with design target • Mass production starts for physics study • More studies on physics processes and digitization needed Deng Ziyan, IHEP

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