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

2. April 24, 2007Deng Ziyan, IHEP2 Outline  BESIII experiment  BESIII offline software  Simulation Algorithm  Performance  Summary

3. April 24, 2007Deng Ziyan, IHEP3 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: ▪1.0×10 31 cm -2 s -1  1.0×10 33 cm -2 s -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 

4. April 24, 2007Deng Ziyan, IHEP4 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

5. April 24, 2007Deng Ziyan, IHEP5 BESIII Offline Software System BOSS Transient Data Store Generator Simulation Digitization Gaudi Event Display Simulation Reconstruction Physics Analysis Calibration Cal-MDC EVERTEX EMC(B/E) V0FIND Exp. data MC data Detector-Geo Cal-Data Control-Data DST Made Cal-TOFFast-trackEvent-T0 MUIDTOF(B/E)MDC-track REC Data DST Data Pre-tracking Post-tracking Phy-tracking calibUtil Services Register, write Search Read Gaudi Client Calibrator Gaudi services Metadata (persistent) MySQL rdbms FACS Calibration & Database Simulation Reconstruction

6. April 24, 2007Deng Ziyan, IHEP6 Simulation Algorithm  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 Project Leader: Liu Huaimin Cao Guofu, Deng Ziyan, He Miao, Liang Yutie, Pan Minghua, You Zhengyun, Yuan Ye

7. April 24, 2007Deng Ziyan, IHEP7 Detector Description xy (z=0)yz (x=0)

8. April 24, 2007Deng Ziyan, IHEP8 Detector Description MDC EMC TOF MUC stereo cell: G4TwistedTub G4IrregBox

9. April 24, 2007Deng Ziyan, IHEP9 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

10. April 24, 2007Deng Ziyan, IHEP10 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. Classes for Simulation Geometry, Materials, Alignment… XML description Classes for Reconstruction Classes for Event Display ROOT Schema XML writer GEANT4 Schema

11. April 24, 2007Deng Ziyan, IHEP11 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?

12. April 24, 2007Deng Ziyan, IHEP12 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

13. April 24, 2007Deng Ziyan, IHEP13 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

14. April 24, 2007Deng Ziyan, IHEP14 a peak around 70MeV no obvious peak fake photons increase:~10% Energy(GeV) Old: Geant4.7.1New: Geant4.8.1+p01 Fake photon energy in EMC π- (momentum=100~500MeV) Hadronic Models (QGSP)

15. April 24, 2007Deng Ziyan, IHEP15 Y=0 plane From SMG From BOSS Magnetic Field  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

16. April 24, 2007Deng Ziyan, IHEP16 Digitization  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

17. April 24, 2007Deng Ziyan, IHEP17 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

18. April 24, 2007Deng Ziyan, IHEP18 MC truth  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

19. April 24, 2007Deng Ziyan, IHEP19 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

20. April 24, 2007Deng Ziyan, IHEP20 Trigger simulation Tof Digi Mdc Digi Mdc Track Segment Finder Track Finder Mdc Trigger Conditions (Total 9 conditions) Emc Trigger Cell Energy Sum and Balance Isolated Cluster Emc Trigger Conditions (Total 16 conditions) Tof Hit Count Tof Trigger Conditions (Total 6 conditions) Trigger Service Global trigger jobOptionsEvent Filter Trigger Algorithm Emc Digi Output Files Trigger Table Trigger simulation with three sub-detectors almost completed Trigger with Muc is ongoing Cross check has been made with trigger group

21. April 24, 2007Deng Ziyan, IHEP21  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 Background Mixing

22. April 24, 2007Deng Ziyan, IHEP22 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

23. April 24, 2007Deng Ziyan, IHEP23 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."

24. April 24, 2007Deng Ziyan, IHEP24 Performance: MDC spatial resolution: ~110 µm momentum resolution: ~0.4% μ - at p t = 1GeV/c

25. April 24, 2007Deng Ziyan, IHEP25 Performance: TOF time resolution at z=0: 85ps (1GeV electron) beta vs momentum (e, µ,π, K, p)

26. April 24, 2007Deng Ziyan, IHEP26 Performance: EMC energy resolution of gamma: 2.1%@1GeV spatial resolution of gamma: 5.8mm@1GeV

27. April 24, 2007Deng Ziyan, IHEP27 Performance Sub-detectorDesignedMC MDC spatial 130um 130  m(smeared as designed) 110  m(smeared based on beam test) momentum 0.46%@1GeV 0.46%(  xy =130  m) 0.41%(  xy =110  m) dE/dx 6-7%6% TOF time 80-90ps85ps EMC energy 2.5%@1GeV2.1% spatial 6mm@1GeV5.8mm MUC µ ID 95%96% π miss_ID 6%6.2%

28. April 24, 2007Deng Ziyan, IHEP28 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