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Status of BESIII Event Reconstruction System

This system provides event reconstruction for the BESIII experiment, including drift chamber tracking, superconducting magnet, TOF system, muon chamber, EMC, and offline software.

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Status of BESIII Event Reconstruction System

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  1. Status of BESIII Event Reconstruction System BESIII offline software group 2006.10.31

  2. BESIII Experiment Main Drift Chamber (MDC)： xy = 130 m P/P = 0.5 %@1 GeV dE/dx = 6-7 % Super-conducting Magnet：1.0 Tesla TOF System： T = 90 ps barrel 110 ps endcap Muon Chamber (MUC)： RPC based EM Calorimeter (EMC)：E/E = 2.5 % @ 1 GeV 　 z, = 0.6 cm @ 1 GeV

  3. Offline software BOSS – BES Offline Software System based on Gaudi.

  4. Reconstruction algorithm Simulation algorithm GUI Client MySQL database CalibFunc Svc CalibRoot CnvSvc Calibration Algorithm Calibration Data Service Calibration constants (ROOT) Calibration • Recon. and simulation algorithms retrieve calibration data from calibration data store • Calibration constants are stored in ROOT files

  5. The BESIII Event Reconstruction Modules and General Flow EventStartTime (Fast-tracking, PID,EST ) MDC Tracking EventStartTime dE/dx Rec. (Particle ID) Track Fitting (Kalman Filter) Track Ext. Track Matching TOF Rec. EMC Rec. MuC Rec. Veefind Evtvert

  6. MDC Fast Tracking Module Track parameters: d0, Ф0, Κ, dz, tgλ

  7. TEST (Event Start Time) Module The TEST is important for the momentum Res., spatial Res. of the charged particles, but it is uncertain in the online system due to: 1) The BESIII trigger system can’t separate every event up to beam bunch. 2) The start time of charged event is determined by TOF_T, but the TOF reach time is different for different particle and different momentum. TEST should be calculated by offline system. REF (2ns) Bunch (8ns) Trigger Clock (24ns) TOF tev Test TDCM(TOF) MDC TDCM(MDC)

  8. TEST (Event Start Time) Flow • Calculate Testby • straight line segments fit MDC Fast Reconstruction PID Have TOF Information ? TOF NoTOF No Yes MDC Fast Rec. Information? No 2.Calculate TestbyTOF Inf. And MDC Fast tracking Inf. Yes 4. Calculate Test Only by MDC Inf. 3. Calculate Test by MDC Inf. And Fast tracking Inf. Yes

  9. Preliminary Result ofTEST Segment Fit Test Eff. : 100% TOF: 96.78% MDC: 3.22% Muon ,Test=0ns,8ns,16ns, 5000 events TOF: 97.2% MDC: 2.6% Segment Fit: 0.2% Test Eff. : 96.4% error：0.63% e+e-hadrons ,Test=0ns,8ns,16ns, 5000 events

  10. Mdc Tracking Algorithm Two algorithms for MDC track reconstruction: TrkReco&MdcPatRec

  11. MDC Tracking Module(1) (based on Belle Lib.) • Init:Geometry-Survice., Cal.-Const., Adjust-constant Get Hit Information… • R- Tracking:segment finding byconformal transformationandhistogram method Conformal transformation • Z Finding • 3D Helix Fit S-Z calculation in Z finding

  12. 7 6 5 4 3 2 1 0 1 7 6 0 0 5 1 4 3 0 2 1 0 1 1 0 MDC Tracking Module(2)(based on Babar Lib. ) • Init:Geometry-Survice., Cal.-Const., Adjust-constant Get Hit Information… Sequence of segment Finder For every superlayer, every wire in 2nd Layer form a group of 8 wires • Segment finding: Search segments in each super-layer using a pattern look-up table Wires No. 0-7 For every group  Set one word for a group of 8 wire, each bit for a wire.  Set “1” for a hit wire, others “0”  This octal value used for its group No. (1) Try 4 hit pattern for group • Tracking:Link segments to 2D tracks, add stereo segments (2) Try 3 hit pattern for group Set massage of segment list • 3D Helix Fit

  13. Preliminary Result of MDC tracking Momentum resolution μ- at pt = 1GeV Momentum resolution σp = 0.40% Spatial resolution μ- at Pt = 1GeV spatial resolution σ ~=110μm

  14. Preliminary Result of MDC tracking Efficiency vs Pt (e-,μ-,π,p) d0: signed distance from the pivot to track in x-y plane  0.1 mm z0: signed distance from the pivot to track in z direction  0.8 mm • Efficiency > 95% for single track Pt > 200MeV

  15. Kalman filter tracking fitting Module The MDC reconstruction results are not very good, have to do KalFit: • multiple scattering • energy losses • non-uniform magnetic fields • …… Parameters of a track before KalFit & after KalFit(proton 300Mev)

  16. Principle: P =βγ· m dE/dx Module Particle type info dE/dx~f(v) MDC tracking • dE/dx codes developed successfully, released for physics study. • Particle ID is tested with MC samples, dE/dx resolution, distributions, PID efficiency is reasonable.

  17. Pre. Performance of dE/dx dE/dx seperation for 5 particles(MC) seperation power with dE/dx • Good particle seperation in a wide range for different particles • The π/K seperation(3 σ ) reach about 800 MeV/c • Particle identification efficiency is more than 90% with MC samples

  18. Track Extrapolation Module Function:Extrapolate MDC tracks to Outer detectors: TOF, EMC and MUC Algorithm:based on GEANT4, Energy loss and Magnetic field. Multiple scattering effect put into error matrix.

  19. TOF Reconstruction Module Geometry data TofGeomSvc Data base Initialize() Calibration constants TofCalibSvc Tof Digits Get Data TDS MDC Tracks Get Tracks Make Hits execute() Match Hits and Tracks Tof Tracks TDS Reconstructed Tof Tracks finalize()

  20. Primary TOF Recon. Result • Reconstruction Efficiency : 99.82% (1 GeV electron data) beta vs momentum time resolution:113ps

  21. EMC Reconstruction Module EMC is used to measure energy and position of electrons and photons, and to provide neutral energy trigger digit hit shower cluster

  22. Pre. Performances of EMC single gamma with 0.5MeV noise σE/E≈2.2%@1GeV theta Recon Effi. of π0 phi

  23. Searching hits gap by gap; Window Fired strips Searching on Barrel first, then EndCap; Also Searching on neighboring segments; Line Fit with hits on track; Ext track Barrel End Cap Muc Reconstruction Module Use Ext Track from Mdc as seed; Compare with Mc truth;

  24. μefficiency π(fake μ ) Pre. Performances of Muc μ/πIdentifcation Ratio % With different θ 90 70 50 40 30 p (GeV/c)

  25. Summary • Based on Gaudi, the BESIII offline software system (Boss) has developed • Simulation • Reconstruction • Calibration system • Physics analysis • All sub-system work well on the Boss 6.1.0, got the Pre. Performance by the simple data sample, and passed the checking by typical physics channel. • More works need to do to make each code work in the best status by closely the data to real data case step by step, such as: “noise study”, NUMF and “low momentum tracking” and S-T relation in MDC etc. • Data challenge and software performance optimization are the major task in the next step.

  26. Thank you ！

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