The status of Track Extrapolation module Wang Liangliang 2005.6.29

Introduction In reconstruction,in order to associate the hits in outer detectors(e.g. mu counter) with MDC reconstructed tracks,we need track extrapolation. In these applications,the credibility and the evaluations of the track's errors are important. So I developped an algorithm named TrkExtAlg in BOSS to do this work,which mainly reference to BELLE’s corresponding work.

TrkExtAlg extrapolate MDC reconstructed tracks to outer detectors,which takes account of energy loss of particles and the magnetic field.That is why it base on GEANT4. TrkExtAlg’s another job is giving error matrix of position and momentum of a extrapolated track. In fact multiple scattering errors dominate. So TrkExtAlg also propagates of error matrix which takes account of multiple scatterring effect.

TrkExtAlg Class Ext_track is the one which is in charge of extrapolation of tracks in fact. TrkExtAlg is an interface of Ext_track to BOSS. GEANT4 Transient Event Data Store base on MDC reconstructed tracks Track extrapolation TrkExtAlg Ext_track Error calculation Track extrapolation results and error matrixes

initialize() GeometryIntialization() Ext_track->Initialization(myExtPar) PhysicsIntialization() Get MDC reconstructed tracks Called once every event. Loop over every track in an event. Ext_track->Set(x,p,err,ParticleName) TrkExtAlg execute() ExtTrack->TrackExtrapotation() Write results to TDS finalize()

Geometry Initialization BesDetectorConstruction(…) Geometry, material, magnetic field…… (Now, it comes from BOOST.) (In future, it will be construct from xml files.) Some other needed…… Compared with GEANT4 simulation,mine is simple,just what I need.Same is physics initialization.

Physics Initialization Particle Definition e mu K pi p photon Physics Processes Energy loss Ionisation (Modified) Bremsstrahlung (e mu) Build physics table ……

Track Extrapotation According to the information of MDC tracks,I initialized a G4Track.(default particle type is pi) As long as geometry and physics initialization is done,G4TrackingManager can work. Then this track is transported step by step by G4TrackingManager which uses G4SteppingManager with responsibility for each step. After every step in GEANT,my ExtSteppingAction() will be called.

What does ExtSteppingAction() do? Getting track information,and judging whether the particle enters a new volume,if so,following things will be done: Error matrix calculation. Update some coefficients according to current material,which will be used in error calculation. If current track information will be needed in reconstruction , these parameters will be tacken down and be writen to TDS.

Error Matrix 1.Error propagation: 2.Add multiple scattering error :

double Ext_errmx::get_plane_err( const Hep3Vector &np, const Hep3Vector &nr )

Some results Ext: track extrapolation (TrkExtAlg based geant4.6.2) Sim1: G4MultipleScatterring, G4hIonisation (TrkExtAlg based geant4.6.2) Sim2: boost-1-2 based geant4.6.2 Reference surface (cylinder) (R,phi,z) R=810mm ~ TOF R=942mm ~ BSC R=1375mm ~ Superconducting magnet R=1700mm ~ MUC

1200MeV pi- theta=90 phi=0 (0,0,1mm) Ext Sim1 Sim2 R 810 0.1070 0.0012 1 0.92 0.1073 0.0015 0.99 0.95 0.97 942 0.1231 0.0014 1.3 0.1233 0.0017 0.98 1.4 1375 0.1782 0.012 16 0.010 0.86 14 0.013 0.70 1700 0.2188 0.019 32 0.2190 0.018 0.45 29 0.2193 0.023 -0.4778 33

1200MeV pi- theta=60 phi=0 (0,0,0) Ext Sim1 Sim2 R 810 0.1234 0.0015 468.8 1.4 0.1232 0.0018 468.7 1.5 942 0.1422 0.0017 545.6 1.9 0.1418 0.0020 545.5 2.0 0.1419 2.1 1375 0.2062 0.014 799.3 22 0.2060 21 0.2063 0.017 799.1 26 1700 0.2536 0.023 991.6 44 0.2541 991.9 0.2545 0.030 990.2 56

1200MeV pi- theta=45 phi=0 (0,0,0) Ext Sim1 Sim2 R 810 0.1511 0.0019 812.8 2.2 0.1498 0.1499 0.0023 2.4 942 0.1741 946.4 3.1 0.1728 946.3 3.3 0.1729 0.0028 3.5 1375 0.2534 0.018 1389 35 0.2532 1391 32 0.2524 0.023 1388 42 1700 0.3121 0.029 1726 68 0.3119 0.028 1730 66 0.3093 0.035 1720 83

600MeV pi- theta=90 phi=0 (0,0,1mm) Ext Sim1 Sim2 R 810 0.2118 0.0022 1 1.8 0.2115 0.0026 0.98 2.0 0.2114 0.0025 1.01 942 0.2451 2.5 0.2447 0.0031 0.97 2.8 0.0032 1.03 2.9 1375 0.3650 0.030 38 0.3651 0.027 1.31 34 0.3640 0.65 36 1700 0.4662 0.048 77 0.4654 0.050 1.5 76 0.4612 0.056 0.51 81

600MeV pi- theta=60 phi=0 (0,0,0) Ext Sim1 Sim2 R 810 0.2455 0.0027 472.2 2.5 0.2437 0.0032 472.0 2.9 472.1 942 0.2842 0.0033 550.9 3.6 0.2824 0.0039 550.7 4.2 0.2825 0.0040 550.8 1375 0.4260 0.036 819.1 53 0.4254 0.034 820.2 49 0.4243 0.038 818.5 54 1700 0.5475 0.057 1035 105 0.5484 0.064 1037 109 0.5415 0.072 1024 125

600MeV pi- theta=45 phi=0 (0,0,-500mm) Ext Sim1 Sim2 R 810 0.3010 0.012 322.1 14 0.3020 0.016 322.2 18 0.3030 329.6 942 0.3505 0.013 461.1 17 0.3514 0.017 22 0.3525 469.7 23 1375 0.5495 0.061 956.0 108 0.5469 0.063 952.0 101 0.5429 0.075 942.5 114 1700 0.7577 0.10 1412 221 0.7205 0.12 1343 200 0.6888 0.13 1251 223

Summary Generally saying, the differences between Ext and Sim is under 20 persent. When momentum of particle becomes smaller or cos(theta) becomes larger, the difference will be larger. TrkExtAlg needs to be more accomplished.

Something about PID Charged particle: e , mu , pi , K ,p/pbar TOF,MDC(dEdx): pi , K , p/pbar Method: Likelihood Get pure pi, K, p/pbar TOF/DEdx normalized distribution(histogram) at different momentum.(MC/True data) According to measured data (momentum,TOF/DEdx), we can get corresponding probability through the distribution in 1. Define:

Thank you!