1. The status of Track Extrapolation module
Wang Liangliang

2. 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.

3. 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.

4. 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

5. 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()

6. 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.

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

8. 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.

9. 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.

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

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

12. 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

13. 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 33

14. 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

15. 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

16. 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

17. 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

18. 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

19. 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.

20. 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:

21. Thank you!