The status of Track Extrapolation module

1. The status of Track Extrapolation module Wang Liangliang 2005.6.29

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)

14. 1200MeV pi-theta=60 phi=0 (0,0,0)

15. 1200MeV pi-theta=45 phi=0 (0,0,0)

16. 600MeV pi-theta=90 phi=0 (0,0,1mm)

17. 600MeV pi-theta=60 phi=0 (0,0,0)

18. 600MeV pi-theta=45 phi=0 (0,0,-500mm)

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!