1. New TRD (&TOF) tracking algorithm
Marian Ivanov, Alice Offline week

2. TRD tracking TRD tracking changes - improvements
Cluster search mechanism replaced with tracklet search mechanism
Chi2 minimization for full tracklet not for separate clusters
Advantage in high flux enviroment
New cluster error parameterization
Alignment using reconstructed tracklets
Kalman filter (Important for low momenta tracks):
Energy loss fluctuations taken to the account (covariance)
Increasing of the multiple scattering coefficient
Ongoing work on improvement for low momenta tracks – important for TOF matching

3. New cluster tracklet search mechanism
Previous version:
Cluster with minimal chi2 to predicted track position taken
Problem
Track possition uncertainty comparable with mean distance between clusters
Possibility to take non proper cluster

4. New cluster tracklet search mechanism (0)
New version
Looking for tracklets (set of clusters at given plane) with minimal chi2
Tracklet position and angle taken to the account
Minimize the number of changes in pad-rows
Maximum 1 change possible (tan(theta)*3cm<padlength)
Problem: too many clusters in the road
Tree building too slow
Sollution – Iterative search

5. New cluster tracklet search mechanism (1)
Iterative search:
1 approximation - closest clusters to the track taken {
Tracklet position, angle and their uncertainty calculated
Weighted mean position calculated (tracklet+ track)
If chi2 of current tracklet smaller than chi2 of best previous and the number of pad-row changes less or equal of best previus – make current tracklet best
Closest clusters to the weighted mean taken }

6. New cluster tracklet search mechanism - r-phi direction(2)

7. New cluster tracklet search mechanism - z direction(3)

8. Cluster error parameterization
Base cluster position fluctuation
Estimated using RMS of tracklet clusters residuals
Sigmay2 = RMS
Uncertainty corresponding to collective shifts of tracklet added to all clusters
Correction for unisochronity and width of the Time Response Function
Sigmay2 += (sigma(dt)*tan(phi))^2*N(cluster)
Additional penalty factor for mean number of pads per cluster and number of pad-rows changes
Effective correction for unfolding

9. Cluster error parameterization
Left column - cluster residuals to the track-let interpolation
Right column – track-let residuals to the Kalman track extrapolation

10. Pulls pt

11. Pulls z

12. Pulls y

13. Pt resolution

14. Pt resolution

15. Alignment Following alignment coefficient extracted using tracklets
Effective drift velocity (factor ~1.07)
X0 (time 0) offset (~ 3 mm)
Y0 offset (~0.12 mm)

16. Alignment (effective drift velocity)

17. TRD tracking at high flux environment (central event dN/dy~5000)

18. TRD tracking at high flux environment (central event dN/dy~5000)

19. TOF matching Key role of the TRD tracking
Goal improve space resolution for TOF
Provides probability information is track still alive
~66 % of fake TOF information because the track not alive anymore (decayed or absorbed in material)
Information track still alive – current implementation
Given by the weighted chi2 of tracklets – weight increase close to the TOF

20. Y resolution

21. Z resolution

22. Y pulls

23. Z pulls

24. New TOF matching (0)
The pad “probability coverage” (probability that track cross given pad) in y and z direction as a function of the distance to the pad center
Integral of Gaussian distribution of possible track prolongations

25. New TOF matching (1) Cut on probability coverage depends
Depending on the TRD information – track still alive
Cluster with biggest probability coverage taken by default
If the probability coverage for two cluster close each other –additional information about time distance (TOFtdc – TOFkalman) used
Better solution – TOF PID probability sum of conditional probabilities (under investigation)
TOF PID has to be assigned to the track during tracking when all possible prolongations are available

26. Conclusion The pt resolution for high momenta tracks improved
Theoretical limit reached
critical for alignment TRD performance
Alignment better than 0.1 mm required
Ongoing work on tracking for low momenta tracks
Improve space point resolution in y
New development of cluster finder
Provides probability information – track still alive
TOF matching algorithm
Under development
Beta version – efficiency increase by 13 %, fake ratio decreased
Need another TOF PID schema
Don’t use AliTOFpidESD class – assign PID during tracking