Material budget, energy losses and multiple scattering

1. Material budget, energy losses and multiple scattering

2. Barrel tracking • Momenta resolution for low momenta tracks determined mainly by energy losses and multiple scattering • Left side – momentum resolution for pion • Right side - proton

3. Energy loss between vertex and TPC • Left - rel. loss as a function of particle velocity • Right – function of particle momenta

4. Energy losses (Bethe Bloch) • b -particle velocity • r - material density • Z - atomic number of absorber • A – mass number of absorber • I – mean excitation energy • d – density effect correction factor – material dependent and b dependent

5. Energy losses (Reconstruction) • b - particle velocity • r - material density • K1 and K2 – Effective parameters

6. Energy loses correction • Left side - correction shift as function of particle velocity • Right side – correction shift as function of particle momenta (pion)

7. Energy loses correction • Left side - correction shift as function of particle momenta (kaon) • Right side – correction shift as function of particle momenta (proton)

8. Multiple scattering (Gaussian approximation) • b -particle velocity • r - material density • P - particle momenta

9. Energy losses correction (Current) • Material budget and radiation length hardwired in the code • Using symmetry of the detectors • Correction layer by layer during propagation • Intervals in y and z in the local coordinate frames • Fast access • Difficult to describe non symmetric parts (big problem in TRD)

10. Geo modeler (0) • Used to get information necessary for energy loss calculation and multiple scattering • Local information - in each point density, radiation length, Z, A defined (mean excitation energy missing) • Mean query time ~ 15 ms • Mean number of queries • ~15 – between 2 ITS layer • ~15 – between 2 TRD layers

11. Geo modeler (1) • Two option considered • 1. Propagate track up to material boundary defined by modeler – get local material parameters • Time consuming - too many propagations • 2. Calculate mean parameters between start and end point • <density>, <density*Z/A>, <radiation length> • Faster (only one propagation), reusable in the case of parallel hypothesis (ITS), not big changes in the tracking

12. Implementation • AliKalmanTrack::MeanMaterialBudget(Double_t *start, Double_t *end, Double_t *param) • First test • Track references in inner volume of the TPC – propagated to the vertex

13. TRD tracking • FollowProlongatioBackG implemented • Using mean material budget • 14 steps • Propagate to first plane • Loop over TRD planes • Propagate and update in the sensitive layer • Propagate to the next plane • Propagate to the outer volume of TRD

14. Energy loss estimate resolution • Left side - old propagation • Right side – new propagation

15. Relative Pt resolution • Left side - old propagation • Right side – new propagation

16. Relative Pt resolution • Left side - old propagation • Right side – new propagation

17. Pt pulls • Left side - old propagation • Right side – new propagation

18. Time pulls • Left side - old propagation • Right side – new propagation

19. Conclusion • First results in TRD tracking • Indication of improvements in the momentum and the time resolution • Test with propagation to the vertex using AliExternalParameter and GeoMedeler – better vertex position resolution • Better interface required – without user intervention

20. Conclusion • Default access to the TGeoManager required • Currently loaded by hand • Better energy loss parameterization- options: • 1. Mean Energy loss and multiple scattering calculation using TGeoManager • 2. Tuning 1 free parameter -