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## Track Reconstruction in MUCH and TRD

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**Track Reconstruction in MUCH and TRD**Andrey Lebedev 1,2 Gennady Ososkov 2 CBM Collaboration Meeting October 13-18, 2008 Dubna, Russia 1Gesellschaft für Schwerionenforschung, Darmstadt, Germany 2Laboratory of Information Technologies, Joint Institute for Nuclear Research, Dubna, Russia**Track propagation fundamentals**Track propagation algorithm transports the track in terms of its meanvalues and corresponding errors. The basic element of the extrapolation is the transport matrix: Track propagation algorithm transports the track in terms of its meanvalues and corresponding errors. Extrapolation of the covariant matrix: Dividing extrapolation into n steps, the transport matrix is calculated as a consecutive multiplications of transport matrices for each step: State vector Covariance matrix**Track propagation algorithm**• Extrapolation. Two models: • Straight line in case of the absence of the magnetic field. • Solution of the equation of motion in the magnetic field with the 4th order Runge-Kutta method, with a parallel integration of the derivatives. • Material Effects. • Energy loss (ionization: Bethe-Bloch, bremsstrahlung: Bethe-Heitler, pair production) • Multiple scattering (Gaussian approximation) • Navigation. • Based on the ROOT TGeoManager. The Algorithm: Trajectory is divided into steps. For each step: Straight line approximation for finding intersections with different materials (geometry navigator) Geometrical extrapolation of the trajectory Material effects are added at each intersection point**Track fitter**• Forward Kalman filter • Sequence of prediction and update operations • Backward Kalman Smoother • Estimations based on all the hits in the track, using Kalman smoother equations • Iterative KF fit with outlier removal • Consecutive applications of the forward and backward track fitters • After the backward fitter the chi-square of the hit is used to identify the outliers.**Track finding**• Based on the track following and the Kalman filter methods. • Uses branching. Branch is created for each hit, passed the test to be assigned to the track segment and for the missing hit. • Initial seeds: • MUCH: tracks reconstructed in STS. • TRD: track reconstructed in STS or standalone. The main components of the track finding algorithm are track following and track selection.**Track finding**• Track selection • Tracks are sorted by their quality, obtained by chi-square and track length • Check of the shared hits procedure is executed Check of the shared hits - Remove clone tracks, i.e. track that -have similar set of hits**Test setups**MUCH Compact MUCH Standard MUCH Compact:5Fe absorbers (125 cm) 10 detector stations Standard:6 Feabsorbers (225 cm) 18 detector stations TRD Standard: 12 detector layers, grouped in 3 stations**Verification of the energy loss for muons in iron**total ionization pair production bremsstrahlung D.E.Groom, N.V.Mokhov and S.I.Striganov, Muon stopping power and range tables 10 MeV-100 TeV, Atomic Data and Nuclear Tables, 78, 2001 table Energy loss for muons in iron Lit**Verification of the multiple scattering**Theta angle of the multiple scattering for muons passing 10 cm of iron**Performance of the track propagation**Simulated data: 100k mu+ and mu- with momentum range 1-10 GeV/c. Track parameters are updated with the Kalman filter on each station. Pulls X Y Tx Ty Residuals Bold –sigma of the Gauss fit, (in brackets) – RMS value. F – first, M – middle, L – last station Pulls**Performance of the track finder in MUCH**Compact Standard Events: URQMD central Au+Au at 25 AGeV + 5 mu+ and 5 mu- in each event (p=1.5..10 GeV/c for compact p=2.5..25 GeV/c for standard)**Performance of the track finder in TRD**Events: URQMD central Au+Au at 25 AGeV + 25 e+ and 25 e- in each event (p=1..10 GeV/c)**Summary**• The design of the Lit track reconstruction package has been improved which lead to easier support and better flexibility • Track selection algorithms has been considerably improved • The track propagation algorithm has been improved: • More accurate calculation of the material effects • Usage of TGeoManager for navigation • Stepping • Compare to GEANE