Presentacin de PowerPoint

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Status of ITS stand-alone tracking reconstruction
(grouping algorithm)
Elisabetta Crescio INFN-Torino March, 2004

• Several months for debugging and optimization
• Code Submitted to CVS on December 2003
• AliITStrackerSA, AliITStrackSA,
  AliITSclusterTable
• Compatible with V2
• February 2004 integration in ESD - included in
  the reconstruction for PDC04

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Track Finding (1)
Method inspired by the grouping algorithm
described in ALICE/ITS 99-34 Tracking of the
high Pt particles in ITS stand-alone detector,
P. Kindziuk, P. Lesczynski, A. Maliszewski, J.
Mazur, J. Pluta, A. Roszczewski, H. Gutbrod and
optimized for tracks with pT lt 1 GeV/c. Working
space (?,?) plane Iterative procedure high
pT tracks are found first, and their associated
points are eliminated. Tracks with decreasing
momentum are successively found.

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Track Finding (2)
Y
Basic idea
Use of vertex -gt primary tracks
expected ?
Algorithm procedure
For each couple of points of layer 1 and 2 in a
(?,?) window the curvature of the candidate
track is evaluated using the vertex information.
The expected value of ? on the next layer is
evaluated and it is considered as center of the
(?,?) window on next layer. The precedure is
repeated for all layers. Several loops increasing
the window size and eliminating the points
associated to found tracks.
vertex
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Track Fitting
Fit with Kalman filter Seeding helix
fit with AliITSRiemannFit (by R. Turrisi,..)
on the points of layer 1,2 and using the vertex
to have initial parameters of the track.
Fit Function RefitAt of AliITStrackerV2
from vertex to layer 6 and back
from layer 6 to vertex. Since a
candidate track can have more than 6 associated
points, the fit is performed on all possible
combinations of points and the reconstructed
track with lower ?2 is chosen. Final tracks are
AliITStrackV2 objects or AliESDtrackkITSin
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Tracking algorithm efficiency
evaluated for
Hijing 4000 Hijing 6000
ITS only (6/6)
ITS only (5/6)
combined with TPCITS V2
magnetic field 0.4 Tesla
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Hijing 4000 ITS only 6/6
Trackable one cluster for each layer of the ITS
(6/6)
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Hijing 4000 ITS only 5/6
Trackable one cluster in 5 layer of the ITS (5/6)
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Hijing 4000 - Combined tracking
Trackable one cluster for each layer of the ITS
(6/6)
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Hijing 6000 ITS only 6/6
Trackable one cluster for each layer of the ITS
(6/6)
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Hijing 6000 ITS only 5/6
Trackable one cluster in 5 layer of the ITS (5/6)
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Hijing 6000 Combined tracking
Trackable one cluster for each layer of the ITS
(6/6)