Difference: SWGuideIterativeTracking (6 vs. 7)

Revision 72011-06-17 - KevinStenson

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META TOPICPARENT name="SWGuideTrackReco"

Iterative Tracking

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  Tracking meeting 23 may 2007
PFlow meeting 05 july 2007
Tracking meeting 01 august 2007
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ParticleFlow meeting 13 september 2007
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CMS.ParticleFlow meeting 13 september 2007
 Tracking meeting 31 january 2008
Tracking meeting 05 february 2008
Tracking meeting 14 february 2008
The results of the iterative tracking are summarized in the internal note 2007/065

Summary of the current iterative steps

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The current (3_1_X) default tracking in CMS contains 6 iterations, labeled 0 through 5. The main distinction between the iterations is the track seeding algorithm which is shown in the table below.
Iteration Seeding Layers pT cut (GeV) d0 cut (cm) z0 cut (cm)
Zero pixel triplets 0.5 0.2 15.9
1 pixel pairs 0.9 0.2 0.2*
2 pixel triplets 0.075 0.2 17.5
3 pixel pairs 0.35 1.2 7.0
4 TIB1+2 & TID/TEC ring 1+2 0.5 2.0 10.0
5 TOB1+2 & TEC ring 5 0.8 5.0 10.0
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The current (4_2_X) default tracking in CMS contains 6 iterations, labeled 0 through 5. The main distinction between the iterations is the track seeding algorithm which is shown in the table below.
Iteration Seeding Layers pT cut (GeV) d0 cut (cm) z0 cut
Zero pixel triplets 0.8 0.2 3.0σ
1 pixel pairs 0.6 0.05 0.2cm*
2 pixel triplets 0.075 0.2 3.3σ
3 Triplets: pixel, TIB1,2, TID/TEC ring 1,2 0.25-0.35 2.0 10.0
4 Pairs: TIB1,2 & TID/TEC ring 1,2 0.5 2.0 12.0
5 Pairs: TOB1,2 & TEC ring 5 0.6 6.0 30.0
 
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In the table, d0 and z0 refer to the transverse and longitudinal impact parameters of seeds with respect to the nominal interaction point. The * indicates the impact parameter with respect to a pixel vertex. Using triplet seeding is much faster and has a lower fake rate than pairs. Therefore, pixel triplet seeding is run first (iteration 0), followed by pixel pairs (iteration 1) for additional efficiency. This is repeated in iterations 2-3 which is optimized to find lower momentum tracks and also tracks which may decay within a couple of cm of the production vertex. Iterations 4 and 5 do not use pixels to seed and are designed to find tracks which are significantly displaced from the beam line or tracks which do not leave sufficient pixel hits to be found in the earlier iterations. Other differences between iterations during track building include the minimum number of hits (3 for iterations 0-2, 4 for iteration 3, and 7 for iterations 4-5), the number of lost hits (1 for iterations 0-2 and 0 for iterations 3-5). The final cleaning stage is also different. The early steps have stricter requirements on tracks originating from the production vertex while the later steps have stricter requirements on the track quality. Details will eventually be found in the tracking note but for now they can be found in the Very Large Impact Parameter Track Reconstruction note or by looking in the configuration steps which are linked in the table above and annotated more below.
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In the table, d0 and z0 refer to the transverse and longitudinal impact parameters of seeds with respect to the nominal interaction point. The * indicates the impact parameter with respect to a pixel vertex. Using triplet seeding is much faster and has a lower fake rate than pairs. Therefore, pixel triplet seeding is run first (iteration 0), followed by pixel pairs (iteration 1) for additional efficiency. Iteration 2 uses pixel triplets like iteration 0 but searches for very low momentum tracks. Iteration 3 uses pixels and strip triplets to find tracks which miss a pixel layer and also tracks which may decay within a couple of cm of the production vertex. Iterations 4 and 5 do not use pixels to seed and are designed to find tracks which are significantly displaced from the beam line or tracks which do not leave sufficient pixel hits to be found in the earlier iterations. Other differences between iterations during track building include the minimum number of hits (3 for iterations 0-3, 6 for iteration 4, and 6 for iterations 4-5), the number of lost hits (1 for iterations 0-2 and 0 for iterations 3-5). The final cleaning stage is also different. The early steps have stricter requirements on tracks originating from the production vertex while the later steps have stricter requirements on the track quality. Details will eventually be found in the tracking note but for now they can be found in the Very Large Impact Parameter Track Reconstruction note or by looking in the configuration steps which are linked in the table above and annotated more below.
 

Usage of the algorithm

In each tracking iteration the user must:
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  • Create new pixel and strip collections with the new cluster collection
e.g.
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import SiPixelRecHits_cfi secPixelRecHits = SiPixelRecHits_cfi.siPixelRecHits.clone(
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import SiPixelRecHits_cfi secPixelRecHits = SiPixelRecHits_cfi.siPixelRecHits.clone(
  src = 'secClusters' )
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import SiStripRecHitConverter_cfi secStripRecHits = SiStripRecHitConverter_cfi.siStripMatchedRecHits.clone(
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import SiStripRecHitConverter_cfi secStripRecHits = SiStripRecHitConverter_cfi.siStripMatchedRecHits.clone(
  ClusterProducer = 'secClusters' )
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Software architecture

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The code for the hit removal is in the package RecoLocalTracker/SubCollectionProducers
Very good examples for the iterative tracking usage can be found in RecoTracker/IterativeTracking
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The code for the hit removal is in the package CMS.RecoLocalTracker/SubCollectionProducers
Very good examples for the iterative tracking usage can be found in RecoTracker/CMS.IterativeTracking
 

Review status

 
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