Difference: SWGuideIterativeTracking (8 vs. 9)

Revision 92012-11-01 - KevinStenson

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META TOPICPARENT name="SWGuideTrackReco"

Iterative Tracking

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  clusterRemovalInfo = 'secClusters' )
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 The 4_4_X default tracking in CMS contains 7 iterations, labeled 0 through 6. These correspond to algo values 4-10. 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
InitialStep (0) pixel triplets 0.6 0.03 4.0σ
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MixedTripletStep (4) Triplets: pixel, TIB1,2, TEC ring 1,2, wheels 1-3 0.35-0.5 2.0 10.0
PixelLessStep (5) Pairs: TIB1,2 & TID/TEC ring 1,2 0.6 2.0 10.0
TobTecStep (6) Pairs: TOB1,2 & TEC ring 5, wheels 1-7 0.6 6.0 30.0
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The 5_X_X default tracking in CMS contains 7 iterations, labeled 0 through 6. These correspond to algo values 4-10. 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
InitialStep (0) pixel triplets 0.6 0.02 4.0σ
LowPtTripletStep (1) pixel triplets 0.2 0.02 4.0σ
PixelPairStep (2) pixel pairs 0.6 0.015 0.09cm*
DetachedTripletStep (3) pixel triplets 0.3 1.5 15cm
MixedTripletStep (4) Triplets: pixel, TIB1,2, TEC ring 1,2, wheels 1-3 0.4-0.6 1.5 10cm
PixelLessStep (5) Pairs: TIB1,2 & TID/TEC ring 1,2 0.7 2.0 10cm
TobTecStep (6) Pairs: TOB1,2 & TEC ring 5, wheels 1-7 0.6 6.0 30cm
  In the table, d0 and z0 refer to the transverse and longitudinal impact parameters of seeds with respect to the beamspot. 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 for higher pT (iteration 0) and lower pT (iteration 1), followed by pixel pairs (iteration 2) for additional efficiency. Iteration 3 uses pixel triplets like iterations 0,1 but searches for displaced tracks. Iteration 4 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 0-4 and 6 for iterations 5-6), the number of lost hits (1 for iterations 0-3 and 0 for iterations 4-6). 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 can be found by looking in the configuration steps which are linked in the table above and annotated more below.
 
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