Difference: LHCbTrackingStrategies (4 vs. 5)

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Tracking strategies used in LHCb

* THIS PAGE IS WORK IN PROGESS, AND PROBABLY STILL CONTAINS MISTAKES AND OMISSIONS, MORE DETAILS/CORRECTIONS ARE TO FOLLOW *

* TODO: *

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  • * add link to pages describing fitting *
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  • * check if there is a good description of track types somewhere (with sketch) *

Tracks are found by different tracking strategies. A tracking strategy is mainly concerned with how tracks are found in the different subdetectors in general, while tracking algorithms specify how tracks are found in detail. This page attempts to give an overview of the different tracking strategies, the algorithms that implement them and the types of tracks resulting from their application. It also lists the input required by algorithms implementing a strategy.

The order in which strategies are discussed respects dependencies among the strategies, so we will not discuss a strategy before we explain where its input comes from. This means that one has to start with the strategies and algorithms that reconstruct tracks from hits rather than those which already need tracks as input. Furthermore, all strategies have been placed in different categories, depending on the type of tracks they produce.

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Once a track is found, it is fitted with a Kalman filter. See LHCbTrackFitting for details.

As a track may be found by different algorithms, or segments of the same track might be available in different track containers on the TES, so there is a clone killing stage which collects tracks from the various locations, selects the best candidate if there are several (whatever that may mean in practice), and writes the resulting combined collection to an output container, per default Rec/Track/Best. This is usually what one uses in the end for physics analyses. The clone killer is described in more detail in section Clone Killer near the end of this page.

 

Velo Tracking

This category contains strategies to find tracks in the Velo (See also this page.).
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  Output: Upstream tracks
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Default Location in TES: Rec/Track/VeloTT

Algorithms:

Clone Killer

Method: By looking at tracks more closely, a clone killer can check if two tracks or segments of tracks are duplicates of each other and chose the "better" track to append it to its output.

Note: some of the algorithms in this section will copy non-clone tracks to an output container, some will only flag clones without creating track containers or modifying the track content of existing containers

Input: various track types

Output: various track types

Default Location in TES: Rec/Track/Best

 Algorithms:
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  • TrackEventCloneKiller: This is the standard clone killer run in our reconstruction jobs. It removes clones by looking at the hit content of tracks; among two clones, the track with more hits is saved to the output location.
  • TrackBuildCloneTable/TrackCloneCleaner: The combination of these algorithms flags clones by comparing track parameters and flagging the lower quality ones as clones for subsequent analysis by adding an info field to the track. This allows to e.g. apply successively harder cuts on clones during an analysis.
 
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