SLHC Stacked Tracking Tools

In order to assist with the development of the Stacked Tracker concept, a series of tools have been developed.

Some standardised definitions

  • two or more sensors seperated by O(mm) = a stack
  • the sensors within a stack = stack members.
  • a high pT correlation between hits in a stack = a stub
  • two, three, four, ... stacks separated by O(cm)->O(m) = a double, treble, quadruple, ... stack
  • a correlation between stubs in a double, treble, quadruple, ... stack = a tracklet
  • the basic element from which trigger primitives are produced = a station (be that a stack, a double stack, a treble stack,...)

The tools

The strawman b family of upgrade geometries do not describe stacks per se. but rather a collection of individual detector element positioned as pairs. As the current framework makes no provision for handling such objects a new type of object is required.

Stacked Tracker Geometry classes

  • stackedTrackerDetId
  • stackedTrackerDetUnit
  • stackedTrackerGeometry
  • stackedTrackerGeometryBuilder

The stack objects are stored as a container of detIds (of the stack members) and an associated unique stackedTrackerDetId which encodes the region, layer, iPhi and iZ of the stack.

The stacks are stored as a list of stackedTrackerDetUnits in the stackedTrackerGeometry object, which also provides various helper methods for association ofstackedTrackerDetIds to stackedTrackerDetUnits.

The association of geometric dets (as described by the geometry files of strawman b) into stacks and the creation of the stackedTrackerDetUnits and the stackedTrackerGeometry are performed geometrically (r, phi and z windows) by the stackedTrackerGeometryBuilder.

Stacked Tracker Data Format classes

  • stackedTrackerLocalStub(sim)
  • stackedTrackerLocalStub(digi)
  • stackedTrackerGlobalStub
    • stackedTrackerGlobalStub(sim)
    • stackedTrackerGlobalStub(digi)

Stubs exist in two formats, Local stubs and Global stubs.

Local stubs are associated lists of persistent references to the framework hits (either simhit or digi) within a stack. Local Simhit Stubs are created by the corresponding builder class according to a simple, global geometric cut based on a pT threshold in rphi and a window cut on the projected vertex in z (just like John Jones' work). Local Digi Stubs are created by their corresponding builder class by the DigiMatchingAlgorithm (see below) included through the framework (ie python/config file).

Global stubs are geometric objects with a global position (the average global position of the two constituent hits) and direction (the vector between the two constituent hits). It is intended that this will be extended to include errors on the values to take into account pixel size, etc.

The Global Stubs are currently produced 1-to-1 from the Local Stubs, although there is no a priori reason why this need be the case (ie if you want to cluster).

stackedTrackerDigiMatchingAlgorithm class

The algorithm to match digis between the stack members can have many parameters including r and z position of the stack, separation of the members, rotation of the stack, pitch, etc, and as such will change considerably with each geometry under test. To account for this the DigiMatchingAlgorithm is included from the config/python file as an EventSetupModule.

This allows each user to write their own digi association algorithm for their own geometry.

A shell script included in the scripts directory takes an algorithm name as the single argument and creates a skeleton DigiMatchingAlgorithm for that name.


The tests directory provides several examples of how to use the geometry and data formats.

-- AndrewRose - 09 Dec 2008

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Topic revision: r2 - 2008-12-09 - AndrewRose
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