ACTSTracking

Package for running track reconstructions using the ACTS library. This is not tied to a given geometry, but has been developed for the Muon Collider detector model v1.

ACTSTracking is distributed under the GPLv3 License.

License and Copyright

Copyright (C), ACTSTracking Authors

ACTSTracking is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version.

This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details.

You should have received a copy of the GNU General Public License long with this program. If not, see http://www.gnu.org/licenses/.

Resource Files

The ACTSTracking package contains several resource files (tracking geometry, material description). Their path is given to processors via configuration parameters (ie TGeoFile). If the path is relative, then the following locations are search for it:

• current working directory
• ACTSTRACKING_SOURCEDIR = ${CMAKE_SOURCE_DIR}, aka source code location
• ACTSTRACKING_DATADIR = ${CMAKE_INSTALL_FULL_DATADIR}/ACTSTracking}, aka result of make install

Available Processors

See examples/ for steering files demonstrating the usage of the provided processors.

ACTSProcBase

Base processor implementing some of the common actions. This processor is not to be used directly. It is designed to be inherited by other processors that implement the specific track reconstruction algorithm

The responsibilities include:

• Load tracking detector geometry and material.
• Create magnetic field description.

Parameter	Description
MatFile	Path to the material description json file. Can be empty.
TGeoFile	Path to the tracker geometry file.

Tracking Geometry

The tracking geometry is loaded from a TGeoManager stored inside a ROOT file at parameter TGeoFile. The building of the ACTS volumes is done using the ACTS TGeo plugin. The builder parameters are currently hardcoded for the MuColl_v1 detector model.

Material is optionally loaded using by specifying the MatFile parameter. It should corresponds to the JSON file generated using the ACTS material mapping tools.

Files corresponding to the MuColl_v1 detector model are available inside data/.

Magnetic Field

A constant magnetic field is assumed. The strength is taken from the loaded DD4hep detector description.

ACTSTruthTrackingProc

Processor that implements truth tracking. Pseudo-tracks are formed by finding hits associated to a charged MC particles. The pseudo-tracks are then fit using a Kalman Filter. This processor is equivalent to TruthTrackFinder.

Parameter	Description
TrackerHitCollectionNames	Name of the TrackerHit input collections
SimTrackerHitRelCollectionNames	Name of TrackerHit to SimTrackerHit relation collections
MCParticleCollectionName	Name of the MCParticle input collection
TrackCollectionName	Name of track output collection

ACTSTruthCKFTrackingProc

Processor that implements truth-seeded Combinatorial Kalman Filter. Seeds for the CKF algorithm are formed by using the kinematics of charged MC particles, with vertex set at (0,0,0).

Input/Output Configuration

Parameter	Description
TrackerHitCollectionNames	Name of the TrackerHit input collections.
MCParticleCollectionName	Name of the MCParticle input collection (used for seeding).
TrackCollectionName	Name of track output collection.

CKF Configuration

Parameter	Description
CKF_Chi2CutOff	Maximum local chi2 contribution.
CKF_NumMeasurementsCutOff	Maximum number of associated measurements on a single surface.

ACTSSeededCKFTrackingProc

Processor that implements tripled seeding Combinatorial Kalman Filter. This processor can be used for track reconstruction without any truth assumptions.

Input/Output Configuration

Parameter	Description
TrackerHitCollectionNames	Name of the TrackerHit input collections.
SeedCollectionName	Name of seed output collection.
TrackCollectionName	Name of track output collection.

Triplet Seeding Configuration

Parameter	Description
SeedingLayers	Layers to use for seeding in format VolID LayID, one per line. ID's are ACTS GeometryID's. * can be used to wildcard.
SeedFinding_RMax	Maximum radius of hits to consider.
SeedFinding_DeltaRMin	Minimum dR between hits in a seed.
SeedFinding_DeltaRMax	Maximum dR between hits in a seed.
SeedFinding_CollisionRegion	Size of the collision region in one direction (assumed symmetric).
SeedFinding_ZMax	Maximum z of hits hits to consider.
SeedFinding_RadLengthPerSeed	Average radiation length per seed.
SeedFinding_SigmaScattering	Number of sigmas to allow in scattering angle.
SeedFinding_MinPt	Minimum pT of tracks to seed.

CKF Configuration

Parameter	Description
RunCKF	Run tracking using CKF. False means stop at the seeding stage.
PropagateBackward	Run CKF outside-in.
InitialTrackError_RelP	Track error estimate, momentum component (relative).
InitialTrackError_Phi	Track error estimate, phi (radians).
InitialTrackError_Lambda	Track error estimate, lambda (radians).
InitialTrackError_Pos	Track error estimate, local position (mm).
CKF_Chi2CutOff	Maximum local chi2 contribution.
CKF_NumMeasurementsCutOff	Maximum number of associated measurements on a single surface.

ACTSDuplicateRemoval

Processors to remove overlapping (sharing multiple hits) tracks. The algorithms works as follows:

1. Sort input tracks by tan(lambda).
2. Create final tracks container
3. Compare each sorted input track against last 10 final tracks
   1. Skip tracks not sharing more than 50% of hits. Shared fractions are defined as shared hits / min(track 1 hits, track 2 hits)
   2. Replace final track if input track is of higher quality. Higher quality tracks has more hits. In case of same number of hits, the higher quality track has a smaller chi2.