Physics Reconstruction Documentation

Overview

The reconstruction is implemented within the HPS Java project as a chain of org.lcsim Drivers (event processors) described by lcsim xml and run by the lcsim job manager.  The EvioToLcio command line tool is used to convert the EVIO to LCIO events using an LCSimEventBuilder such as LCSimEngRunEventBuilder.  The LCIO events are accessed in Java code through the EventHeader API.  The Drivers add output collections to the event such as tracks, calorimeter clusters, reconstructed particles and vertices.  The combined data/physics LCIO events are written out to an LCIO file, which can subsequently be converted to ROOT DST Data Format.  The LCIO events may also be loaded back into the HPS Java environment for analysis.

Basic Steps

These are the steps performed in reconstructing the data:

1. EvioToLcio command line tool is run with command line parameters like the EVIO file(s) and the path to the XML steering file.
2. The JobControlManager loads the steering file which defines the chain of reconstruction Drivers and their parameters.
3. Detector Conditions including per channel calibrations are read and applied in Driver detectorChanged methods.
4. Each EvioEvent is read with EvioReader and converted to an LCIO raw data event using an appropriate LCSimEventBuilder.
5. The HPS Java reconstruction runs on the LCIO event, adding additional reconstruction collections to the events.
6. The events are written to an LCIO file containing the results of the recon.
7. The output LCIO file is converted to ROOT DST Data Format for analysis.

Steps 1-6 are typically performed in the same job using the EvioToLcio command line utility.

User analysis can be performed on the LCIO files using the job manager command line tool or within the ROOT environment using the DSTs.

Reconstruction Drivers 

The reconstruction Driver chain is defined in production steering files such as EngineeringRun2015FullRecon.lcsim, which are kept in this SVN folder and typically accessed as a class resource from a jar file.

Data Collections

Algorithm Details

Data Conversion

The LCSimEventBuilder defines an interface for converting from EVIO to LCIO events, with the LCSimEngRunEventBuilder providing the current implementation of this conversion process.  EVIO collections are processed by a reader which gets raw bank data and converts it into a typed LCIO collection.

SVT data banks are handled by an SvtEvioReader and converted into RawTrackerHit and GenericObject collections.

Various modes of EVIO ECal data are converted using the EcalEvioReader.

The default builder will also convert and write DAQ config information, EPICS data, and scaler bank data into the output LCSim events, if these banks are present in the EVIO data.

Track Reconstruction

These are the primary steps involved in the HPS Java track reconstruction:

1. RawTrackerHitFitterDriver is used to fit the ADC vs time signals from the raw data and writes a new collection with the fit result.
2. DataTrackerHitDriver creates stereo hit pairs from the strip hits along with the fit results.
3. HelicalTrackHitDriver creates 3D hits (clusters) from input stereo hits.
4. TrackerReconDriver runs track finding on the 3D hit collection.
   1. Track finding runs multiple times with different tracking strategy files, creating a track collection for each strategy used.
5. The MergeTrackCollections Driver is used to merge the multiple track collections into a single output collection.
6. The GBLRefitterDriver refits the tracks using GBL and writes a number of additional output collections with this information.
7. TrackDataDriver adds a Generic Object collection containing additional information about the track for persistency.

The tracking packages in lcsim form the basis for HPS's tracking algorithms through usage and extension.  Seed Tracker is used for track finding using a set of input tracking strategies.  

The track fit from lcsim is further refined using a Java implementation (port) of the GBL C++ algorithm.

Each track has a TrackType assigned which indicates the SeedTracker algorithm used, in a bitwise fashion, and sets bit 6 (2^5=32) if the track was refined by GBL. The TrackType is inherited by any particle and is obtained with the getType() method. See: TrackType and StrategyType for details.

Additional References

This paper describes the LCIO track parameters.

These slides provide some details about how tracking strategies are used (see pages 4 & 8).

Cluster Reconstruction

These are the basic steps of the ECal reconstruction:

1. EcalRawConverterDriver converts RawTrackerHit input collection into CalorimeterHit collection using the EcalRawConverter.
2. ReconClusterDriver uses the ReconClusterer to create calorimeter Cluster collection from input hits collection.
3. CopyClusterCollectionDriver copies the clusters (with raw energies) to a different collection.

The copied collection will be updated with corrected energies in the step which creates recon particles.

Additional References

This CLAS Note describes the basic clustering algorithm.

This HPS Note covers position corrections and other analysis.

Reconstructed Particles

The ReconParticleDriver creates ReconstructedParticle objects representing the final state particles from the event reconstruction.  These are tracks with matching clusters (when applicable).  It also performs vertex reconstruction and creates a number of candidate particle collections.

The ReconParticleDriver is sub-classed by the actual HpsReconParticleDriver from the steering which adds Møller candidate collections.

Java Packages

HPS Java Reconstruction Packages

The HPS Java Documentation can be used to browse the packages and classes used for physics reconstruction.

LCSim Packages

These lcsim packages are used extensively within the HPS Java reconstruction code.