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Overview

The HPS physics reconstruction is implemented primarily by within the HPS Java project .  The EVIO events are first converted into in-memory lcsim events using an implementation of the LCSimEventBuilder interface such as the LCSimEngRunEventBuilder.  These events are accessed using the EventHeader API.  A list of org.lcsim Drivers performs the physics reconstruction by adding additional physics object 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 and clusters.  The driver list is provided by an lcsim xml steering file read in by the lcsim job manager, which parses the XML to create a list of driver objects, calorimeter clusters, reconstructed particles and vertices.  The combined data and recon collections /physics LCIO events are written out to an LCIO files.  Finally, the output is file, which can subsequently be converted to a ROOT DST Data Format for analysis in ROOT.  The LCIO files can events may also be analyzed directly using tools within loaded back into the HPS Java .  

This is the basic recipe for reconstructing HPS data:

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
8. EVIO data files are converted to LCIO events using the EvioToLcio command line utility (if you have an LCIO file you don't need to do this).
9. The HPS Java reconstruction is run to produce physics object collections.
10. The recon LCIO is converted to ROOT DST Data Format so that the events can be easily analyzed in ROOT.
11. DQM files containing plots in ROOT or AIDA format may also be produced from analyzing the reconstruction output.

Oftentimes, the physics reconstruction is performed in the same job (process) as the conversion from raw data to LCIO for efficiency, typically using the EvioToLcio command line utility.

Data Conversion

1.  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 collectionThe EvioToLcio utility converts EVIO to LCIO using an LCSimEventBuilder implementation such as LCSimEngRunEventBuilder.  The generated LCIO events can then be optionally written to disk using an LCIODriver.  The physics reconstruction may also be run in the same process.

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

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

The following collections are added to the event by the ECal reader.

• EcalReadoutHits
• FADCGenericHits
• EcalReadoutExtraDataRelations
• EcalReadoutExtraData 

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default builder will also convert and

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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 fits time vs ADC signal from raw data into fitted hits collection 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 fitted hitsthe strip hits along with the fit results.
3. HelicalTrackHitDriver creates 3D hits (clusters) from clusters of 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  is used to merge the multiple track collections togetherinto a single output collection.
6. The GBLRefitterDriver refits  refits the tracks using GBL and writes a number of additional output collections with this information.
7. TrackDataDriver adds  adds a Generic Object collection  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  Seed Tracker is used for track finding using a set of input tracking strategies.  The  

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

ECal Reconstruction

Reconstructed Particles

Track-cluster matching associates ECal clusters with tracks, and vertex reconstruction is performed.  The matching tracks and clusters are be associated together into a ReconstructedParticle collection.

Package Documentation

.

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

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HPS Java Reconstruction Packages

LCSim Packages

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