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Basic Recipe

This is the basic recipe for reconstructing HPS data:

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
6.  EVIO data files are read in and converted to LCIO events.
7. The HPS Java reconstruction is run to add physics object collections to the events.
8. The events are written to an LCIO file containing the results of the recon.
9. The recon output LCIO file can be is converted to ROOT DST Data Format for analysis.

Oftentimes, steps Steps 1-3 6 are typically performed in the same job (process) for efficiency using the EvioToLcio command line utility.

Overview

The HPS physics reconstruction is implemented in the HPS Java project as a chain of org.lcsim Drivers which process LCIO Data Format events that are accessed using the EventHeader API.  The driver list is described in an lcsim xml steering file which is configured by the lcsim job manager.  

The EVIO Data Format is converted into LCIO by an LCSimEventBuilder such as LCSimEngRunEventBuilder.  The EvioToLcio command line tool reads EvioEvents with an EvioReader and then uses an event builder to create LCIO events representing the raw data.  The driver chain is then run to perform the physics reconstruction which will add additional object collections to the event.  The combined events with the data and recon collections are written out to an LCIO file.  The LCIO output can be converted to ROOT DST Data Format for ROOT compatibility, or it may be loaded back into HPS Java for analysis. 

Steering Files

The production recon steering files such as EngineeringRun2015FullRecon.lcsim are kept in this SVN folder and typically accessed as a class resource from a jar file by the job manager. 

Depending on the tool being used, steering files may also be accessed as XML files on disk.

Data Conversion

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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  and GenericObject collections collections.

Various modes of EVIO ECal data 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,

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and scaler bank data

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 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 converts SVT raw data into fitted hits collection by fitting ADC vs time signals 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 fitted strip hits along with the fit results.
3. HelicalTrackHitDriver creates 3D hits (clusters) from input stereo hits.
4. TrackerReconDriver runs  runs track finding on the 3D hit collection.
   1. Track finding is run 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 into 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.

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

The copied collection will be updated with corrected energies in the next 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  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 Moller candidate Møller candidate collections.

Data Collections

Java Packages

HPS Java Reconstruction

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Packages

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

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LCSim Packages

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