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The HPS physics reconstruction algorithm is implemented primarily by the HPS Java code project, which uses org.lcsim extensively for basic utilities like event processing, detector description and conditions interfaces.   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 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.  The combined data and recon collections are written to LCIO files.  Finally, the output is converted to a ROOT DST Data Format for analysis in ROOT.  The LCIO files can also be analyzed directly using tools within HPS Java.  

Quick Steps

1. 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).
2. The HPS Java reconstruction is run to produce physics object collections.
3. The recon LCIO is converted to ROOT DST Data Format so that the events can be easily analyzed in ROOT.
4. 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.

Track Reconstruction

The track reconstruction first converts the raw ADC vs time signals data into SVT strip hits, which are then clustered together into stereo hits.  A collection of 3D hits is created from these stereo hits.  Track finding and fitting is performed using the input 3D hit collection.  The tracking creates a number of collections containing Track objects.  There will be a track , with one collection for each unique tracking strategy used in the track finding step. The  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. 

1. RawTrackerHitFitterDriver fits raw time vs ADC signal into fitted hits collection.
2. DataTrackerHitDrivercreates 2D stereo hits from strip hits.

Reconstructed Particles

Track.  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.

A list of lcsim Drivers is used to process raw data collections and produce collections of physics objects that are accessed through the EventHeader API.  A driver list is defined in an lcsim xml steering file read in by the lcsim job manager.  The drivers created by the manager are processed using the LCSimLoop, which is a sequential recording processing loop.  The job manager can read in lists of LCIO files as defined in the XML steering format or from command line options.  Post-processing or analysis of the recon can be done by reading in the LCIO files and supplying a steering file which implements the user's algorithm.

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.

Quick Steps

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 collection.

Package Documentation

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

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