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The HPS physics reconstruction is implemented primarily by the HPS Java project.  The EVIO events from raw data 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 This initial conversion translates the EVIO data banks into a set of object collections in the event with types such as RawTrackerHit.  A list of org.lcsim Drivers performs  then performs the physics reconstruction by adding processing these raw data collections to create additional physics object collections to the event such as tracks and clustersin the EventHeader.  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 now combined data and recon collections in each event are written to out 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.  

Basic Recipe

This is the basic recipe for reconstructing HPS data:

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.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.

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