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The HPS physics reconstruction is implemented in the HPS Java project as a series chain of org.lcsim Drivers.  The drivers and their parameters and execution order are described  operating on lcsim events that are accessed using the EventHeader API.  The driver list is described in an lcsim xml steering file which configures the lcsim job manager.  A driver is simply an event processing component that operates on each event in a record processing loop.  For example, a driver might convert ADC data to a hit class or perform track finding.  

Before the drivers can process the data, it must be converted from the EVIO Data Format written by the DAQ.  The   The EvioToLcio command line tool reads the EVIO data events using EvioEvents using an EvioReader and these are converted into LCIO events by an LCSimEventBuilder such as LCSimEngRunEventBuilder.  These collections have types such as RawTrackerHit.  With the data now in a compatible format for lcsim, the driver chain from the lcsim job manager is run on the event  The driver chain is then run to add additional physics object collections to the EventHeaderthe event.  The events with the data and recon collections are written out to LCIO files.  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. 

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