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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 configures is configured by the lcsim job manager.  A driver is simply an event processing component that operates on each event in a record processing loop and may add new object collections to the event.  For example, a driver might convert ADC data to a hit object hits collection or it could perform track finding and create new track object collections.  

Before the drivers can process the data, it must be is converted from the EVIO Data Format written by the DAQ by an LCSimEventBuilder such as LCSimEngRunEventBuilder.  The EvioToLcio command line tool reads EvioEvents using  with an EvioReader and these are converted into LCIO events by an LCSimEventBuilder such as LCSimEngRunEventBuilderthen uses the event builder on them 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. 

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