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Overview

The HPS physics reconstruction algorithm is implemented in by the HPS Java code project, which uses org.lcsim extensively for basic utilities like event processing, detector description and conditions interfaces.  

The track reconstruction first converts the raw ADC vs time signals 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 collection for each unique tracking strategy used in the finding step.

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 of the GBL algorithm.  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 A set of lcsim Drivers is used to process the raw data collections and produce collections of Tracks, Clusters, and ReconstructedParticles.  The 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  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

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.

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