Standard Analyzer Algorithm¶

9 March 2007

The "standard analyzer" provides a generic event loop and analysis chain that will (hopefully) be sufficient for many nuclear physics analysis tasks. The event loop and high-level algorithm are implemented in the method THaAnalyzer::Process() of the class THaAnalyzer. The standard spectrometer processing algorithm is implemented in the method THaSpectrometer::Reconstruct() of the class THaSpectrometer.

THaAnalyzer::Process( THaRunBase& run ) carries out the following functions:

• Open the CODA input file associated with the run using THaRun::Open().
• Open the ROOT output file if not already open. If the file is already open, but the filename has changed, close the old file and open a new one.
• Loop over all events in the CODA file.
• Skip events until the a prestart event is found. Extract the time stamp of the prestart event and call Init(time_stamp) for every THaApparatus object defined in the gHaApps list and every THaPhysicsModule object defined in the gHaPhysics list.
• After initializing the modules (and thus setting up their global variables), load the tests defined in the definition file (set with SetCutFile()).
• After loading the tests, load the output definitions (THaOutput::Init()) from the output definition file (set with SetOdefFile()). This sets up a TTree in the output file.
• After finding the prestart event and initializing the apparatuses, analyze events in the event range of the run. For physics events, do
  • For each apparatus defined in gHaApps, call THaApparatus::Decode().
  • For each apparatus, call CoarseReconstruct(). If the apparatus does not implement CoarseReconstruct(), this call does nothing.
  • For each apparatus, call Reconstruct().
  • For each defined physics module, call Process().
  • Fill the output tree and histograms by calling THaOutput::Process().
• For scaler events, do
  • For each THaScaler object defined in gHaScalers, call THaScaler::LoadData().
• Close() the CODA input file.
• Write() the ROOT output file.

If an apparatus is a THaSpectrometer, processing in the Reconstruct() stage is carried out by THaSpectrometer::Reconstruct() as follows:

• Loop over all THaTrackingDetectors and call their CoarseTrack() methods.
• Loop over all THaNonTrackingDetectors and call their CoarseProcess() methods.
• Loop over all THaTrackingDetectors and call their FineTrack() methods.
• Loop over all THaNonTrackingDetectors and call their FineProcess() methods.
• Call TrackCalc(). This method usually calculates overall track properties such as the absolute momentum and beta and may also be used to identify the "Golden Track".
• Call FindVertices(). This method usually reconstructs tracks to the target.

TrackCalc() and FindVertices() have to be implemented by the actual spectrometer class (see how to write an apparatus class).