ROOT I/O Work for ATLAS at BNL

LAr Detector Description
The identifier for each readout channel from G4 follows the most recent definition from Detector Description Group. However, currently in Athena, the identifier for each channel still follows a old scheme. For EM barrel, the difference is only in the definition of negative/positive region, and the region in middle section at the end of the barrel (The old scheme has only one region for middle section, while the new scheme is more correct, having a different region with deta=0.075 at the end of the barrel). For the time being before we have the new LArID in Athena, I simply convert the new id's into the old id. For sampling=2, and region=1, I put the energy in one cell in the old scheme. For reconstruction, we also need a detector description class.
The current detector description for LAr calorimeter in Athena is LArDetDescrManager, which is a singleton. This will certain involve. Right now, LArDetDescrManager can be built from Zebra event source, or from Objy event source. For events from Root, We would need another source for building LArDetDescrManager. A root representation of the LArDetDescrManager is made, a root file is created for that class. It is simply a TTable with one record for each region. When using RootEventSelector, LArDetDescrManager can be loaded from that Root file (LArDetDescr.root) through the DataBase stream of the same RootSvc.
The root representations of the LAr hits (LArHitContainerRoot) and EventInfo class (EventInfoRoot) are defined in the same package as the converters. The same classes are used by LAr GEANT4 simulation package. All Root files for Athena has to have an object of EventInfo for each event. This contains event number and run number. The Root data classes need to be preprocessed by rootcint, to generate the data dictionary classes. This is done by a script MakeDict in each package. LArCellGaudiRootCnv is an example of converter for Athena DataObjects. It shows how to convert a DataObject in TDS to Root, and how to read in a DataObject from Root persistency. This involves the definition of Root representation of the data object. In this example, it is LArCellContainerRoot.h. A script (MakeDict) in LArCellCnv package should be executed to create the cxx file, LinkIndex.h, and the Dictionary file. The cxx files will then be compiled when gmake is run. We have been using Root version 3.00.06.