BEMC data is always available using standard StEvent collections.  This is true regardless of whether one is analyzing simulations or real data, or whether the actual input file is in a geant.root,  event.root, or mudst.root format.  The appropriate BEMC maker (StEmcADCtoEMaker for real data, StEmcSimulatorMaker for simulations) will create an StEvent in-memory if necessary and fill the BEMC collections wth the correct data.

Three different types of calorimeter objects are available:

StEmcRawHit -- a hit for a single detector element (tower, smd strip, or preshower channel)

StEmcCluster -- a cluster is formed from a collection of hits for a single BEMC subdetector (tower / smd-eta / smd-phi / preshower)

StEmcPoint -- a point combines StEmcClusters from the different subdetectors.  Typically the SMD clusters are used to determine the position of points, and in the case of e.g. pi0 decay photons they also determine the fraction of the tower cluster energy assigned to each photon.  The absolute energy scale is set by the tower cluster energy.  Current point-making algorithms do not use the preshower information.

For more information see the StEvent manual.