Overview of the clustering algorithm

All cuts  mentioned below are set online by configuration files and offline by ZGANA datacards and therefore can be changed easily. Clustering in the FCAL beampipe regions is disabled because of timing reasons.

Layer1 (40 transputer modules: per region):

• Do the scanning through all the Hac cells with energy > HacCellCut (110 MeV). Add to global sums. Check if this cell is a neighbour of a cell hit. If so, add the cell to the cluster belonging to that cell. Check for overflow  (MAX.LAYER1.CLUSTERS=  10) and  if so stop combining.
• Do an energy cut on the hac preclusters:E>HacPreclusterCut (200 MeV).
• Do the scanning through all the Emc cells: E>EmcCellCut (60 MeV). Check if this cell is a neighbour of a cell hit an add the cell to the cluster belonging to that cell.   If so, add the cell to the cluster belonging to that cell. Check for overflow  (MAX.LAYER1.CLUSTERS=  10) per region and  if so stop combining.
• Do an energy cut on the emc preclusters:E>EmcPreclusterCut (100 MeV).
• Combining: take a hac precluster and then loop over all emc preclusters.  Calculate energy weighted mean. Classify clusters according  to  efr=EMC/(EMC+HAC). If EMC clusters (efr>75%) distance from mean < 22 cm, for hadron clusters   <33 cm for combining. Total energy cut on  EMC clusters: EmShowerCut  (400 MeV) and for hadron clusters: JetCut (1 GeV). Selection of muons  not enabled.
• Calculate FCal Beampipe energysums

Layer2 (6 transputer modules: combining regions):

• Calculate energy  and timing sums
• Loop over clusters in own region and neighbouring regions.  Calculate energy weighted mean. Cut on cluster and classify according to efr=EMC/(EMC+HAC) . If EMC clusters (efr>75%) distance from mean < 22 cm, for hadron clusters <33 cm for combining. Total energy cut on EMC clusters: EmShowerCut  (500 MeV) and for hadron clusters: JetCut (2.5  GeV).
• Check for overflow  (MAX.LAYER2.CLUSTERS=  10) per region and  if so stop combining.
• Translate cluster coordinates into global coordinates (rsphere*phi*sin(theta), rsphere*theta), where rsphere=65.

Layer3 (1 transputer module: overall CAL):

1. Calculate energy and timing sums
2. Loop over clusters in  neighbouring regions. Calculate energy weighted mean. Cut on cluster and classify according to  efr=EMC/(EMC+HAC). If EMC clusters (efr>75%)distance from mean < 7, for hadron clusters <10  in the special coordinates for combining. Total energy cut on clusters: for EMC clusters EmShowerCut  (500 MeV) and for hadron clusters JetCut (2.5  GeV).
3. Translate in ZEUS spherical coordinates (theta,phi)

A description of the variables  (more or less up to date) is given in a note. All variables can set in ZGANA by data cards. N.B. the output variables concerning radii of clusters have no meaning.