5.3.5 Data from calorimeters

In the user common-block ZATRS, the information from the calorimeter(s) is present for each particle seen by any such detector. There might be several calorimeter seeing the same particle; all are included in ZATRS. For particles not seen by the tracking system, the main seen information in the common-block (PVEC, CD, and ABSP) is just a copy of the information for the shower associated to the track (the most energetic one, if there are several). For seen charged particles, the main information is that of the tracking system alone. The rationale for this is that in most cases the tracking-system information has a precision far superior to that of the calorimeters. Be aware, however, that this is not always true. Very high energy particles might be better measured by the calorimeters than the tracking system, since calorimeters get better with energy, tracking detectors worse.

The data of merged showers are in a separate common-block, and even if the routine ZAUSHO is called the shower information in ZATRS is still that of the individual showers. Hence care should be taken if showers are merged : loop only seen charged particles in ZATRS, and neutrals in ZACLU. Further caution is needed in this case, since the showers in ZACLU might be merged by neutrals and charged, and to avoid double-counting the charged contribution should be subtracted of. In real life, it is a hard problem to match tracks with showers, in particular for electrons. However, in the clean conditions of SGV, it is rather easy : there is no brems-strahlung in the detector, and the separation between electromagnetic and hadronic showers is perfect. Therefore, it is suggested to do this subtraction simply by looking at the list CLUORI of contributing showers in each cluster, even though it is to cheat a bit.