
 Consider also the active silicon layer, of the extra part 
 of the detector, as sensitive. 
 Define a "tracker-like" hit type for such sensitive layer,
 that is, create one hit (for event) only the first time
 some energy is deposited in such layer: then, add to it
 any other energy deposit which happens in the same event.
 To do, you need three things:

 --- HIT CLASS : write an Hit class, with only the deposited
     energy information.

 --- SENSITIVE DETECTOR : write a Sensitive Detector class which,
     in the  ProcessHits  method, creates a different Hit each time 
     a particle deposit some energy.

 --- DETECTOR : the above sensitive detector must be associated
     to the active silicon layer of the first part of the detector.


 NB) Physically, you could imagine the silicon layer 
     as a matrix of pixels detectors, without "gaps" in between.







