Sasha, That depends on a compile-time switch. If TRACK_SHOWERS_IN_COLLIMATOR is undefined then tracking of any particle entering the tungsten (primary) collimator or the active collimator volume is abandoned. To do precise beamline background studies, that switch should be enabled. It costs a big factor (15) in run time for background events, so you should be sure you need it before you turn it on. In practice, I find that inside the GlueX solenoid turning if off reduces the rates by no more than 10%, and in places where the rates are high it is much less than that. So for the purposes of getting rate estimates for tracking backgrounds and detector singles rates, it is ok to leave it off. Richard J. ps. It is good to post a general question like this to the mc mailing list. There may be others who would be interested to hear this conversation. Alexander Somov wrote: > Hi Richard, > > A very quick question: > Do you simulate showers in the collimators by default ? > > I found a flag DTRACK_SHOWERS_IN_COLLIMATOR in the > Makefile.orig in HDGeant directory; but it seems that it's > not used (by default). > > Many thanks, > Sascha > > >
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