Re: BCAL timing from beam test - bafflement - please look

[Alexander Somov <somov@jlab.org>]

Hello Richard,

Thank you for your prompt reply and explanations
(I managed to switch showers on).

But, as far as I understood, you do propagete
photons through the beam line (when showers are switched off);
that also includes sweep magnets ?

(From MCTrajectoryPoint's I see mech=4 for electrons
from the gamma conversion in the sweep magnet regions)

Thanks,
       Sascha






On Tue, 1 Apr 2008, Richard Jones wrote:

> 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
> >
> >
> >
>
>