Re: too many cdcTruthHits

[Richard Jones <richard.t.jones@uconn.edu>]

Beni,

This is an example of boundary-crossing chatter that sometimes happens 
in geant3.  For a detailed explanation of why it happens, ask me 
sometimes.  The main thing is that it was understood by the authors, and 
accepted as a consequence of having a small tracking error epsilon, 
compared with the scale of the experiment.  Our experimental scale is 
10m, and our epsil is 10 microns, a span of 1e6.  Rounding errors in 
single-precision can be on this same order, especially when non-trivial 
rotations are involved, as in the CDC stereo layers.  There is nothing 
wrong with these.  It is just that the tracking takes an extra 
micro-step in trying to get from one side of a boundary to the other.

I agree that it is undesirable that extra truth points be generated by 
this tracking chatter.  I will circulate a fix later today that will 
eliminate extra truth points caused by this effect.  When you see it 
checked in, please run a test and confirm that the problem is resolved.

Richard Jones

Beni Zihlmann wrote:
> Hi Richard,
>
> Mark found that quite often he sees more cdcTruthHis than CDC layers.
> While I was looking into this I found some weired behavior I do not
> quite understand. Maybe you know  immediately whats going on.
> So I every time hdgeant gets into GUSTEP.F I print out the following
> line:
> GUSTEP: "volume name" x , y , z
> Then I call savehits.F regardless of it is sensitive volume or not. In 
> savehits.F
> the variable INWVOL is checked and if it is ==1 (enter new volume) I 
> print
> the following line:
> Enter volume: "volume name" x, y, z
> and if it is ==2 (leaving volume) I print
> Leaving volume: "volume name" x, y, z
>
>
> So I get the following output I do not understand:
>
> ....
> GUSTEP: CDCO  -12.68686       55.57017       149.4882   Leaving 
> volume: CDCO  -12.68686       55.57017       149.4882      3.4471179E-09
> GUSTEP: LASS  -12.68686       55.57017       149.4882   Enter volume: 
> LASS  -12.68686       55.57017       149.4882      3.4471179E-09
> GUSTEP: LASS  -13.48804       56.87979       151.7202   GUSTEP: LASS  
> -14.31226       58.17541       153.9520   GUSTEP: LASS  
> -15.15931       59.45658       156.1835   GUSTEP: LASS  
> -16.02898       60.72287       158.4149   GUSTEP: LASS  
> -16.92102       61.97383       160.6460   GUSTEP: LASS  
> -17.39989       62.62656       161.8214   Leaving volume: LASS  
> -17.39989       62.62656       161.8214      3.9509893E-09
> GUSTEP: LASS  -17.39989       62.62656       161.8214   Enter volume: 
> LASS  -17.39989       62.62656       161.8214      3.9509893E-09
> GUSTEP: LASS  -17.40071       62.62768       161.8234   Leaving 
> volume: LASS  -17.40071       62.62768       161.8234      3.9510719E-09
> GUSTEP: BM01  -17.40071       62.62768       161.8234   Enter volume: 
> BM01  -17.40071       62.62768       161.8234      3.9510719E-09
> GUSTEP: BM01  -18.67320       64.34534       164.9268   Leaving 
> volume: BM01  -18.67320       64.34534       164.9268      4.0778918E-09
> GUSTEP: BM02  -18.67320       64.34534       164.9268   Enter volume: 
> BM02  -18.67320       64.34534       164.9268      4.0778918E-09
> GUSTEP: BM02  -19.94047       66.05596       168.0175   Leaving 
> volume: BM02  -19.94047       66.05596       168.0175      4.2041912E-09
> GUSTEP: BM03  -19.94047       66.05596       168.0175   .....
>
> The problem is that hdgeant leave the volume LASS and enters it again 
> right away.
> From the coordinates I gather that this happens close to the border of 
> the volume.
> Do you have any explanation why this happens? This happens also quite 
> frequent
> in the CDC straws where Mark found it in the firs place causing 
> multiple cdcTruthHits.
>
> cheers,
> Beni
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