Re: CDC phase shifts

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

Dave, Beni,
> 1. Richard: Why are these placed with each straw in the first place?
They are not placed in each straw, they are placed in each straw 
sector.  Because the straws have to stick through the endplate and 
displace the material there, the endplate has to be cut up into little 
pieces and stuck on the end of each straw.  Think of a shisk-kabob.

Technically this creates a volume overlap conflict in Geant3, but since 
I know how the tracking works I know what I can get away with.  This is 
an efficient way to do an effective boolean subtraction in G3.  It is 
not rigorously correct, but it works correctly for all but a small 
fraction of tracks -- ones that enter the endplate outside a hole but 
then penetrate into a hole on the way through.  These guys do not see 
the holes, and see endplate material all the way through, but they are a 
small fraction of the tracks.

Richard Jones


David Lawrence wrote:
>
> Hi Beni,
>
>    I am finally sitting down to take a look at this again and I have a 
> question. When I look in the CentralDC_HDDS.xml file you sent me, I 
> see a discrepancy I don't understand. In the option-1 section of the 
> file, the placement of the "CDPU" and "CDPD" volumes seems to have 
> been dropped from the "DS" volumes. For example:
>
> Repository version:
>  <composition name="CDCsector_1_option-1" envelope="DS1">
>    <posXYZ volume="CDCstrawShort" X_Y_Z="10.96 0.0 0.0" />
>    <posXYZ volume="CDPU" X_Y_Z="0.0 0.0 -75.45" />
>    <posXYZ volume="CDPD" X_Y_Z="0.0 0.0 +75.20" />
>  </composition>
>
> Beni Custom Version:
>  <composition name="CDCsector_1_option-1" envelope="DS1">
>    <posXYZ volume="CDCstrawShort" X_Y_Z="0.0 0.0 0.0" />
>  </composition>
>
>
> The "CDPU" and "CDPD" volumes define the upstream and downstream end 
> plates. These ARE placed n the "centralDC_option-1" volume in both 
> versions which seems like the appropriate place. So, I guess my 
> questions are:
>
> 1. Richard: Why are these placed with each straw in the first place?
> 2. Beni: Why did you remove them from the option-1 geometry in the 
> file you sent me?
>
> Regards,
> -David