Hello Jeremy,

The HPS Ecal flange was produced by taking measurements on the 3D drawings we received from the French engineers. These are the same drawings that I think were used to create the tesselated version of the vacuum chamber. The information was converted directly into GEANT4 primitive shapes. The GDML file was then created my GEANT4, which allows a geometry to be saved directly into a GDML file. I have seen some problems when such a file is subsequently rendered using the ROOT gdml reader. I don't know if the error is in ROOT (I suspect it is), or in GEANT4. The errors I have encountered had to do with the trapezoid shapes.

Of the problems you mention, I only agree with #1, the back flange was left out to save some time. Since this is away from the beam, I did not think it would create much if any back splash. We can take some more time and add this flange if it seems needed. If we are concerned about back splash and additional sources of noise, I would rather take some time and implement the vacuum chamber around the silicon trackers, which gets hit by degraded electrons and is a direct source of background.

2) I do not see what you mean with the additional top plate. We followed the engineering drawing faithfully. Could you please specify what is missing?

3) As the rendering from GEANT4 shows, there is no gap between the photon tube and the plate it sits along side. I think this is an artifact of the viewer you are using.

4) We extensively tested for overlap with GEANT4, which has specialized ray tracing routines build in to look for geometry errors. We did not find a single problem with this geometry. It is possible that the viewer you are using does not properly take into account the boolean actions taken on the volumes.

5) I do not see the problems that you mention when I render the volumes in GEANT4, see below.


No sign of a gap with GEANT4 rendering:

I don't see a problem on the electron side either:

On Feb 1, 2013, at 12:38 AM, "McCormick, Jeremy I." <[log in to unmask]> wrote:


Along with Sho, I was looking at the "new" HPS ECal flange model that was created by one of Maurik's students, and it seems there are a number of problems with it that we've identified:

1) The back plate is missing.
2) There is an additional top plate that is also missing.  (Sho has more info on this.)
3) There is a small gap between the photon tube and the plate it sits alongside, at the back of the flange.
4) The connector between the photon and electron tubes seems to have an overlap with the electron box.
5) The angles between the electron box, which has some angle to it that increases in the beam direction, do not seem to exactly match those of some of the components that sit alongside it, which could explain some of these other issues.

This could be hard to understand in description, so I've attached some files, including two screenshots and the VRML file I used to take them.

I used the Deep View VRML viewer to look at the file.

Sho has looked in detail at the GDML file, but we're not sure exactly how to go about fixing it in order to make it match the CAD or "as built" version.  Any suggestions would be welcome.  I'm not sure either of us has the necessary time to do this right now.

I would actually like to get more information from Maurik on how this file was generated, as the GDML does not look hand-generated.  Was there some kind of script used?  If so, would it be possible to get a copy?

My feeling is that #1 and #2 could have an impact on the simulation, as extra dead material could lead to increased showering and backsplash into the calorimeter.  The other minor geometric errors are not likely to have as much effect, though overlaps should be avoided as they can lead to strange and sometimes wrong behavior in the Geant4 tracking  engine when the geometry is simulated.

Let me know if you have any questions or comments.

And please make sure to keep hps-software in the reply list so everyone can participate in this discussion.  Thanks.


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