Page History

...

Although these are not flagged, the ACDGAPDIST and ACDPOCA plots show minor differences for the background test.
All of these are quantities that are sensitive to changes in the ACD geometry.

This change affects side tiles and so the vertical tests are not very sensitive to it.

Also, the trapezoids (r36) are bigger than the squares (r37). You can see that in general and as expected there are more entries (hits) in the ACD plots for r36.

Eric C. took a look at the system test recon files for these releases. The plot below shows the difference in the edge of edges for tile 110 for v15r37 (black) vs v15r36 (red).

Here is what Eric found for the number of hits coming close to tracks for each release from r33 to r39 (trapezoids are in r35 and r36):

The trapezoids (r36) are bigger than the squares (r37). You can see there are more POCA hits for r35 and r36, part of this should be the size difference. As you might guess this also means there are more entries (hits) in general in the ACD system test plots for r35 and r36.

The effect on the ribbons was not obvious, but Joanne adds:

Just one small footnote - the ribbon geometry is slightly different since the ribbons follow the tiles; see schematics at http://www.slac.stanford.edu/exp/glast/ground/LATSoft/geometry/pictures/ACD/newSides/XRibbonAnnot.png (older geometry)
and http://www.slac.stanford.edu/exp/glast/ground/LATSoft/geometry/pictures/ACD/newerSides/v1r45p2-Xmeas-print.png

I asked about the y offset between the square and trapezoid and Joanne responds that the new positions should be more accurate. These come from the CAD model, while the older positions were based on approximations.

Eric also notes that the difference in nPOCA between r38 and r39 is curious. The only differences are G4Propagator and AnalysisNtuple. The G4Propagotor work relates to stuck tracks. See the GR v15r39 report. This has apparently had some effect on details of the event simulation.