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Endcap Shift |
During the installation it was discovered that the ID endcaps (TRT+SCT) needed to be moved out, away from the interaction region by 5mm, to accomindate the ID services.
In M6 the alignment was done wrt tag "ATLAS-CommNF-09-00-00" which did NOT have the endcap shifts in it, because it was based on an earlier tag.
In M6 only endcap A was read out, and thus only A was aligned.
When the switch was made to the ATLAS-GEO- XXXXX tags the endcap
shifts were included in the GEO_Model.
Thus the endcap alignment that was done in M6 (for A only) needed to be changed by 5mm in the
negative Z direction (relative to the previous alignment constants, b/c the endcaps were moved out in the positive Z direction) to be consistent with the ATLAS-GEO tags.
The alignment that was done with the M8 cosmics (both endcaps) was done wrt the ATLAS-GEO-XXXXX tag and thus the shifts did not need to be applied to the endcap alignment constants.
In the end the only alignment constants that were shifted were for endcap A, however the GEO_Model, I was under the impression, had both endcaps moved.
(I did not know there was a relative shift between them however)
-From Grant-
" My understanding was that both were moved out 5mm from there
design position simply because of the extra space used by services in the
region between the barrel and endcap...
The 5mm on both sides was taken into account in the geometry tag (since
ATLAS-CSC-03-00-00).
Also during construction of the endcaps, the positions of the wheels was
different in side A and side C. This was also incorporated in the geometry
tag. That is why side A is different to side C. Those changes were in
since ATLAS-CSC-02-00-00 and in all the commissioning tags.
Most of the information was passed on to us (well to Taeksu and Esben)
from Marc Goulette. Marc was in close contact with the engineers."