Alignment of the TRT Endcaps with 1 DoF
After the new L2 endcap scheme was implemented and validated, the L2 alignment was run on cosmic data from 2008.
Runs including the TGC trigger were used to enhance the number of endcap tracks.
The alignment was done using combined SCT + TRT tracks, and rotations around global Z were aligned.
The alignment converged and improved Endcap Tracking. Systematic misalignments of the 4-plane carbon rings were seen inside the 8-plane wheels.
This systematic misalignment was seen in both the A and B wheels endcaps and for both Endcap A and C.
From talking to the experts, its clear that the misalignments are consistent with flaws in table used to machine the wheels. See the presentation here for details.
Alignment of the TRT Endcaps with 3 DoF
After the L2 alignment of rotations was performed it was decided to align the L2 Endcaps with 3 DoF, rotations about global-Z, and translations about X and Y.
The alignment was preformed similar that described above and also convered with improvemtns in the endcap tracking.
The systematic misalignment of the 4-plane endcap rings within the 8-plane wheel was agian observed, as well as a "L1-like" misalignment of the B wheels with respect to the A wheels. See the presentation here for details.