Optimisations for FastTrackFinder running as an offline algorithm for ITk

Merged Elliot Watton requested to merge ewatton/athena:ewatton-OptimiseITkFTF into master

This MR introduces two small changes which improve the performance of FTF when running as an offline algorithm via the use of the flags.Tracking.useITkFTF flag. This MR only impacts upgrade code, and additionally does not impact the performance of running FTF with the trigger for ITk (only as offline algorithm).

The two changes refer to increasing the pTmin cut on triplets in the FTF seeding step via increasing the Triplet_MinPtFrac parameter. The second change refers to reducing the z width of the TrigRoiDescriptor created down to +/- 150mm to match that of offline for ITk. Both of these changes result in an increased efficiency in the region -1.5 < eta < 1.5 of up to 4%, and a significant decrease in FTF's total time per event of around 200ms (approximately 50ms in the seeding step and 150ms in the combinatorial track fitting step). This was tested on a Run 4 ttbar + 200 pileup RDO.

This MR is only for upgrade, so targetting master.

This work relates to EFTRACK-142

Tagging @baines @demelian

Edited by Elliot Watton

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