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MuonCombined - Restrict number of ID candidates for inside -> out chain

Johannes Junggeburth requested to merge jojungge/athena:Restrict_InDetExtension into master

Hi everybody,

this is another tuning of the inside -> out reconstruction chain to reduce the CPU footprint. The MuonInDetToMuonSystemExtensionAlg selects only tracks where hits are found in the corresponding MS sector. ID tracks with no hope of combining them to a MuGirl track are then not extrapolated through the entire MS - ideally. With increasing pile-up it becomes quite likely that we have in every sector of the MS few background hits such that the rejection power of this mechanism is essentially zero.

Segment-making itself has a huge rejection power against background hits. The changes introduced in this MR exploit segment information to seed the ID tracks for the inside -> out chain:

  * The segment must not be used by MuidCo
  * The segment must pass the minimum quality defined by the SegmentSelectionTool
  * The calo-extension & the segment must seperated by delta Theta < 0.2
  * The segment must be in the same sector as the calo extension

These requirements are essentially copy-pasted from the MuonSegmentTagTool. It's found that an application of these alone would reduce the CPU foot-print of the most this alg by roughly 50%. However, this essentially kills cases where MuGirl can successfully recover segments due to the usage of the ID track parameters at the muon station and we must somehow stick to the though seeds. The Hough seeds are cleaned from all hits used in any selected muon segment. Seeds with at least 4 hits in a muon chamber are selected. An ID track is then considered as candidate if it is separated in dEta by 0.1 from a seed in the same sector.

To assess the gain in CPU, I performed a SPOT test on 1k events of data17. Below the total CPU in times in milliseconds of the affected algorithms are posted

Algorithm master patched
MuonInDetToMuonSystemExtensionAlg 123575 87799
MuonInDetToMuonSystemExtensionAlg (LRT) 53387 39024
MuonInsideOutRecoAlg 58543 50163
MuGirlAlg (LRT) 15431 12849
MuonSegmentTagAlg 4057 3801
MuonSegmentTagAlg (LRT) 1825 1755
Overall 256818 195391

Overall the CPU is reduced by roughly 25%. The impact on the reconstruction performance is evaluated using 250k single-muons and found to be negligible All_quick_plots.pdf

Edited by Johannes Junggeburth

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