LST: Merge T5s After Building

[GNiendorf]

This PR moves the T5-T5 merging kernel from the end of LST to immediately after T5 building, so that downstream duplicate-cleaning and object-building kernels (e.g. pT5 building) can take advantage of the longer tracklet length. The merging kernel is optimized so the timing change is negligible. The three T5 duplicate-cleaning kernels (RemoveDupQuintupletsAfterBuild, RemoveDupQuintupletsBeforeTC, and CrossCleanT5) are also revisited to make use of the new variable track length: longer tracklets are preferred over shorter ones, and pairs of longer tracklets get tighter cuts before being flagged as duplicates. Net effect on PU200 is a significant improvement in displaced-track efficiency with a slight decrease in fake rate and negligible impact on duplicate rate or timing.

See here for more details: Merge_T5.pdf

c.c. @slava77

[cmsbuild]

cms-bot internal usage

[cmsbuild]

+code-checks

Logs: https://cmssdt.cern.ch/SDT/code-checks/cms-sw-PR-51021/49459

• There are other open Pull requests which might conflict with changes you have proposed:
  • File RecoTracker/LSTCore/interface/Common.h modified in PR(s): LST: add LSTGeometry package and associated ESProducer #50679
  • File RecoTracker/LSTCore/src/ModuleMethods.h modified in PR(s): LST: add LSTGeometry package and associated ESProducer #50679
  • File RecoTracker/LSTCore/src/alpaka/Quintuplet.h modified in PR(s): LST: add LSTGeometry package and associated ESProducer #50679

[cmsbuild]

A new Pull Request was created by @GNiendorf for master.

It involves the following packages:

• RecoTracker/LSTCore (reconstruction)

@Moanwar, @cmsbuild, @jfernan2, @mandrenguyen, @srimanob can you please review it and eventually sign? Thanks.
@GiacomoSguazzoni, @VinInn, @VourMa, @dgulhan, @elusian, @felicepantaleo, @gpetruc, @mmasciov, @mmusich, @mtosi, @rovere this is something you requested to watch as well.
@ftenchini, @mandrenguyen, @sextonkennedy you are the release manager for this.

cms-bot commands are listed here

[Moanwar]

test parameters:
enable = hlt_p2_integration, hlt_p2_timing
workflows = ph2_hlt

[Moanwar]

@cmsbuild, please test

[cmsbuild]

-1

Failed Tests: Build
Size: This PR adds an extra 100KB to repository
Summary: https://cmssdt.cern.ch/SDT/jenkins-artifacts/pull-request-integration/PR-5dcb09/53445/summary.html
COMMIT: 1d072cd
CMSSW: CMSSW_17_0_X_2026-05-22-1100/el8_amd64_gcc13
Additional Tests: HLT_P2_INTEGRATION,HLT_P2_TIMING
User test area: For local testing, you can use /cvmfs/cms-ci.cern.ch/week0/cms-sw/cmssw/51021/53445/install.sh to create a dev area with all the needed externals and cmssw changes.

Failed Build

I found compilation warning when building: See details on the summary page.

[GNiendorf]

@Moanwar Compilation warning should be fixed.

[cmsbuild]

+code-checks

Logs: https://cmssdt.cern.ch/SDT/code-checks/cms-sw-PR-51021/49462

• There are other open Pull requests which might conflict with changes you have proposed:
  • File RecoTracker/LSTCore/interface/Common.h modified in PR(s): LST: add LSTGeometry package and associated ESProducer #50679
  • File RecoTracker/LSTCore/src/ModuleMethods.h modified in PR(s): LST: add LSTGeometry package and associated ESProducer #50679
  • File RecoTracker/LSTCore/src/alpaka/Quintuplet.h modified in PR(s): LST: add LSTGeometry package and associated ESProducer #50679

[cmsbuild]

Pull request #51021 was updated. @Moanwar, @cmsbuild, @jfernan2, @mandrenguyen, @srimanob can you please check and sign again.

[Moanwar]

@cmsbuild please test

[Moanwar]

@Moanwar Compilation warning should be fixed.

Thanks!

[cmsbuild]

+1

Size: This PR adds an extra 100KB to repository
Summary: https://cmssdt.cern.ch/SDT/jenkins-artifacts/pull-request-integration/PR-5dcb09/53448/summary.html
COMMIT: de7d518
CMSSW: CMSSW_17_0_X_2026-05-22-1100/el8_amd64_gcc13
Additional Tests: HLT_P2_INTEGRATION,HLT_P2_TIMING
User test area: For local testing, you can use /cvmfs/cms-ci.cern.ch/week0/cms-sw/cmssw/51021/53448/install.sh to create a dev area with all the needed externals and cmssw changes.

HLT P2 Timing: chart

Comparison Summary

Summary:

• You potentially removed 4 lines from the logs
• ROOTFileChecks: Some differences in event products or their sizes found
• Reco comparison results: 10 differences found in the comparisons
• DQMHistoTests: Total files compared: 68
• DQMHistoTests: Total histograms compared: 4830146
• DQMHistoTests: Total failures: 31641
• DQMHistoTests: Total nulls: 0
• DQMHistoTests: Total successes: 4798485
• DQMHistoTests: Total skipped: 20
• DQMHistoTests: Total Missing objects: 0
• DQMHistoSizes: Histogram memory added: 0.0 KiB( 67 files compared)
• Checked 284 log files, 246 edm output root files, 68 DQM output files
• TriggerResults: found differences in 4 / 66 workflows

[GNiendorf]

Failed Build

I found compilation warning when building: See details on the summary page.

I think this previous issue is a false positive from -Wstringop-overflow/-Warray-bounds by the way. The reported sizes don't match the actual StdArray types. I used a local-reference workaround to silence it, pulling the row refs out of the loop, not sure if this particular compilation check should just be disabled if it is buggy?