[10_6] Backport Pythia fix for alphaS running

[mseidel42]

Activate backported fixes for alphaS running cms-externals/pythia8#30

[cmsbuild]

A new Pull Request was created by @mseidel42 (Markus Seidel) for branch IB/CMSSW_10_6_X/gcc700.

@cmsbuild, @smuzaffar, @aandvalenzuela, @iarspider can you please review it and eventually sign? Thanks.
@perrotta, @dpiparo, @rappoccio you are the release manager for this.
cms-bot commands are listed here

[rappoccio]

hold

• Hold this until decision comes from PPD to approve this backport.

[cmsbuild]

Pull request has been put on hold by @rappoccio
They need to issue an unhold command to remove the hold state or L1 can unhold it for all

[jordan-martins]

Hi,

This feature had a validation to assess the impact, right? If so, can the studies be shared? In any case, I would propose some official validation to be delivered by PdmV based on GEN-related people (please open a JIRA ticket in the PDMVRELVALS project).

Thanks,
Jordan
FYI @cms-sw/ppd-l2 @mseidel42 @cms-sw/generators-l2 @sihyunjeon @agrohsjean

[sihyunjeon]

@agrohsje

[mseidel42]

Hi Jordan,

The impact on some ttbar observables was shown in the GEN meeting on Monday: https://indico.cern.ch/event/1293969/contributions/5438463/attachments/2668515/4624955/GEN%20Meeting%20190623%20v2.pdf#page=16

We think that this fix is the crucial change between Pythia 8.307 and 8.309 shown there.
By lucky coincidence, the impact is not large for our default alphaS value of 0.118.

However, we agreed to leave the defaults at the old (buggy) behavior and added new Pythia options to activate the bugfix for special samples requested by experts.
So I would not expect any change in the RelVals unless I managed to hide some more bugs in the code...

Best,
Markus

[sihyunjeon]

@mseidel42 i think @jordan-martins / ppd just wants to doubly make sure that pythia option switches you added functions as it is designed, just in case to avoid surprises. gen might comment more

[menglu21]

Hi @jordan-martins, I think @mseidel42 already explained well the motivation of this backport, and the validation using ttbar in https://indico.cern.ch/event/1293969/contributions/5438463/attachments/2668515/4624955/GEN%20Meeting%20190623%20v2.pdf#page=16 shows expected results from the fix. Since some UL requests i.e., bb4l may need this new feature (the correct results rather than the coincident-"correct" result) and I think it's worth to have it in the 10_6, or you want some more validation on other processes

[agrohsje]

we did such campaigns in the past via an extended relval. wouldn't;t that make sense to make sure we didn't miss anything. not that I don't trust markus. just to be 100% certain.

[Saptaparna]

please test

[cmsbuild]

-1

Summary: https://cmssdt.cern.ch/SDT/jenkins-artifacts/pull-request-integration/PR-f9d279/33546/summary.html
COMMIT: 9506bf4
CMSSW: CMSSW_10_6_X_2023-07-02-0000/slc7_amd64_gcc700
User test area: For local testing, you can use /cvmfs/cms-ci.cern.ch/week0/cms-sw/cmsdist/8555/33546/install.sh to create a dev area with all the needed externals and cmssw changes.

External Build

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

[smuzaffar]

@cms-sw/generators-l2 , we need cms-externals/pythia8#30 to be signed/megred first and then we can start testing this PR (as this PR will need changes e.g. correct commit of cms-externals/pythia8 after the merge of cms-externals/pythia8#30)

[smuzaffar]

please test

[cmsbuild]

Pull request #8555 was updated.

[smuzaffar]

hold

• Hold this until decision comes from PPD to approve this backport.

@rappoccio , should we unhold this PR now?

[cmsbuild]

+1

Summary: https://cmssdt.cern.ch/SDT/jenkins-artifacts/pull-request-integration/PR-f9d279/34897/summary.html
COMMIT: bf6f949
CMSSW: CMSSW_10_6_X_2023-09-24-0000/slc7_amd64_gcc700
User test area: For local testing, you can use /cvmfs/cms-ci.cern.ch/week0/cms-sw/cmsdist/8555/34897/install.sh to create a dev area with all the needed externals and cmssw changes.

Comparison Summary

Summary:

• You potentially removed 5 lines from the logs
• Reco comparison results: 4 differences found in the comparisons
• DQMHistoTests: Total files compared: 35
• DQMHistoTests: Total histograms compared: 3215686
• DQMHistoTests: Total failures: 2
• DQMHistoTests: Total nulls: 0
• DQMHistoTests: Total successes: 3215350
• DQMHistoTests: Total skipped: 334
• DQMHistoTests: Total Missing objects: 0
• DQMHistoSizes: Histogram memory added: 0.0 KiB( 34 files compared)
• Checked 144 log files, 103 edm output root files, 35 DQM output files
• TriggerResults: no differences found

[smuzaffar]

+externals

@rappoccio @antoniovilela , feel free to unhold and merge it for next 10.6.X Ibs/releases

[mseidel42]

Just noticed that this is still open

[mseidel42]

@rappoccio ?

[menglu21]

@rappoccio , could we unhold this PR

[menglu21]

@rappoccio a kind ping

[rappoccio]

unhold

[rappoccio]

+1

[cmsbuild]

This pull request is fully signed and it will be integrated in one of the next IB/CMSSW_10_6_X/gcc700 IBs (tests are also fine). This pull request will now be reviewed by the release team before it's merged. @rappoccio, @sextonkennedy, @antoniovilela (and backports should be raised in the release meeting by the corresponding L2)

[rappoccio]

merge