[BeamSpot] fit 1D projections of PV distribution to get initial values for 3D fit parameters

[rmanzoni]

back porting #10780

[slava77]

@rmanzoni please clarify on the importance of the fix for the current data taking.
If it's not very important, it will be integrated after 25ns startup is over.

[cmsbuild]

A new Pull Request was created by @rmanzoni (Riccardo Manzoni) for CMSSW_7_4_X.

[BeamSpot] fit 1D projections of PV distribution to get initial values for 3D fit parameters

It involves the following packages:

RecoVertex/BeamSpotProducer

@diguida, @cvuosalo, @cerminar, @cmsbuild, @slava77, @mmusich can you please review it and eventually sign? Thanks.
@makortel, @GiacomoSguazzoni, @rovere, @VinInn, @cerati, @dgulhan this is something you requested to watch as well.
You can sign-off by replying to this message having '+1' in the first line of your reply.
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@Degano you are the release manager for this.
You can merge this pull request by typing 'merge' in the first line of your comment.

[rmanzoni]

Hi @slava77,

the beam spot fit failures affect the beam spot determination run in the prompt calibration loop. If the failure rate gets large enough, typically when the actual beam spot position is vary far off the a priori position hard coded in the module, the impact on prompt calibration could be substantial.

Two examples:

1. https://hypernews.cern.ch/HyperNews/CMS/get/beamspot/135.html about 20% of the fits failed because of this reason
2. https://hypernews.cern.ch/HyperNews/CMS/get/beamspot/137.html a particularly nasty situation occurred at LS124, where the fit converged to a secondary minimum and the resulting BS Z position was -8. cm with a tiny error, so tiny that when (weighted) averaged out over the full run set the Z to be around -6. cm, while for the rest of the run it was correctly estimated to be around -1.3 cm

[slava77]

Riccardo, thank you for the explanation.
It sounds like the short answer is "we want it included as soon as possible"
@davidlange6

[sushilchauhan]

These changes will also be important for online beamspot because we also see similar fit failure issue as mentioned by Ricardo here. I already check in a previous collision run and it worked fine.

[cvuosalo]

@cmsbuild please test

[cmsbuild]

The tests are being triggered in jenkins.

[diguida]

@slava77 we agree with your executive summary.

[cmsbuild]

-1
Tested at: 49541a6
When I ran the RelVals I found an error in the following worklfows:
1001.0 step1

DAS Error

you can see the results of the tests here:
https://cmssdt.cern.ch/SDT/jenkins-artifacts/pull-request-integration/PR-10782/7327/summary.html

The following merge commits were also included on top of IB + this PR after doing git cms-merge-topic:
49541a6
You can see more details here:
https://cmssdt.cern.ch/SDT/jenkins-artifacts/pull-request-integration/PR-10782/7327/git-log-recent-commits
https://cmssdt.cern.ch/SDT/jenkins-artifacts/pull-request-integration/PR-10782/7327/git-merge-result

[cvuosalo]

@cmsbuild please test
Try again, hoping for no more DAS errors

[cmsbuild]

The tests are being triggered in jenkins.

[cmsbuild]

+1
Tested at: 49541a6
https://cmssdt.cern.ch/SDT/jenkins-artifacts/pull-request-integration/PR-10782/7336/summary.html

The following merge commits were also included on top of IB + this PR after doing git cms-merge-topic:
49541a6
You can see more details here:
https://cmssdt.cern.ch/SDT/jenkins-artifacts/pull-request-integration/PR-10782/7336/git-log-recent-commits
https://cmssdt.cern.ch/SDT/jenkins-artifacts/pull-request-integration/PR-10782/7336/git-merge-result

[cmsbuild]

Comparison is ready
https://cmssdt.cern.ch/SDT/jenkins-artifacts/pull-request-integration/PR-10782/7336/summary.html

[diguida]

+1
for 49541a6
The correspondent version in 76X #10780 has already been approved by AlCa.

Comparison with baseline, wf 25202.0

[cvuosalo]

+1

For #10782 49541a6

Changing the initial values of the primary vertex fit. The 75X and 76X versions of this PR, #10781 and #10780, have already been approved by Reco.

The code changes are satisfactory. Jenkins tests against baseline CMSSW_7_4_X_2015-08-14-1100 show very small changes in PV fit results, but none of these differences are significant. See above and #10780 for example plots of the small changes in the fit results.

[cmsbuild]

This pull request is fully signed and it will be integrated in one of the next CMSSW_7_4_X IBs once checked with relvals in the development release cycle of CMSSW (tests are also fine). This pull request requires discussion in the ORP meeting before it's merged. @davidlange6, @Degano, @smuzaffar

[davidlange6]

+1