Fixes to vertex validation

[makortel]

This PR contains the following fixes to vertex validation:

1. Whenever a sim/reco vertex is matched to multiple reco/sim vertices, use the best match as defined by the associator (currently the one with largest number of shared tracks)
   • Old behaviour was to pick the one with smallest event ID
2. Do not reset num_matched_reco_tracks and average_match_quality members of simPrimaryVertex when switching reco vertex collections, since these two do not depend on sim-reco vertex association
3. Fix calculation of z distance to closest vertex (for both reco and sim vertices)

Tested in CMSSW_7_5_X_2015-06-06-2300, following differences in the histograms are expected (examples from 1000 TTbar+25ns PU events; black is old and red is new):

• Small changes in all *MatchedMerged_* histograms (caused by 1.), e.g.
  
• Smal.l changes in all *MultiMatchedGen_* histograms (caused by 1.), e.g.
  
  and therefore in duplicate rates, e.g.
  
• *_SharedTrackFractionSimMatched histograms get filled (caused by 2.), e.g.
  
• Values of *_ClosestDistanceZ decrease (caused by 3.), e.g.
  

@rovere @VinInn

[cmsbuild]

A new Pull Request was created by @makortel (Matti Kortelainen) for CMSSW_7_5_X.

Fixes to vertex validation

It involves the following packages:

Validation/RecoVertex

@cmsbuild, @danduggan, @deguio can you please review it and eventually sign? Thanks.
@GiacomoSguazzoni, @rovere, @VinInn, @appeltel, @cerati, @dgulhan, @venturia this is something you requested to watch as well.
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[deguio]

please test

[deguio]

+1

[cmsbuild]

The tests are being triggered in jenkins.

[cmsbuild]

This pull request is fully signed and it will be integrated in one of the next CMSSW_7_5_X IBs unless changes or unless it breaks tests. This pull request requires discussion in the ORP meeting before it's merged. @davidlange6, @Degano, @smuzaffar

[cmsbuild]

This pull request is fully signed and it will be integrated in one of the next CMSSW_7_5_X IBs unless changes or unless it breaks tests. This pull request requires discussion in the ORP meeting before it's merged. @davidlange6, @Degano, @smuzaffar

[cmsbuild]

Comparison is ready
https://cmssdt.cern.ch/SDT/jenkins-artifacts/pull-request-integration/PR-9519/5402/summary.html

[cmsbuild]

This pull request is fully signed and it will be integrated in one of the next CMSSW_7_5_X IBs unless changes (tests are also fine). This pull request requires discussion in the ORP meeting before it's merged. @davidlange6, @Degano, @smuzaffar

[davidlange6]

+1