7.4.1 Offline Primary Vertex Finding

Complete: 4
Detailed Review status

Contents

Algorithm description

The offline primary vertex finder algorithm is documented in CMS Note 2006/029, section 3.1. In short, it proceeds as follows:

  • the reconstructed tracks are clustered into several primary vertex candidates, according to the z-coordinate of the point of closest approach of the tracks to the z-axis
  • each primary vertex candidate is cleaned up from incompatible (secondary) tracks
  • primary vertex candidates compatible with the beam line are retained.

Instructions for CMSSW_1_2_0_pre9

Production of primary vertices

Offline primary vertices can be reconstructed from RS or CKF tracks. Two different modules, OfflinePrimaryVerticesFromRSTracks and OfflinePrimaryVerticesFromCTFTracks are thus provided. The corresponding default config files can be found in cvs in

RecoVertex/PrimaryVertexProducer/data/OfflinePrimaryVerticesFromRSTracks.cfi, RecoVertex/PrimaryVertexProducer/data/OfflinePrimaryVerticesFromCTFTracks.cfi.
The sequences vertexreco (for CTF trakcs) and vertexreco_rs (for RS tracks) are defined in RecoVertex/Configuration/data/RecoVertex.cff and putting either one in the path decides about the type of tracks to be used.

The example below shows how to reconstruct primary vertices from a file containing tracks, and store these vertices in a file called pv_reco.root. The module sequence is defined in the following CMSSW config file demoProducePrimaryVertex.cfg. The tracks used on input are also copied, for analysis and debugging.

scramv1 project CMSSW CMSSW_1_2_0_pre9
cd CMSSW_1_2_0_pre9/src
project CMSSW
cvs co -r V00-01-10 Validation/RecoVertex
cd Validation/RecoVertex
scramv1 b
cd test
eval `scramv1 runtime -csh`
cmsRun demoProducePrimaryVertex.cfg

This produces pv_reco.root. To see it:

root -l pv_reco.root
TBrowser a;

This brings up the ROOT browser. Click on ROOT Files and on pv_reco.root to access the event data. Click on Events. The data collections retained, tracks and vertices, now appear. Clicking further, you may have a quick look at the distributions of the x, y, z, chi-squared, degrees of freedom of the reconstructed vertices

To exit ROOT, enter:
.q

Vertex reconstruction analysis

In cmsRun mode, the primary vertices can be analyzed with the PrimaryVertexAnalyzer module by running demoAnalyzePrimaryVertex.cfg:

cmsRun demoAnalyzePrimaryVertex.cfg

in the same directory. A root histogram file simpleVertexAnalyzer.root is produced, that, in addition to histograms of the fitted position, covariance, chi2 and degrees of freedom, also contains results of sanity checks of the number of valid track links and invalid fit parameters.

root simpleVertexAnalyzer.root
pullx->Draw()
eff->Draw()
nans->Draw()

A simple test of the input track parameters is done by

cmsRun demoAnalyzeTracks.cfg

which produces histograms of track parameter pulls. For instance, to look at curvature and z0:

root simpleTrackAnalyzer.root
pull0->Draw()
pull4->Draw()

Review status

Reviewer/Editor and Date (copy from screen) Comments
Main.werdmann - 04 Dec 2006 update

Responsible: ThomasSpeer
Last reviewed by: Werdmann - 04 Dec 2006

Topic attachments
I Attachment History Action Size Date Who Comment
Unknown file formatcff OfflinePrimaryVerticesFromCTFTracks.cff r1 manage 0.2 K 2006-07-19 - 10:58 UnknownUser .cff for vertices from CTF tks
Texttxt OfflinePrimaryVerticesFromCTFTracks_cff.txt r1 manage 0.2 K 2006-07-27 - 22:32 AnneHeavey .cff for vertices from CTF tks
Unknown file formatcff OfflinePrimaryVerticesFromRSTracks.cff r1 manage 0.2 K 2006-07-19 - 10:57 UnknownUser .cff for vertices from RS tks
Texttxt OfflinePrimaryVerticesFromRSTracks.cff.txt r1 manage 0.2 K 2006-07-27 - 22:31 AnneHeavey .cff for vertices from RS tks
Texttxt analyzePrimaryVertex_cfg.txt r1 manage 0.4 K 2006-07-28 - 17:44 AnneHeavey  
Texttxt analyzeTracks_cfg.txt r1 manage 0.4 K 2006-07-28 - 17:46 AnneHeavey  
Texttxt demoAnalyzePrimaryVertex.cfg.txt r1 manage 0.8 K 2006-11-17 - 12:05 UnknownUser  
Texttxt demoProducePrimaryVertex.cfg.txt r1 manage 1.2 K 2006-11-17 - 11:25 UnknownUser  
JPEGjpg dx.jpg r1 manage 17.3 K 2006-06-07 - 16:59 VanlaerPascal  
JPEGjpg dz.jpg r1 manage 16.8 K 2006-06-07 - 16:56 VanlaerPascal  
JPEGjpg ndf.jpg r1 manage 16.1 K 2006-06-07 - 17:01 VanlaerPascal  
Unknown file formatcfg producePV.cfg r1 manage 0.6 K 2006-07-19 - 09:50 UnknownUser .cfg file for offline p.v. production from already produced tracks
Texttxt producePV_cfg.txt r1 manage 0.6 K 2006-07-27 - 22:29 AnneHeavey .cfg file for offline p.v. production from already produced tracks
C source code filec pv.C r1 manage 0.4 K 2006-06-16 - 18:29 VanlaerPascal  
C source code filec pv080.C r1 manage 0.6 K 2006-07-10 - 14:39 UnknownUser pv inspection in FWLITE, cmssw 080_pre3
C source code filec pv111.C r2 r1 manage 0.4 K 2006-11-15 - 12:21 UnknownUser  
GIFgif pvx.gif r2 r1 manage 7.8 K 2006-07-18 - 10:00 UnknownUser x-residuals, cmssw_080_pre5
GIFgif pvz.gif r2 r1 manage 8.0 K 2006-07-18 - 10:01 UnknownUser z-residuals, cmssw_080_pre5
C source code filec tracks.C r1 manage 0.5 K 2006-06-07 - 14:18 VanlaerPascal  
C source code filec tracks080.C r1 manage 0.8 K 2006-07-10 - 14:18 UnknownUser track inspect in FWLITE, cmssw080_pre3
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Topic revision: r38 - 2008-02-04 - CMSUserSupport


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