LowPtVertices < CMS

CMS Web>LowPtVertices (2006-11-14, FerencSikler) (raw view)

---+!!Vertices with low p<sub>T</sub> tracks

%TOC%

---++Dijet

Two jet Pythia events (produced with !PythiaZ700dijets.cfi). Generated, simulated and reconstructed with CMSSW_1_2_0_pre1 with special code for low p<sub>T</sub> reconstruction. The distribution of number of found vertices (!NVertices) with several !NTrkMin settings, keeping ZSeparation=0.05cm and !PtMin=0. While with !NTrkMin=5 there are a lot of events with multiple vertices, with !NTrkMin=10 their frequency is below 1%.

%ATTACHURL%/dijet.png

---+++Event gallery
EventGalleryDijet

---++Minimum bias

Minimum bias Pythia p+p events at 14 !TeV. Generated, simulated and reconstructed with CMSSW_1_2_0_pre1 with special code for low p<sub>T</sub> reconstruction.

---+++Event gallery
EventGallery

---+++Vertex resolution
Distribution of vertex residuals with the standard setting (!PtMin=1GeV/c) and the low p<sub>T</sub> setting (!PtMin=0). %BR%

%ATTACHURL%/resolution.png

The resolution has strong multiplicity dependence, shown here as function reconstructed track multiplicity !NRecTracks. %BR%

%ATTACHURL%/multidep.png

---+++Multiple vertices

Distribution of the number of reconstructed (charged pixel) tracks for several NVertices values is shown, that is for different number of found vertices. The following four plots are done with different vertex reconstruction parameters in !RecoPixelVertexing/PixelVertexFinding/data/PixelVertexes.cff (!ZSeparation, !NTrkMin, !PtMin).

---++++Standard parameters
      Only high multiplicity events give vertex. %BR%
      %ATTACHURL%/vertices_c.png

---++++Lowering !PtMin to 0
      Now all tracks take part in vertex finding. Even low multiplicity events give a vertex, if, say, !NRecTracks > 8. %BR%
      %ATTACHURL%/vertices_b.png

---++++Even looser
      Lowering !NTrkMin to 2. This choice gives vertex to very low multiplicity events, but at the same time many events will have multiple vertices. %BR%
      %ATTACHURL%/vertices_a.png

---++++Even looser
      Increasing !ZSeparation to 0.5 cm. A possible cure of the previous problem. %BR%
      %ATTACHURL%/vertices.png

-- Main.FerencSikler - 12 Nov 2006

Topic revision: r4 - 2006-11-14 - FerencSikler

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