Difference: LowPtVertices (3 vs. 4)

Revision 42006-11-14 - FerencSikler

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Vertices with low pT tracks

Dijet

Two jet Pythia events (produced with PythiaZ700dijets.cfi). Generated, simulated and reconstructed with CMSSW_1_2_0_pre1 with special code for low pT 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%.

dijet.png

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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 pT reconstruction.

Added:
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Event gallery

EventGallery
 

Vertex resolution

Distribution of vertex residuals with the standard setting (PtMin=1GeV/c) and the low pT setting (PtMin=0).

resolution.png

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

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.
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.
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.
vertices_a.png

Even looser

Increasing ZSeparation to 0.5 cm. A possible cure of the previous problem.
vertices.png

-- FerencSikler - 12 Nov 2006

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