Vertices with low p_T tracks

Vertices with low pT tracks Minimum bias Pythia p+p events at 14 TeV . Generated, simulated and reconstructed with CMSSW_1_2_0_pre1.

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

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

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.

* Lowering PtMin to 0: Now all tracks take part in vertex finding. Even low multiplicity events give a vertex, if, say, NRecTracks > 8.

* 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.

* Even looser: Increasing ZSeparation to 0.5 cm. A possible cure of the previous problem.

-- FerencSikler - 12 Nov 2006