The Tertiary Tracks Vertex Finder

Complete: 3

Overview

The TertiaryTracksVertexFinder (TTVF) is designed for reconstructing secondary vertices in jets. It is documented in CMS Note 2006/027 where its implementation in the previous software framework ORCA is called TertiaryVertexTrackFinder (TVTF). Some information about the CMSSW implementation can be found in this talk

The basic idea is to find tracks from a tertiary charm hadron decay in the b-c decay cascade, and associate them to the secondary vertex. The procedure is as follows: First, the standard TrimmedKalmanVertexFinder is run in order to reconstruct secondary vertex candidates. Then, a filter is run on the vertices in which primary vertices, conversions, nuclear interactions or K0 candidates are rejected. The b-flightline is reconstructed from the primary and secondary vertex. Tracks close to the b-flight line not associated to a vertex are searched and added to the secondary vertex. Note that the position of the secondary vertex is not recalculated after the additional tracks have been added.

The fitter is implemented in the package RecoVertex/TertiaryTracksVertexFinder

Usage

TertiaryTracksVertexFinder fitter;
vector<TransientVertex> vertices = fitter.vertex(vector<TransientTrack> tracks, TransientVertex pv);

The first argument is the set of tracks from which secondary vertices are to be found. Usually those will be tracks associated to a jet (e.g. using the JetTracksAssociator).

The second argument is the primary vertex of the event, converted to a TransientVertex.

The TransientTracks which are needed for the vertex fitter, are built using the TransientTrackBuilder in exactly the same way as for regular tracks.

Parameters

The parameters are the following, and are set via the appropriate set methods:

Parameter Name Description Default method
minPt The pT cut to apply to the tracks 0. setPtCut
trackCompatibilityCut probability below which a track is considered incompatible with the 1st vertex candidate formed 0.05 setTrackCompatibilityCut
trackCompatibilityToSV probability below which a track is considered incompatible with the next vertex candidates formed 0.01 setTrackCompatibilityToSV
vertexFitProbabilityCut probability below which a vertex is rejected 0.01 setVertexFitProbabilityCut
maxNbOfVertices maximum number of vertices searched for (0 means all vertices which can be found) 0 setMaxNbOfVertices

#Review Status

Review Status

Editor/Review and date Comments
FrankPeterSchilling - 04 Apr 2007 Page author
JennyWilliams - 10 Apr 2007 edited for swguide inclusion
ThomasSpeer - 27 Feb 2009 Review and update

Responsible: ThomasSpeer
Last reviewed by:

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Topic revision: r3 - 2009-02-27 - ThomasSpeer



 
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