7.3 Vertex Reconstruction
Complete:
Detailed Review status
Goals of this page:
This tutorial describes:
- the pixel standalone reconstruction of tracks and primary vertices (for HLT),
- the fitting of tracks to a common vertex,
- the offline primary vertex reconstruction that uses tracks reconstructed from both pixel and silicon strip hits.
Contents
Introduction
Vertex reconstruction usually involves 2 steps, vertex finding and vertex fitting. Vertex finding involves grouping tracks into vertex candidates. The vertex-finding algorithms can be
very different depending on the physics case (primary or secondary vertex finding, reconstruction of exclusive decays, etc.). Vertex fitting involves determining the best estimate of
the vertex parameters (position, covariance matrix, and track parameters constrained by the vertex position and their covariances) for a given set of tracks, as well as indicators of the fit quality (total chi2, number of degrees of freedom, or track weights).
Pixel standalone track and vertex reconstruction is fast enough to be used at HLT. Fitting a single vertex from reconstructed tracks is a common step in the reconstruction of high-level physics objects such as tau's and B's.
Offline primary vertex reconstruction yields ultimate vertex position resolution as well as the best possible
estimation of the primary vertex position error matrix.
Set up your Environment
Set your runtime environment (shown for release %WBRELEASENEW%):
cd CMSSW_%WBRELEASENEW%/src
cmsenv
Data samples
For this tutorial, any data sample reconstructed with the standard sequence can be used, as long as it countains tracks and primary vertices. These are available in both the RECo and AOD samples.
Typically the user wishes to analyze an already generated and reconstructed sample, such as PhysicsValidation or in CMS.ReleaseValidation samples. To find out these samples, please refer to the WorkBook
Locating Data Samples section.
In some cases the user may want to analyze reconstructed Tracks in a private production sample: some examples of configuration files to generate data samples can be found in
SWGuideTrackRecoSequences (particle gun muons and H->ZZ->4mu).
Individual Tutorial Sections
Several other topics are described in the
Vertex Reconstruction section of the SWGuide:
Information Sources
CMS Note 2006/026, "Track reconstruction, primary vertex finding and seed generation with the Pixel Detector", S.Succiarelli et al.
CMS Note 2006/032, "Vertex Fitting in the CMS Tracker", T.Speer et al.
CMS Note 2006/029, "Impact of CMS Silicon Tracker Misalignment on Track and Vertex Reconstruction", P. Vanlaer et al.
Review status
Responsible: Thomas Speer