TrigVertexFitter Package

This package contains implementations of various vertex fitting tools for the LVL2 reconstruction.

Author

Dmitr.nosp@m.y.Em.nosp@m.eliya.nosp@m.nov@.nosp@m.cern..nosp@m.ch

Introduction

The package defines and implements the following class:

• TrigL2Vertex - an extended TrigVertex class, contains a full covariance matrix of vertex and tracks. Note that the maximum number of tracks is limited to 9 so that the maximum size of the covariance is 30x30.

The package provides an abstract interface:

• ITrigVertexingTool - an auxiliary tool to be used in vertex fitting tools and applications in order to facilitate operations with TrigL2Vertex instances (e.g. TrigL2Vertex -> TrigVertex conversion, adding tracks to a vertex, setting constraints, etc.)

The list of vertex fitting tools is below:

• TrigVertexFitter this a first prototype of the LVL2 vertex fitter based on ITrigVertexFitter abstract interface. Note that this tool will become obsolete soon as it will be replaced by TrigL2VertexFitter
• TrigL2VertexFitter - an improved and extended fitter with capability of mass-constrained fitting. It uses TrigL2Vertex class as input/output
• TrigVertexingTool - a toolbox to facilitate handling of TrigL2Vertex class

How to use LVL2 vertexing tools:

• Example I : fitting Ds(phi pi) vertex with phi(KK)

StatusCode sc = toolSvc()->retrieveTool("TrigL2VertexFitter","TrigL2VertexFitter",m_L2vertFitter);
if ( sc.isFailure() ) {
    log << MSG::FATAL << "Unable to locate TrigL2VertexFitter tool " << endmsg;
    return sc;
}
 
sc = toolSvc()->retrieveTool("TrigVertexingTool","TrigVertexingTool",m_vertexingTool);
if ( sc.isFailure() ) {
    log << MSG::FATAL << "Unable to locate TrigVertexingTool tool " << endmsg;
    return sc;
} 
 
 
// creating empty TrigL2Vertex
 
TrigL2Vertex* pL2Ds=new TrigL2Vertex();
 
// adding TrigInDetTrack* to the vertex 
 
m_vertexingTool->addTrack((*track1),pL2Ds,Trk::kaon);
m_vertexingTool->addTrack((*track2),pL2Ds,Trk::kaon);
m_vertexingTool->addTrack((*track3),pL2Ds,Trk::pion);
 
// note that particle masses are attributed in accordance with Trk::kaon, Trk::pion, etc. 
 
// vertex fit
 
StatusCode sc=m_L2vertFitter->fit(pL2Ds);
              
if(sc.isSuccess()) {
    //invariant mass calculation
    sc=m_vertexingTool->calculateInvariantMass(pL2Ds);
    if(sc.isSuccess()) {
        // estimation of Ds meson perigee parameters 
        sc=m_vertexingTool->createMotherParticle(pL2Ds);
        if(sc.isSuccess()) {
           log<<MSG::DEBUG<<"Ds created:"<<endmsg;
       log << MSG::DEBUG << "Ds particle parameters"<<endmsg;
       log << MSG::DEBUG << "d0="<<pL2Ds->m_getMotherTrack()->a0()<<
                      "  z0="<<pL2Ds->m_getMotherTrack()->z0()<<
                  "  phi0="<<pL2Ds->m_getMotherTrack()->phi0()<<
                  "  eta="<<pL2Ds->m_getMotherTrack()->eta()<<
                  "  pT="<<pL2Ds->m_getMotherTrack()->pT()<<endmsg;
           // now we can create TrigVertex ("simplified" vertex) from fitted 
           // TrigL2Vertex
           TrigVertex* p_DsV=m_vertexingTool->createTrigVertex(pL2Ds);
       if(p_DsV!=NULL){
 
                                log << MSG::DEBUG << "Ds vertex Fit: x= y= z=" << p_DsV->x() << " " << p_DsV->y() << " " << p_DsV->z() << endmsg;
                                log << MSG::DEBUG << "Ds mass = " << p_DsV->mass() << endmsg;
                                double chi2prob=1.0-Genfun::CumulativeChiSquare(p_DsV->ndof())(p_DsV->chi2());
                                log << MSG::DEBUG << "Chi2 probability of the Ds fit = " << chi2prob << endmsg;
          }
    }
    }
}
delete pL2Ds;

• Example II : Fitting vertex with a mass constraint: Ds -> phi(KK) + pi, where a mass constraint (with phi mass) is imposed on KK pair

double PHIMASS = 1020.0;
 
TrigL2Vertex* pL2V=new TrigL2Vertex();
 
m_vertexingTool->addTrack((*track1),pL2V,Trk::kaon);
m_vertexingTool->addTrack((*track2),pL2V,Trk::kaon);
m_vertexingTool->addTrack((*track3),pL2V,Trk::pion);
 
// setting up the constraint
 
m_vertexingTool->setMassConstraint(pL2V,(*track1),(*track2),PHIMASS);
 
// mass constrained fit
 
StatusCode sc=m_L2vertFitter->fitWithConstraints(pL2V);