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Re: Problem with PndVertexFitter for particles with neutral charge [message #18289 is a reply to message #18279] Fri, 29 May 2015 14:27 Go to previous message
Ralf Kliemt is currently offline  Ralf Kliemt
Messages: 507
Registered: May 2007
Location: GSI, Darmstadt
first-grade participant

From: *

The vertex fitters (PndKinVtxFitter/PndKalmanVtxFitter) operate on a minimum of two charged tracks. For anything else you may use PndVtxPoca, which analytically calculates the vertex. From the top of my head:
PndVtxPoca pocafinder;
for (int j=0; j<lambda0.GetLength(); ++j)
  PndKinVtxFitter vertexfitterLambda0 (lambda0[j]);
  RhoCandidate * lambda0Fit = lambda0[j]->GetFit();
  for (int j=0; j<antiLambda0.GetLength(); ++j)
    PndKinVtxFitter vertexfitterAntiLambda0 (antiLambda0[j]);
    RhoCandidate * antiLambda0Fit = antiLambda0[j]->GetFit();
    TVector3 pbarpvertex;
    crossCheck.Combine(lambda0Fit, antiLambda0Fit);

    double doca = pocafinderGetPocaVtx(pbarpvertex,crossCheck);
    // now you have a vertex written to pbarpvertex and a measure of the distances between the trajectories (i.e. a quality criterium)

If you have charged(!) particles combining to crossCheck, you may want to update the four-momentum along the helix to the vertex via the analysis:
bool check = theAnalysis->PropagateToPoint(crossCheck, pbarpvertex);

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