d0root version v9.0

• Change Log
• Instructions
• Links
• Known Problems

Change Log

Structure

Vertexing

• Add beam spot information for primary vertex search.

  A new D0BeamSpot class has been introduced. It was designed to be used with the beam spot database of the cvs package beamspotoffline, but can be used with any other format. If the beam spot is available, the 1-pass primary vertex finder can take this information into account for track selection.

  Here is an example of use:

  D0BeamSpot* beam = new D0BeamSpot; beam->Set(z_x_slope, z_y_slope, z_x_intercept, z_y_intercept); pvFinder->SetBeamSpot(beam);

  where pvFinder is the 1-pass VertexGlobalFinder class.

  The beam object should be created only once, whereas it has to be "set" for every run from the beam spot database.

  *** Primary vertex resolution improves from 38 micros to 33 microns by using beam spot information.***. Please seeAriel's talk for more details

• Add track chi2 quality cuts for primary vertex search.

  A new parameter was added in the primary vertex constructor (for both 1 and 2 pass algorithms) to cut on track chi2.

  Here is an example of use:

  PrimaryVertexGlobalFinder2Pass* pvFinder = new PrimaryVertexGlobalFinder2Pass(0.5, //min track pT 0.5, //max transverse dca [cm] 3.0, //dca significance cut (2nd pass) 2.0, //deltaZ (z-track-clustering) 2, //min number of SMT hits 10. //max vertex \chi^{2} pdof. 10. //max track \chi^{2} pdof. );

• Constraint kinematic fitting tools.

  A new general VertexConstraint algorithm for Kinematic fitting was introduced. It implements a constraint fit minimization using the Lagrange multiplier technique. Users can implement different kinematic vertex constraints by just specifying the constraint equation.

  Two concrete implementations are provided:

  VertexBeamConstraint

  After a primary vertex is found, VertexBeamConstraint constraints the x and y vertex position according to the following equation:

   
    g(x) = x - beam(x) = 0
    g(y) = y - beam(y) = 0
  

  where beam(x) and beam(y) are assumed to have a given width.

  Here is an example of use:

  VertexBeamConstraint bConstraint; double beamParameters[3] = { 9.82003e-04, // beam_x 4.83037e-02, // beam_y 0.0030 // beam_sigma(xy) bConstraint.Constraint(PV, beamParameters); D0Vertex* constrainedVertex = bConstraint.GetConstrainedVertex();

  where PV is the original primary vertex (a D0Vertex object)

  VertexMassConstraint

  Modifies the vertex position, track momentum, and track-vertex and track-track correlations according to the equation:

   g(x) = E^2 - P^2 - M^2 = 0
  

  where

  E = sum_j{ sqrt(m^2 - p_j^2) }
  P = sum_j{p_j}
  

  and m is the track mass, p the track momentum.

  Here is an example of use:

  VertexMassConstraint jpsiConstraint; double jpsiMass[1] = { 3.09688}; jpsiConstraint.Constraint(vtx, jpsiMass); D0Vertex* constrainedVertex = jpsiConstraint.GetConstrainedVertex();

Instructions (TMBTree)

In order to run the script, you first need to create a new release area:

//Create release area
//----------------------------------

kinit

newrel -t p14.05.01 mydir
cd mydir
d0setwa
source Maked0root_v9.0.csh

Run analysis code

from mydir directory:
root runBphysicsAnalysis_TMBtree.C

This command will create an instance of the class BphysicsAnalysis called "b". To see the list of available methods please look at d0root_btag/analysis/BphysicsAnalysis.h

To create a B-rtuple with information about J/Psi, Phi and B vertices, do:

    b->Process_diMuons("myOutputFileName", all_muons, muon_pt, muon_quality);

• "myOutputFileName" is the name of the output root tree.
• all_muons is a boolean variable indicating which tracks are going to be vertexed: true: all tracks; false only tracks matched to muons. By default all_muons = false.
• muon_pt is the minimum global muon pT in GeV/c, by default 1.5 GeV/c.
• muon_quality is the minimum quality, by default 0.

  The Muon quality is defined in d0root_analysis/objects/Muon.cpp:

In order to open the ROOT-tuple and plot the J/Psi invariant mass and lifetime, do:

 root myOutputFileName.root
 tree->Draw("PSI.mass","PSI.mass>2 && PSI.mass<4")
 tree->Draw("PSI.lifetime","PSI.mass>2.8 && PSI.mass<3.3")

Please send questions/comments/improvements/ or report problems to the

Back to Vertex fitting and finding in ROOT page