1 | /*
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2 | Example of using vertex fitter class to fit primary vertex
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3 | assumed to be generated in (0,0,0).
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4 | To run compiled version:
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5 | root
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6 | root> .L examples/LoadPvtxFit.C+
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7 | root> LoadPVtxFit()
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8 | root> ExamplePVtxFit("infile.root", Nevents)
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9 |
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10 | March 4, 2021
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11 | F. Bedeschi, INFN-Pisa, Italy
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12 | */
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13 |
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14 | #include "classes/DelphesClasses.h"
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15 | #include "external/ExRootAnalysis/ExRootTreeReader.h"
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16 | #include "modules/TrackCovariance.h"
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17 | #include "external/TrackCovariance/TrkUtil.h"
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18 | #include "external/TrackCovariance/VertexFit.h"
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19 |
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20 | #include <TClonesArray.h>
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21 | #include <TChain.h>
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22 | #include <TVectorD.h>
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23 | #include <TMatrixDSym.h>
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24 | #include <TH1.h>
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25 | #include <TCanvas.h>
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26 | #include <TStyle.h>
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27 |
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28 | //------------------------------------------------------------------------------
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29 |
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30 | void ExamplePVtxFit(const char* inputFile, Int_t Nevent = 5)
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31 | {
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32 | // Create chain of root trees
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33 | TChain chain("Delphes");
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34 | chain.Add(inputFile);
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35 |
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36 | // Create object of class ExRootTreeReader
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37 | ExRootTreeReader* treeReader = new ExRootTreeReader(&chain);
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38 | Long64_t numberOfEntries = treeReader->GetEntries();
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39 |
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40 | // Get pointers to branches used in this analysis
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41 | TClonesArray* branchGenPart = treeReader->UseBranch("Particle");
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42 | TClonesArray* branchTrack = treeReader->UseBranch("Track");
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43 |
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44 | // Book histograms
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45 | Int_t Nbin = 100;
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46 | TH1D* hXpull = new TH1D("hXpull", "Pull X vertex component", Nbin, -10., 10.);
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47 | TH1D* hYpull = new TH1D("hYpull", "Pull Y vertex component", Nbin, -10., 10.);
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48 | TH1D* hZpull = new TH1D("hZpull", "Pull Z vertex component", Nbin, -10., 10.);
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49 | TH1D* hChi2 = new TH1D("hChi2", "Vertex #chi^{2}/N_{dof}", Nbin, 0., 10.);
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50 | //
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51 | // Loop over all events
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52 | Int_t Nev = TMath::Min(Nevent, (Int_t) numberOfEntries);
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53 | for (Int_t entry = 0; entry < Nev; ++entry)
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54 | {
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55 | // Load selected branches with data from specified event
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56 | treeReader->ReadEntry(entry);
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57 | Int_t Ntr = 0; // # of tracks from primary vertex
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58 | Int_t NtrG = branchTrack->GetEntries(); // Total # of tracks
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59 | TVectorD** pr = new TVectorD * [NtrG];
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60 | TMatrixDSym** cv = new TMatrixDSym * [NtrG];
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61 | // If event contains at least 1 track
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62 | //
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63 | if (branchTrack->GetEntries() > 0)
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64 | {
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65 | // Loop on tracks
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66 | for (Int_t it = 0; it < branchTrack->GetEntries(); it++)
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67 | {
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68 | Track* trk = (Track*)branchTrack->At(it);
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69 | //
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70 | // Get associated generated particle
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71 | GenParticle* gp = (GenParticle*)trk->Particle.GetObject();
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72 | //
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73 | // Position of origin (mm)
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74 | Double_t x = gp->X;
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75 | Double_t y = gp->Y;
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76 | Double_t z = gp->Z;
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77 | //
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78 | // Select group of tracks originating from the primary vertex
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79 | if (x == 0.0 && y == 0.0)
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80 | {
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81 | //
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82 | // Reconstructed track parameters
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83 | Double_t obsD0 = trk->D0;
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84 | Double_t obsPhi = trk->Phi;
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85 | Double_t obsC = trk->C;
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86 | Double_t obsZ0 = trk->DZ;
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87 | Double_t obsCtg = trk->CtgTheta;
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88 | Double_t oPar[5] = { obsD0, obsPhi, obsC, obsZ0, obsCtg };
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89 | TVectorD obsPar(5, oPar); // Fill observed parameters
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90 | //
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91 | pr[Ntr] = new TVectorD(obsPar);
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92 | cv[Ntr] = new TMatrixDSym(TrkUtil::CovToMm(trk->CovarianceMatrix()));
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93 | Ntr++;
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94 | }
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95 | } // End loop on tracks
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96 | }
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97 | //
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98 | // Fit primary vertex
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99 | Int_t MinTrk = 2; // Minumum # tracks for vertex fit
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100 | if (Ntr >= MinTrk) {
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101 | VertexFit* Vtx = new VertexFit(Ntr, pr, cv);
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102 | TVectorD xvtx = Vtx->GetVtx();
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103 | TMatrixDSym covX = Vtx->GetVtxCov();
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104 | Double_t Chi2 = Vtx->GetVtxChi2();
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105 | Double_t Ndof = 2 * (Double_t)Ntr - 3;
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106 | Double_t PullX = xvtx(0) / TMath::Sqrt(covX(0, 0));
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107 | Double_t PullY = xvtx(1) / TMath::Sqrt(covX(1, 1));
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108 | Double_t PullZ = xvtx(2) / TMath::Sqrt(covX(2, 2));
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109 | //
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110 | // Fill histograms
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111 | hXpull->Fill(PullX);
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112 | hYpull->Fill(PullY);
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113 | hZpull->Fill(PullZ);
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114 | hChi2->Fill(Chi2 / Ndof);
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115 | }
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116 |
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117 | //
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118 | // Cleanup
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119 | for (Int_t i = 0; i < Ntr; i++) delete pr[i];
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120 | for (Int_t i = 0; i < Ntr; i++) delete cv[i];
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121 | delete[] pr;
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122 | delete[] cv;
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123 | }
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124 | //
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125 | // Show resulting histograms
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126 | //
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127 | TCanvas* Cnv = new TCanvas("Cnv", "Delphes primary vertex fit pulls", 50, 50, 900, 500);
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128 | Cnv->Divide(2, 2);
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129 | Cnv->cd(1); gPad->SetLogy(1); gStyle->SetOptFit(1111);
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130 | hXpull->Fit("gaus"); hXpull->Draw();
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131 | Cnv->cd(2); gPad->SetLogy(1); gStyle->SetOptFit(1111);
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132 | hYpull->Fit("gaus"); hYpull->Draw();
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133 | Cnv->cd(3); gPad->SetLogy(1); gStyle->SetOptFit(1111);
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134 | hZpull->Fit("gaus"); hZpull->Draw();
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135 | Cnv->cd(4); hChi2->Draw();
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136 | }
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