PatBJetTrackAnalyzer.cc

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#include <algorithm>
#include <iostream>
#include <cmath>
#include <vector>
#include <string>

#include <TH1.h>
#include <TProfile.h>

#include <Math/VectorUtil.h>

#include "FWCore/Framework/interface/Frameworkfwd.h"
#include "FWCore/Framework/interface/Event.h"
#include "FWCore/Framework/interface/EventSetup.h"
#include "FWCore/Framework/interface/one/EDAnalyzer.h"
#include "FWCore/Utilities/interface/InputTag.h"
#include "FWCore/ParameterSet/interface/ParameterSet.h"
#include "FWCore/ServiceRegistry/interface/Service.h"

#include "CommonTools/UtilAlgos/interface/TFileService.h"

#include "DataFormats/BeamSpot/interface/BeamSpot.h"
#include "DataFormats/VertexReco/interface/Vertex.h"
#include "DataFormats/VertexReco/interface/VertexFwd.h"
#include "DataFormats/TrackReco/interface/Track.h"
#include "DataFormats/TrackReco/interface/TrackFwd.h"
#include "DataFormats/PatCandidates/interface/Jet.h"
#include "DataFormats/GeometryCommonDetAlgo/interface/Measurement1D.h"

class PatBJetTrackAnalyzer : public edm::one::EDAnalyzer<edm::one::SharedResources> {
public:
  PatBJetTrackAnalyzer(const edm::ParameterSet &params);
  ~PatBJetTrackAnalyzer() override;

  // virtual methods called from base class EDAnalyzer
  void beginJob() override;
  void analyze(const edm::Event &event, const edm::EventSetup &es) override;

private:
  // configuration parameters
  edm::EDGetTokenT<pat::JetCollection> jetsToken_;
  edm::EDGetTokenT<reco::TrackCollection> tracksToken_;
  edm::EDGetTokenT<reco::BeamSpot> beamSpotToken_;
  edm::EDGetTokenT<reco::VertexCollection> primaryVerticesToken_;

  double jetPtCut_;   // minimum (uncorrected) jet energy
  double jetEtaCut_;  // maximum |eta| for jet
  double maxDeltaR_;  // angle between jet and tracks

  double minPt_;               // track pt quality cut
  unsigned int minPixelHits_;  // minimum number of pixel hits
  unsigned int minTotalHits_;  // minimum number of total hits

  unsigned int nThTrack_;  // n-th hightest track to choose

  // jet flavour constants

  enum Flavour { ALL_JETS = 0, UDSG_JETS, C_JETS, B_JETS, NONID_JETS, N_JET_TYPES };

  TH1 *flavours_;

  // one group of plots per jet flavour;
  struct Plots {
    TH1 *allIP, *allIPErr, *allIPSig;
    TH1 *trackIP, *trackIPErr, *trackIPSig;
    TH1 *negativeIP, *negativeIPErr, *negativeIPSig;
    TH1 *nTracks, *allDeltaR;
  } plots_[N_JET_TYPES];
};

PatBJetTrackAnalyzer::PatBJetTrackAnalyzer(const edm::ParameterSet &params)
    : jetsToken_(consumes<pat::JetCollection>(params.getParameter<edm::InputTag>("jets"))),
      tracksToken_(consumes<reco::TrackCollection>(params.getParameter<edm::InputTag>("tracks"))),
      beamSpotToken_(consumes<reco::BeamSpot>(params.getParameter<edm::InputTag>("beamSpot"))),
      primaryVerticesToken_(consumes<reco::VertexCollection>(params.getParameter<edm::InputTag>("primaryVertices"))),
      jetPtCut_(params.getParameter<double>("jetPtCut")),
      jetEtaCut_(params.getParameter<double>("jetEtaCut")),
      maxDeltaR_(params.getParameter<double>("maxDeltaR")),
      minPt_(params.getParameter<double>("minPt")),
      minPixelHits_(params.getParameter<unsigned int>("minPixelHits")),
      minTotalHits_(params.getParameter<unsigned int>("minTotalHits")),
      nThTrack_(params.getParameter<unsigned int>("nThTrack")) {
  usesResource(TFileService::kSharedResource);
}

PatBJetTrackAnalyzer::~PatBJetTrackAnalyzer() {}

void PatBJetTrackAnalyzer::beginJob() {
  // retrieve handle to auxiliary service
  //  used for storing histograms into ROOT file
  edm::Service<TFileService> fs;

  flavours_ = fs->make<TH1F>("flavours", "jet flavours", 5, 0, 5);

  // book histograms for all jet flavours
  for (unsigned int i = 0; i < N_JET_TYPES; i++) {
    Plots &plots = plots_[i];
    const char *flavour, *name;

    switch ((Flavour)i) {
      case ALL_JETS:
        flavour = "all jets";
        name = "all";
        break;
      case UDSG_JETS:
        flavour = "light flavour jets";
        name = "udsg";
        break;
      case C_JETS:
        flavour = "charm jets";
        name = "c";
        break;
      case B_JETS:
        flavour = "bottom jets";
        name = "b";
        break;
      default:
        flavour = "unidentified jets";
        name = "ni";
        break;
    }

    plots.allIP =
        fs->make<TH1F>(Form("allIP_%s", name), Form("signed IP for all tracks in %s", flavour), 100, -0.1, 0.2);
    plots.allIPErr = fs->make<TH1F>(
        Form("allIPErr_%s", name), Form("error of signed IP for all tracks in %s", flavour), 100, 0, 0.05);
    plots.allIPSig = fs->make<TH1F>(
        Form("allIPSig_%s", name), Form("signed IP significance for all tracks in %s", flavour), 100, -10, 20);

    plots.trackIP = fs->make<TH1F>(
        Form("trackIP_%s", name), Form("signed IP for selected positive track in %s", flavour), 100, -0.1, 0.2);
    plots.trackIPErr = fs->make<TH1F>(Form("trackIPErr_%s", name),
                                      Form("error of signed IP for selected positive track in %s", flavour),
                                      100,
                                      0,
                                      0.05);
    plots.trackIPSig = fs->make<TH1F>(Form("trackIPSig_%s", name),
                                      Form("signed IP significance for selected positive track in %s", flavour),
                                      100,
                                      -10,
                                      20);

    plots.negativeIP = fs->make<TH1F>(
        Form("negativeIP_%s", name), Form("signed IP for selected negative track in %s", flavour), 100, -0.2, 0.1);
    plots.negativeIPErr = fs->make<TH1F>(Form("negativeIPErr_%s", name),
                                         Form("error of signed IP for selected negative track in %s", flavour),
                                         100,
                                         0,
                                         0.05);
    plots.negativeIPSig = fs->make<TH1F>(Form("negativeIPSig_%s", name),
                                         Form("signed IP significance for selected negative track in %s", flavour),
                                         100,
                                         -20,
                                         10);

    plots.nTracks = fs->make<TH1F>(Form("nTracks_%s", name), Form("number of usable tracks in %s", flavour), 30, 0, 30);
    plots.allDeltaR =
        fs->make<TH1F>(Form("allDeltaR_%s", name), Form("\\DeltaR between track and %s", flavour), 100, 0, 1);
  }
}

// helper function to sort the tracks by impact parameter significance

static bool significanceHigher(const Measurement1D &meas1, const Measurement1D &meas2) {
  return meas1.significance() > meas2.significance();
}

void PatBJetTrackAnalyzer::analyze(const edm::Event &event, const edm::EventSetup &es) {
  // handle to the primary vertex collection
  edm::Handle<reco::VertexCollection> pvHandle;
  event.getByToken(primaryVerticesToken_, pvHandle);

  // handle to the tracks collection
  edm::Handle<reco::TrackCollection> tracksHandle;
  event.getByToken(tracksToken_, tracksHandle);

  // handle to the jets collection
  edm::Handle<pat::JetCollection> jetsHandle;
  event.getByToken(jetsToken_, jetsHandle);

  // handle to the beam spot
  edm::Handle<reco::BeamSpot> beamSpot;
  event.getByToken(beamSpotToken_, beamSpot);

  // rare case of no reconstructed primary vertex
  if (pvHandle->empty())
    return;

  // extract the position of the (most probable) reconstructed vertex
  math::XYZPoint pv = (*pvHandle)[0].position();

  // now go through all jets
  for (pat::JetCollection::const_iterator jet = jetsHandle->begin(); jet != jetsHandle->end(); ++jet) {
    // only look at jets that pass the pt and eta cut
    if (jet->pt() < jetPtCut_ || std::abs(jet->eta()) > jetEtaCut_)
      continue;

    Flavour flavour;
    // find out the jet flavour (differs between quark and anti-quark)
    switch (std::abs(jet->partonFlavour())) {
      case 1:
      case 2:
      case 3:
      case 21:
        flavour = UDSG_JETS;
        break;
      case 4:
        flavour = C_JETS;
        break;
      case 5:
        flavour = B_JETS;
        break;
      default:
        flavour = NONID_JETS;
    }

    // simply count the number of accepted jets
    flavours_->Fill(ALL_JETS);
    flavours_->Fill(flavour);

    // this vector will contain IP value / error pairs
    std::vector<Measurement1D> ipValErr;

    // Note: PAT is also able to store associated tracks
    //       within the jet object, so we don't have to do the
    //       matching ourselves
    // (see ->associatedTracks() method)
    // However, using this we can't play with the DeltaR cone
    // withour rerunning the PAT producer

    // now loop through all tracks
    for (reco::TrackCollection::const_iterator track = tracksHandle->begin(); track != tracksHandle->end(); ++track) {
      // check the quality criteria
      if (track->pt() < minPt_ || track->hitPattern().numberOfValidHits() < (int)minTotalHits_ ||
          track->hitPattern().numberOfValidPixelHits() < (int)minPixelHits_)
        continue;

      // check the Delta R between jet axis and track
      // (Delta_R^2 = Delta_Eta^2 + Delta_Phi^2)
      double deltaR = ROOT::Math::VectorUtil::DeltaR(jet->momentum(), track->momentum());

      plots_[ALL_JETS].allDeltaR->Fill(deltaR);
      plots_[flavour].allDeltaR->Fill(deltaR);

      // only look at tracks in jet cone
      if (deltaR > maxDeltaR_)
        continue;

      // What follows here is an approximation!
      //
      // The dxy() method of the tracks does a linear
      // extrapolation from the track reference position
      // given as the closest point to the beam spot
      // with respect to the given vertex.
      // Since we are using primary vertices, this
      // approximation works well
      //
      // In order to get better results, the
      // "TransientTrack" and specialised methods have
      // to be used.
      // Or look at the "impactParameterTagInfos",
      // which contains the precomputed information
      // from the official b-tagging algorithms
      //
      // see ->tagInfoTrackIP() method

      double ipError = track->dxyError();
      double ipValue = std::abs(track->dxy(pv));

      // in order to compute the sign, we check if
      // the point of closest approach to the vertex
      // is in front or behind the vertex.
      // Again, we a linear approximation
      //
      // dot product between reference point and jet axis

      math::XYZVector closestPoint = track->referencePoint() - beamSpot->position();
      // only interested in transverse component, z -> 0
      closestPoint.SetZ(0.);
      double sign = closestPoint.Dot(jet->momentum());

      if (sign < 0)
        ipValue = -ipValue;

      ipValErr.push_back(Measurement1D(ipValue, ipError));
    }

    // now order all tracks by significance (highest first)
    std::sort(ipValErr.begin(), ipValErr.end(), significanceHigher);

    plots_[ALL_JETS].nTracks->Fill(ipValErr.size());
    plots_[flavour].nTracks->Fill(ipValErr.size());

    // plot all tracks

    for (std::vector<Measurement1D>::const_iterator iter = ipValErr.begin(); iter != ipValErr.end(); ++iter) {
      plots_[ALL_JETS].allIP->Fill(iter->value());
      plots_[flavour].allIP->Fill(iter->value());

      plots_[ALL_JETS].allIPErr->Fill(iter->error());
      plots_[flavour].allIPErr->Fill(iter->error());

      // significance (is really just value / error)
      plots_[ALL_JETS].allIPSig->Fill(iter->significance());
      plots_[flavour].allIPSig->Fill(iter->significance());
    }

    // check if we have enough tracks to fulfill the
    // n-th track requirement
    if (ipValErr.size() < nThTrack_)
      continue;

    // pick the n-th highest track
    const Measurement1D *trk = &ipValErr[nThTrack_ - 1];

    plots_[ALL_JETS].trackIP->Fill(trk->value());
    plots_[flavour].trackIP->Fill(trk->value());

    plots_[ALL_JETS].trackIPErr->Fill(trk->error());
    plots_[flavour].trackIPErr->Fill(trk->error());

    plots_[ALL_JETS].trackIPSig->Fill(trk->significance());
    plots_[flavour].trackIPSig->Fill(trk->significance());

    // here we define a "negative tagger", i.e. we take
    // the track with the n-lowest signed IP
    // (i.e. preferrably select tracks that appear to become
    //  from "behind" the primary vertex, supposedly mismeasured
    //  tracks really coming from the primary vertex, and
    //  the contamination of displaced tracks should be small)
    trk = &ipValErr[ipValErr.size() - nThTrack_];

    plots_[ALL_JETS].negativeIP->Fill(trk->value());
    plots_[flavour].negativeIP->Fill(trk->value());

    plots_[ALL_JETS].negativeIPErr->Fill(trk->error());
    plots_[flavour].negativeIPErr->Fill(trk->error());

    plots_[ALL_JETS].negativeIPSig->Fill(trk->significance());
    plots_[flavour].negativeIPSig->Fill(trk->significance());
  }
}

#include "FWCore/Framework/interface/MakerMacros.h"

DEFINE_FWK_MODULE(PatBJetTrackAnalyzer);