TrackTimeValueMapProducer.cc

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// This producer assigns vertex times (with a specified resolution) to tracks.
// The times are produced as valuemaps associated to tracks, so the track
// dataformat doesn't need to be modified.
 
#include "FWCore/Framework/interface/Frameworkfwd.h"
#include "FWCore/Framework/interface/global/EDProducer.h"
 
#include "FWCore/Framework/interface/Event.h"
#include "FWCore/Framework/interface/MakerMacros.h"
 
#include "FWCore/MessageLogger/interface/MessageLogger.h"
 
#include "DataFormats/Common/interface/ValueMap.h"
#include "DataFormats/Common/interface/View.h"
#include "DataFormats/Math/interface/deltaPhi.h"
 
#include "DataFormats/GsfTrackReco/interface/GsfTrack.h"
#include "DataFormats/GsfTrackReco/interface/GsfTrackFwd.h"
#include "DataFormats/TrackReco/interface/Track.h"
#include "DataFormats/TrackReco/interface/TrackFwd.h"
#include "MagneticField/Engine/interface/MagneticField.h"
#include "SimDataFormats/Associations/interface/TrackToTrackingParticleAssociator.h"
#include "SimDataFormats/PileupSummaryInfo/interface/PileupSummaryInfo.h"
#include "SimDataFormats/Track/interface/SimTrackContainer.h"
#include "SimDataFormats/TrackingAnalysis/interface/TrackingParticle.h"
#include "SimDataFormats/TrackingAnalysis/interface/TrackingVertex.h"
#include "SimDataFormats/TrackingAnalysis/interface/TrackingVertexContainer.h"
#include "SimDataFormats/Vertex/interface/SimVertexContainer.h"
#include "SimTracker/TrackerHitAssociation/interface/TrackerHitAssociator.h"
#include "TrackingTools/Records/interface/TransientTrackRecord.h"
#include "TrackingTools/TransientTrack/interface/TransientTrackBuilder.h"
 
#include <memory>
#include <random>
 
#include "CLHEP/Units/SystemOfUnits.h"
#include "FWCore/Utilities/interface/isFinite.h"
#include "FWCore/Utilities/interface/transform.h"
#include "SimTracker/TrackAssociation/interface/ResolutionModel.h"
 
class TrackTimeValueMapProducer : public edm::global::EDProducer<> {
public:
  TrackTimeValueMapProducer(const edm::ParameterSet &);
  ~TrackTimeValueMapProducer() override {}
 
  void produce(edm::StreamID, edm::Event &, const edm::EventSetup &) const override;
 
private:
  // inputs
  const edm::EDGetTokenT<edm::View<reco::Track>> tracks_;
  const std::string tracksName_;
  const edm::EDGetTokenT<TrackingParticleCollection> trackingParticles_;
  const edm::EDGetTokenT<TrackingVertexCollection> trackingVertices_;
  const edm::EDGetTokenT<std::vector<PileupSummaryInfo>> pileupSummaryInfo_;
  // tracking particle associators by order of preference
  const std::vector<edm::EDGetTokenT<reco::TrackToTrackingParticleAssociator>> associators_;
  // eta bounds
  const float etaMin_, etaMax_, ptMin_, pMin_, etaMaxForPtThreshold_;
  // options
  std::vector<std::unique_ptr<const ResolutionModel>> resolutions_;
  // functions
  float extractTrackVertexTime(const TrackingParticle &, const reco::TransientTrack &) const;
};
 
DEFINE_FWK_MODULE(TrackTimeValueMapProducer);
 
namespace {
  constexpr float m_pion = 139.57061e-3;
  const std::string resolution("Resolution");
 
  template <typename ParticleType, typename T>
  void writeValueMap(edm::Event &iEvent,
                     const edm::Handle<edm::View<ParticleType>> &handle,
                     const std::vector<T> &values,
                     const std::string &label) {
    std::unique_ptr<edm::ValueMap<T>> valMap(new edm::ValueMap<T>());
    typename edm::ValueMap<T>::Filler filler(*valMap);
    filler.insert(handle, values.begin(), values.end());
    filler.fill();
    iEvent.put(std::move(valMap), label);
  }
}  // namespace
 
TrackTimeValueMapProducer::TrackTimeValueMapProducer(const edm::ParameterSet &conf)
    : tracks_(consumes<edm::View<reco::Track>>(conf.getParameter<edm::InputTag>("trackSrc"))),
      tracksName_(conf.getParameter<edm::InputTag>("trackSrc").label()),
      trackingParticles_(consumes<TrackingParticleCollection>(conf.getParameter<edm::InputTag>("trackingParticleSrc"))),
      trackingVertices_(consumes<TrackingVertexCollection>(conf.getParameter<edm::InputTag>("trackingVertexSrc"))),
      pileupSummaryInfo_(
          consumes<std::vector<PileupSummaryInfo>>(conf.getParameter<edm::InputTag>("pileupSummaryInfo"))),
      associators_(edm::vector_transform(
          conf.getParameter<std::vector<edm::InputTag>>("associators"),
          [this](const edm::InputTag &tag) { return this->consumes<reco::TrackToTrackingParticleAssociator>(tag); })),
      etaMin_(conf.getParameter<double>("etaMin")),
      etaMax_(conf.getParameter<double>("etaMax")),
      ptMin_(conf.getParameter<double>("ptMin")),
      pMin_(conf.getParameter<double>("pMin")),
      etaMaxForPtThreshold_(conf.getParameter<double>("etaMaxForPtThreshold")) {
  // setup resolution models
  const std::vector<edm::ParameterSet> &resos = conf.getParameterSetVector("resolutionModels");
  for (const auto &reso : resos) {
    const std::string &name = reso.getParameter<std::string>("modelName");
    resolutions_.emplace_back(ResolutionModelFactory::get()->create(name, reso));
 
    // times and time resolutions for general tracks
    produces<edm::ValueMap<float>>(tracksName_ + name);
    produces<edm::ValueMap<float>>(tracksName_ + name + resolution);
  }
}
 
void TrackTimeValueMapProducer::produce(edm::StreamID sid, edm::Event &evt, const edm::EventSetup &es) const {
  // get sim track associators
  std::vector<edm::Handle<reco::TrackToTrackingParticleAssociator>> associators;
  for (const auto &token : associators_) {
    associators.emplace_back();
    auto &back = associators.back();
    evt.getByToken(token, back);
  }
 
  std::vector<float> generalTrackTimes;
 
  // get track collections
  edm::Handle<edm::View<reco::Track>> TrackCollectionH;
  evt.getByToken(tracks_, TrackCollectionH);
  const edm::View<reco::Track> &TrackCollection = *TrackCollectionH;
 
  // get tracking particle collections
  edm::Handle<TrackingParticleCollection> TPCollectionH;
  evt.getByToken(trackingParticles_, TPCollectionH);
 
  edm::Handle<std::vector<PileupSummaryInfo>> pileupSummaryH;
  evt.getByToken(pileupSummaryInfo_, pileupSummaryH);
 
  // transient track builder
  edm::ESHandle<TransientTrackBuilder> theB;
  es.get<TransientTrackRecord>().get("TransientTrackBuilder", theB);
 
  // associate the reco tracks / gsf Tracks
  std::vector<reco::RecoToSimCollection> associatedTracks;
  for (auto associator : associators) {
    associatedTracks.emplace_back(associator->associateRecoToSim(TrackCollectionH, TPCollectionH));
  }
 
  double sumSimTime = 0.;
  double sumSimTimeSq = 0.;
  int nsim = 0;
  for (const PileupSummaryInfo &puinfo : *pileupSummaryH) {
    if (puinfo.getBunchCrossing() == 0) {
      for (const float &time : puinfo.getPU_times()) {
        double simtime = time;
        sumSimTime += simtime;
        sumSimTimeSq += simtime * simtime;
        ++nsim;
      }
      break;
    }
  }
 
  double meanSimTime = sumSimTime / double(nsim);
  double varSimTime = sumSimTimeSq / double(nsim) - meanSimTime * meanSimTime;
  double rmsSimTime = std::sqrt(std::max(0.1 * 0.1, varSimTime));
  std::normal_distribution<float> gausSimTime(meanSimTime, rmsSimTime);
 
  // get event-based seed for RNG
  unsigned int runNum_uint = static_cast<unsigned int>(evt.id().run());
  unsigned int lumiNum_uint = static_cast<unsigned int>(evt.id().luminosityBlock());
  unsigned int evNum_uint = static_cast<unsigned int>(evt.id().event());
  unsigned int tkChi2_uint = uint32_t(TrackCollection.empty() ? 0 : TrackCollection.refAt(0)->chi2() / 0.01);
  std::uint32_t seed = tkChi2_uint + (lumiNum_uint << 10) + (runNum_uint << 20) + evNum_uint;
  std::mt19937 rng(seed);
 
  for (unsigned itk = 0; itk < TrackCollection.size(); ++itk) {
    const auto tkref = TrackCollection.refAt(itk);
    reco::RecoToSimCollection::const_iterator track_tps = associatedTracks.back().end();
 
    for (const auto &association : associatedTracks) {
      track_tps = association.find(tkref);
      if (track_tps != association.end())
        break;
    }
 
    if (track_tps != associatedTracks.back().end() && track_tps->val.size() == 1) {
      reco::TransientTrack tt = theB->build(*tkref);
      float time = extractTrackVertexTime(*track_tps->val[0].first, tt);
      generalTrackTimes.push_back(time);
    } else {
      float rndtime = gausSimTime(rng);
      generalTrackTimes.push_back(rndtime);
      if (track_tps != associatedTracks.back().end() && track_tps->val.size() > 1) {
        LogDebug("TooManyTracks") << "track matched to " << track_tps->val.size() << " tracking particles!"
                                  << std::endl;
      }
    }
  }
 
  for (const auto &reso : resolutions_) {
    const std::string &name = reso->name();
    std::vector<float> times, resos;
 
    times.reserve(TrackCollection.size());
    resos.reserve(TrackCollection.size());
 
    for (unsigned i = 0; i < TrackCollection.size(); ++i) {
      const reco::Track &tk = TrackCollection[i];
      const float absEta = std::abs(tk.eta());
      bool inAcceptance = absEta < etaMax_ && absEta >= etaMin_ && tk.p() > pMin_ &&
                          (absEta > etaMaxForPtThreshold_ || tk.pt() > ptMin_);
      if (inAcceptance) {
        const float resolution = reso->getTimeResolution(tk);
        std::normal_distribution<float> gausGeneralTime(generalTrackTimes[i], resolution);
        times.push_back(gausGeneralTime(rng));
        resos.push_back(resolution);
      } else {
        times.push_back(0.0f);
        resos.push_back(-1.);
      }
    }
 
    writeValueMap(evt, TrackCollectionH, times, tracksName_ + name);
    writeValueMap(evt, TrackCollectionH, resos, tracksName_ + name + resolution);
  }
}
 
float TrackTimeValueMapProducer::extractTrackVertexTime(const TrackingParticle &tp,
                                                        const reco::TransientTrack &tt) const {
  int pdgid = tp.pdgId();
  const auto &tvertex = tp.parentVertex();
  math::XYZTLorentzVectorD result = tvertex->position();
 
  // account for secondary vertices...
  if (tvertex->nSourceTracks() && tvertex->sourceTracks()[0]->pdgId() == pdgid) {
    auto pvertex = tvertex->sourceTracks()[0]->parentVertex();
    result = pvertex->position();
    while (pvertex->nSourceTracks() && pvertex->sourceTracks()[0]->pdgId() == pdgid) {
      pvertex = pvertex->sourceTracks()[0]->parentVertex();
      result = pvertex->position();
    }
  }
 
  float time = result.T() * CLHEP::second;
  // correct for time of flight from track reference position
  GlobalPoint result_pos(result.x(), result.y(), result.z());
  const auto &tkstate = tt.trajectoryStateClosestToPoint(result_pos);
  float tkphi = tkstate.momentum().phi();
  float tkz = tkstate.position().z();
  float dphi = reco::deltaPhi(tkphi, tt.track().phi());
  float dz = tkz - tt.track().vz();
 
  float radius = 100. * tt.track().pt() / (0.3 * tt.field()->inTesla(GlobalPoint(0, 0, 0)).z());
  float pathlengthrphi = tt.track().charge() * dphi * radius;
 
  float pathlength = std::sqrt(pathlengthrphi * pathlengthrphi + dz * dz);
  float p = tt.track().p();
 
  float speed = std::sqrt(1. / (1. + m_pion / p)) * CLHEP::c_light / CLHEP::cm;  // speed in cm/ns
  float dt = pathlength / speed;
 
  return time - dt;
}