TrackerSimHitProducer.cc

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#include <vector>
#include <memory>

// framework
#include "FWCore/Framework/interface/Event.h"
#include "FWCore/ParameterSet/interface/ParameterSet.h"
#include "MagneticField/UniformEngine/interface/UniformMagneticField.h"

// tracking
#include "TrackingTools/DetLayers/interface/DetLayer.h"
#include "TrackingTools/GeomPropagators/interface/AnalyticalPropagator.h"
#include "TrackingTools/TrajectoryState/interface/TrajectoryStateOnSurface.h"
#include "TrackingTools/GeomPropagators/interface/AnalyticalPropagator.h"
#include "TrackingTools/GeomPropagators/interface/HelixArbitraryPlaneCrossing.h"

// fastsim
#include "FastSimulation/TrajectoryManager/interface/InsideBoundsMeasurementEstimator.h" //TODO move this
#include "FastSimulation/SimplifiedGeometryPropagator/interface/Particle.h"
#include "FastSimulation/SimplifiedGeometryPropagator/interface/SimplifiedGeometry.h"
#include "FastSimulation/SimplifiedGeometryPropagator/interface/InteractionModel.h"
#include "FastSimulation/SimplifiedGeometryPropagator/interface/InteractionModelFactory.h"
#include "FastSimulation/SimplifiedGeometryPropagator/interface/Constants.h"

// data formats
#include "DataFormats/GeometrySurface/interface/Plane.h"
#include "DataFormats/GeometryVector/interface/GlobalVector.h"
#include "DataFormats/GeometryVector/interface/GlobalPoint.h"
#include "DataFormats/GeometryVector/interface/LocalVector.h"
#include "DataFormats/GeometryVector/interface/LocalPoint.h"
#include "SimDataFormats/TrackingHit/interface/PSimHit.h"
#include "SimDataFormats/TrackingHit/interface/PSimHitContainer.h"

// other
#include "Geometry/CommonDetUnit/interface/GeomDet.h"
#include "CondFormats/External/interface/DetID.h"
#include "FWCore/Framework/interface/ProducerBase.h"


// Author: L. Vanelderen, S. Kurz
// Date: 29 May 2017


typedef std::pair<const GeomDet*,TrajectoryStateOnSurface> DetWithState;

namespace fastsim
{

    class TrackerSimHitProducer : public InteractionModel
    {
        public:
        TrackerSimHitProducer(const std::string & name,const edm::ParameterSet & cfg);

        ~TrackerSimHitProducer() override{;}


        void interact(Particle & particle,const SimplifiedGeometry & layer,std::vector<std::unique_ptr<Particle> > & secondaries,const RandomEngineAndDistribution & random) override;
        
        void registerProducts(edm::ProducerBase & producer) const override;

        void storeProducts(edm::Event & iEvent) override;


        std::pair<double, PSimHit*> createHitOnDetector(const TrajectoryStateOnSurface & particle, int pdgId, double layerThickness, double eLoss, int simTrackId, const GeomDet & detector, GlobalPoint & refPos);
        
        private:
        const double onSurfaceTolerance_;  
        std::unique_ptr<edm::PSimHitContainer> simHitContainer_;  
        double minMomentum_;  
        bool doHitsFromInboundParticles_;  
    };
}



fastsim::TrackerSimHitProducer::TrackerSimHitProducer(const std::string & name,const edm::ParameterSet & cfg)
    : fastsim::InteractionModel(name)
    , onSurfaceTolerance_(0.01)
    , simHitContainer_(new edm::PSimHitContainer)
{
    // Set the minimal momentum
    minMomentum_ = cfg.getParameter<double>("minMomentumCut");
    // - if not set, particles from outside the beampipe with a negative speed in R direction are propagated but no SimHits
    // - particle with positive (negative) z and negative (positive) speed in z direction: no SimHits
    // -> this is not neccesary since a track reconstruction is not possible in this case anyways
    doHitsFromInboundParticles_ = cfg.getParameter<bool>("doHitsFromInboundParticles");
}

void fastsim::TrackerSimHitProducer::registerProducts(edm::ProducerBase & producer) const
{
    producer.produces<edm::PSimHitContainer>("TrackerHits");
}

void fastsim::TrackerSimHitProducer::storeProducts(edm::Event & iEvent)
{
    iEvent.put(std::move(simHitContainer_), "TrackerHits");
    simHitContainer_.reset(new edm::PSimHitContainer);
}

void fastsim::TrackerSimHitProducer::interact(Particle & particle,const SimplifiedGeometry & layer,std::vector<std::unique_ptr<Particle> > & secondaries,const RandomEngineAndDistribution & random)
{
    // the energy deposit in the layer
    double energyDeposit = particle.getEnergyDeposit();
    particle.setEnergyDeposit(0);

    //
    // don't save hits from particle that did a loop or are inbound (coming from the outer part of the tracker, going towards the center)
    //
    if(!doHitsFromInboundParticles_){
        if(particle.isLooper()){
            return;
        }    
        if(particle.momentum().X()*particle.position().X() + particle.momentum().Y()*particle.position().Y() < 0){
            particle.setLooper();
            return;
        }
        if(layer.isForward() && ((particle.position().Z() > 0 && particle.momentum().Z() < 0) || (particle.position().Z() < 0 && particle.momentum().Z() > 0))){
            particle.setLooper();
            return;
        }
    }

    //
    // check that layer has tracker modules
    //
    if(!layer.getDetLayer())
    {
    return;
    }

    //
    // no material
    //
    if(layer.getThickness(particle.position(), particle.momentum()) < 1E-10)
    {
    return;
    }

    //
    // only charged particles
    //
    if(particle.charge()==0)
    {
    return;
    }

    //
    // save hit only if momentum higher than threshold
    //
    if(particle.momentum().Perp2() < minMomentum_*minMomentum_)
    {
    return;
    }

    // create the trajectory of the particle
    UniformMagneticField magneticField(layer.getMagneticFieldZ(particle.position())); 
    GlobalPoint  position( particle.position().X(), particle.position().Y(), particle.position().Z());
    GlobalVector momentum( particle.momentum().Px(), particle.momentum().Py(), particle.momentum().Pz());
    auto plane = layer.getDetLayer()->surface().tangentPlane(position);
    TrajectoryStateOnSurface trajectory(GlobalTrajectoryParameters( position, momentum, TrackCharge( particle.charge()), &magneticField), *plane);
    
    // find detectors compatible with the particle's trajectory
    AnalyticalPropagator propagator(&magneticField, anyDirection);
    InsideBoundsMeasurementEstimator est;
    std::vector<DetWithState> compatibleDetectors = layer.getDetLayer()->compatibleDets(trajectory, propagator, est);

    // You have to sort the simHits in the order they occur!

    // The old algorithm (sorting by distance to IP) doesn't seem to make sense to me (what if particle moves inwards?)

    // Detector layers have to be sorted by proximity to particle.position
    // Propagate particle backwards a bit to make sure it's outside any components
    std::map<double, PSimHit*> distAndHits;
    // Position relative to which the hits should be sorted
    GlobalPoint positionOutside(particle.position().x()-particle.momentum().x()/particle.momentum().P()*10.,
                                particle.position().y()-particle.momentum().y()/particle.momentum().P()*10.,
                                particle.position().z()-particle.momentum().z()/particle.momentum().P()*10.);

    // FastSim: cheat tracking -> assign hits to closest charged daughter if particle decays
    int pdgId = particle.getMotherDeltaR() == -1 ? particle.pdgId() : particle.getMotherPdgId();

    // loop over the compatible detectors
    for (const auto & detectorWithState : compatibleDetectors)
    {
        const GeomDet & detector = *detectorWithState.first;
        const TrajectoryStateOnSurface & particleState = detectorWithState.second;

        // if the detector has no components
        if(detector.isLeaf())
        {
            std::pair<double, PSimHit*> hitPair = createHitOnDetector(particleState, pdgId, layer.getThickness(particle.position()), energyDeposit, particle.simTrackIndex(), detector, positionOutside);
            if(hitPair.second){
                distAndHits.insert(distAndHits.end(), hitPair);
            }
        }
        else
        {
            // if the detector has components
            for(const auto component : detector.components())
            {
                std::pair<double, PSimHit*> hitPair = createHitOnDetector(particleState, pdgId,layer.getThickness(particle.position()), energyDeposit, particle.simTrackIndex(), *component, positionOutside);            
                if(hitPair.second){
                    distAndHits.insert(distAndHits.end(), hitPair);
                }
            }
        }
    }

    // Fill simHitContainer
    for(std::map<double, PSimHit*>::const_iterator it = distAndHits.begin(); it != distAndHits.end(); it++){
        simHitContainer_->push_back(*(it->second));
    }
    
}

// Also returns distance to simHit since hits have to be ordered (in time) afterwards. Necessary to do explicit copy of TrajectoryStateOnSurface particle (not call by reference)
std::pair<double, PSimHit*> fastsim::TrackerSimHitProducer::createHitOnDetector(const TrajectoryStateOnSurface & particle, int pdgId, double layerThickness, double eLoss, int simTrackId, const GeomDet & detector, GlobalPoint & refPos)
{
    // determine position and momentum of particle in the coordinate system of the detector
    LocalPoint localPosition;
    LocalVector localMomentum;

    // if the particle is close enough, no further propagation is needed
    if(fabs(detector.toLocal(particle.globalPosition()).z()) < onSurfaceTolerance_) 
    {
       localPosition = particle.localPosition();
       localMomentum = particle.localMomentum();
    }
    // else, propagate 
    else 
    {
        // find crossing of particle with detector layer
        HelixArbitraryPlaneCrossing crossing(particle.globalPosition().basicVector(),
                              particle.globalMomentum().basicVector(),
                              particle.transverseCurvature(),
                              anyDirection);
        std::pair<bool,double> path = crossing.pathLength(detector.surface());
        // case propagation succeeds
        if (path.first)     
        {
            localPosition = detector.toLocal( GlobalPoint( crossing.position(path.second)));
            localMomentum = detector.toLocal( GlobalVector( crossing.direction(path.second)));
            localMomentum = localMomentum.unit() * particle.localMomentum().mag();
        }
        // case propagation fails
        else
        {
            return std::pair<double, PSimHit*>(0, nullptr);
        }
    }

    // find entry and exit point of particle in detector
    const Plane& detectorPlane = detector.surface();
    double halfThick = 0.5 * detectorPlane.bounds().thickness();
    double pZ = localMomentum.z();
    LocalPoint entry = localPosition + (-halfThick / pZ) * localMomentum;
    LocalPoint exit = localPosition + (halfThick / pZ) * localMomentum;
    double tof = particle.globalPosition().mag() / fastsim::Constants::speedOfLight ; // in nanoseconds
    
    // make sure the simhit is physically on the module
    double boundX = detectorPlane.bounds().width() / 2.;
    double boundY = detectorPlane.bounds().length() / 2.;
    // Special treatment for TID and TEC trapeziodal modules
    unsigned subdet = DetId(detector.geographicalId()).subdetId(); 
    if (subdet == 4 || subdet == 6) 
    boundX *=  1. - localPosition.y() / detectorPlane.position().perp();
    if(fabs(localPosition.x()) > boundX  || fabs(localPosition.y()) > boundY )
    {
       return std::pair<double, PSimHit*>(0, nullptr);
    }

    // Create the hit: the energy loss rescaled to the module thickness
    // Total thickness is in radiation lengths, 1 radlen = 9.36 cm
    // Sensitive module thickness is about 30 microns larger than 
    // the module thickness itself
    eLoss *= (2. * halfThick - 0.003) / (9.36 * layerThickness);

    // Position of the hit in global coordinates
    GlobalPoint hitPos(detector.surface().toGlobal(localPosition));

    return std::pair<double, PSimHit*>((hitPos-refPos).mag(),
                                        new PSimHit(entry, exit, localMomentum.mag(), tof, eLoss, pdgId,
                                                   detector.geographicalId().rawId(), simTrackId,
                                                   localMomentum.theta(),
                                                   localMomentum.phi()));
}

DEFINE_EDM_PLUGIN(
    fastsim::InteractionModelFactory,
    fastsim::TrackerSimHitProducer,
    "fastsim::TrackerSimHitProducer"
    );