/data/refman/pasoursint/CMSSW_4_1_8_patch12/src/FastSimulation/MuonSimHitProducer/src/MuonSimHitProducer.cc

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//
// Package:    MuonSimHitProducer
// Class:      MuonSimHitProducer
// 
//
// Original Author:  Martijn Mulders/Matthew Jones
//         Created:  Wed Jul 30 11:37:24 CET 2007
//         Working:  Fri Nov  9 09:39:33 CST 2007
//
// $Id: MuonSimHitProducer.cc,v 1.34 2010/07/26 14:07:00 aperrott Exp $
//
//

// CMSSW headers 
#include "FWCore/ServiceRegistry/interface/Service.h"
#include "FWCore/Utilities/interface/RandomNumberGenerator.h"
#include "FWCore/Framework/interface/MakerMacros.h"

// Fast Simulation headers
#include "FastSimulation/Utilities/interface/RandomEngine.h"
#include "FastSimulation/MuonSimHitProducer/interface/MuonSimHitProducer.h"
#include "FastSimulation/MaterialEffects/interface/MaterialEffects.h"
#include "FastSimulation/MaterialEffects/interface/MultipleScatteringSimulator.h"
#include "FastSimulation/MaterialEffects/interface/EnergyLossSimulator.h"
#include "FastSimulation/ParticlePropagator/interface/ParticlePropagator.h"

// SimTrack
#include "SimDataFormats/Track/interface/SimTrack.h"
#include "SimDataFormats/Vertex/interface/SimVertex.h"
#include "SimDataFormats/TrackingHit/interface/PSimHitContainer.h"

// STL headers 
#include <vector>
#include <iostream>

// RecoMuon headers
#include "RecoMuon/TrackingTools/interface/MuonServiceProxy.h"
#include "RecoMuon/Navigation/interface/DirectMuonNavigation.h"
#include "RecoMuon/MeasurementDet/interface/MuonDetLayerMeasurements.h"
#include "RecoMuon/TrackingTools/interface/MuonPatternRecoDumper.h"

// Tracking Tools
#include "TrackingTools/GeomPropagators/interface/HelixArbitraryPlaneCrossing.h"
#include "TrackPropagation/SteppingHelixPropagator/interface/SteppingHelixPropagator.h"

// Data Formats
#include "DataFormats/MuonDetId/interface/DTWireId.h"
#include "DataFormats/GeometrySurface/interface/PlaneBuilder.h"
#include "DataFormats/GeometrySurface/interface/TangentPlane.h"


// Geometry, Magnetic Field
#include "Geometry/DTGeometry/interface/DTGeometry.h"
#include "Geometry/CSCGeometry/interface/CSCGeometry.h"
#include "Geometry/RPCGeometry/interface/RPCGeometry.h"
#include "Geometry/Records/interface/MuonGeometryRecord.h"
#include "MagneticField/Records/interface/IdealMagneticFieldRecord.h"


// #include "TrackingTools/TrackAssociator/interface/TrackDetectorAssociator.h"

//for debug only 
//#define FAMOS_DEBUG

//
// constructors and destructor
//
MuonSimHitProducer::MuonSimHitProducer(const edm::ParameterSet& iConfig):
  theEstimator(iConfig.getParameter<double>("Chi2EstimatorCut")),
  propagatorWithoutMaterial(0)
 {

  //
  //  Initialize the random number generator service
  //
  edm::Service<edm::RandomNumberGenerator> rng;
  if ( ! rng.isAvailable() ) {
    throw cms::Exception("Configuration") <<
      "MuonSimHitProducer requires the RandomGeneratorService \n"
      "which is not present in the configuration file. \n"
      "You must add the service in the configuration file\n"
      "or remove the module that requires it.";
  }

  random = new RandomEngine(&(*rng));

  // Read relevant parameters
  readParameters(iConfig.getParameter<edm::ParameterSet>("MUONS"),
                 iConfig.getParameter<edm::ParameterSet>("TRACKS"),
                 iConfig.getParameter<edm::ParameterSet>("MaterialEffectsForMuons"));

  //
  //  register your products ... need to declare at least one possible product...
  //
  produces<edm::PSimHitContainer>("MuonCSCHits");
  produces<edm::PSimHitContainer>("MuonDTHits");
  produces<edm::PSimHitContainer>("MuonRPCHits");

  edm::ParameterSet serviceParameters =
     iConfig.getParameter<edm::ParameterSet>("ServiceParameters");
  theService = new MuonServiceProxy(serviceParameters);
}

// ---- method called once each job just before starting event loop ----
void 
MuonSimHitProducer::beginRun(edm::Run & run, const edm::EventSetup & es) {

  //services
  edm::ESHandle<MagneticField>          magField;
  edm::ESHandle<DTGeometry>             dtGeometry;
  edm::ESHandle<CSCGeometry>            cscGeometry;
  edm::ESHandle<RPCGeometry>            rpcGeometry;
  edm::ESHandle<Propagator>             propagator;

  es.get<IdealMagneticFieldRecord>().get(magField);
  es.get<MuonGeometryRecord>().get("MisAligned",dtGeometry);
  es.get<MuonGeometryRecord>().get("MisAligned",cscGeometry);
  es.get<MuonGeometryRecord>().get(rpcGeometry);

  magfield = &(*magField);
  dtGeom = &(*dtGeometry);
  cscGeom = &(*cscGeometry);
  rpcGeom = &(*rpcGeometry);

  theService->update(es);

  // A few propagators
  propagatorWithMaterial = &(*(theService->propagator("SteppingHelixPropagatorAny")));
  propagatorWithoutMaterial = propagatorWithMaterial->clone();
  SteppingHelixPropagator* SHpropagator = dynamic_cast<SteppingHelixPropagator*> (propagatorWithoutMaterial); // Beuark!
  SHpropagator->setMaterialMode(true); // switches OFF material effects;

}
  
MuonSimHitProducer::~MuonSimHitProducer()
{
  // do anything here that needs to be done at destruction time
  // (e.g. close files, deallocate resources etc.)
  
  if ( random ) { 
    delete random;
  }

  if ( theMaterialEffects ) delete theMaterialEffects;
  if ( propagatorWithoutMaterial) delete propagatorWithoutMaterial;
}


//
// member functions
//

// ------------ method called to produce the data  ------------

void 
MuonSimHitProducer::produce(edm::Event& iEvent,const edm::EventSetup& iSetup) {
  // using namespace edm;
  // using namespace std;

  MuonPatternRecoDumper dumper;

  edm::Handle<std::vector<SimTrack> > simMuons;
  edm::Handle<std::vector<SimVertex> > simVertices;
  std::vector<PSimHit> theCSCHits;
  std::vector<PSimHit> theDTHits;
  std::vector<PSimHit> theRPCHits;

  DirectMuonNavigation navigation(theService->detLayerGeometry());
  iEvent.getByLabel(theSimModuleLabel_,theSimModuleProcess_,simMuons);
  iEvent.getByLabel(theSimModuleLabel_,simVertices);

  for ( unsigned int itrk=0; itrk<simMuons->size(); itrk++ ) {
    const SimTrack &mySimTrack = (*simMuons)[itrk];
    math::XYZTLorentzVector mySimP4(mySimTrack.momentum().x(),
                                    mySimTrack.momentum().y(),
                                    mySimTrack.momentum().z(),
                                    mySimTrack.momentum().t());

    // Decaying hadrons are now in the list, and so are their muon daughter
    // Ignore the hadrons here.
    int pid = mySimTrack.type(); 
    if ( abs(pid) != 13 ) continue;

    double t0 = 0;
    GlobalPoint initialPosition;
    int ivert = mySimTrack.vertIndex();
    if ( ivert >= 0 ) {
      t0 = (*simVertices)[ivert].position().t();
      GlobalPoint xyzzy((*simVertices)[ivert].position().x(),
                        (*simVertices)[ivert].position().y(),
                        (*simVertices)[ivert].position().z());
      initialPosition = xyzzy;
    }
//
//  Presumably t0 has dimensions of cm if not mm?
//  Convert to ns for internal calculations.
//  I wonder where we should get c from?
//
    double tof = t0/29.98;

#ifdef FAMOS_DEBUG
    std::cout << " ===> MuonSimHitProducer::reconstruct() found SIMTRACK - pid = "
              << pid ;
    std::cout << " : pT = " << mySimP4.Pt()
              << ", eta = " << mySimP4.Eta()
              << ", phi = " << mySimP4.Phi() << std::endl;
#endif

//
//  Produce muons sim hits starting from undecayed simulated muons
//

    GlobalPoint startingPosition(mySimTrack.trackerSurfacePosition().x(),
                                 mySimTrack.trackerSurfacePosition().y(),
                                 mySimTrack.trackerSurfacePosition().z());
    GlobalVector startingMomentum(mySimTrack.trackerSurfaceMomentum().x(),
                                  mySimTrack.trackerSurfaceMomentum().y(),
                                  mySimTrack.trackerSurfaceMomentum().z());
//
//  Crap... there's no time-of-flight to the trackerSurfacePosition()...
//  So, this will be wrong when the curvature can't be neglected, but that
//  will be rather seldom...  May as well ignore the mass too.
//
    GlobalVector dtracker = startingPosition-initialPosition;
    tof += dtracker.mag()/29.98;

#ifdef FAMOS_DEBUG
    std::cout << " the Muon START position " << startingPosition << std::endl;
    std::cout << " the Muon START momentum " << startingMomentum << std::endl;
#endif

// 
//  Some magic to define a TrajectoryStateOnSurface
//
    PlaneBuilder pb;
    GlobalVector zAxis = startingMomentum.unit();
    GlobalVector yAxis(zAxis.y(),-zAxis.x(),0); 
    GlobalVector xAxis = yAxis.cross(zAxis);
    Surface::RotationType rot = Surface::RotationType(xAxis,yAxis,zAxis);
    PlaneBuilder::ReturnType startingPlane = pb.plane(startingPosition,rot);
    GlobalTrajectoryParameters gtp(startingPosition,
                                   startingMomentum,
                                   (int)mySimTrack.charge(),
                                   magfield);
    TrajectoryStateOnSurface startingState(gtp,*startingPlane);

    std::vector<const DetLayer *> navLayers;
    if ( fabs(startingState.globalMomentum().eta()) > 4.5 ) {
      navLayers = navigation.compatibleEndcapLayers(*(startingState.freeState()),
                                                    alongMomentum);
    }
    else {
      navLayers = navigation.compatibleLayers(*(startingState.freeState()),
                                               alongMomentum);
    }
    /*
    edm::ESHandle<Propagator> propagator =
      theService->propagator("SteppingHelixPropagatorAny");
    */

    if ( navLayers.empty() ) continue;

#ifdef FAMOS_DEBUG
      std::cout << "Found " << navLayers.size()
                << " compatible DetLayers..." << std::endl;
#endif

    TrajectoryStateOnSurface propagatedState = startingState;
    for ( unsigned int ilayer=0; ilayer<navLayers.size(); ilayer++ ) {

#ifdef FAMOS_DEBUG
      std::cout << "Propagating to layer " << ilayer << " " 
                << dumper.dumpLayer(navLayers[ilayer]) 
                << std::endl;
#endif
      
      std::vector<DetWithState> comps = 
        navLayers[ilayer]->compatibleDets(propagatedState,*propagatorWithMaterial,theEstimator);
      if ( comps.empty() ) continue;

#ifdef FAMOS_DEBUG
      std::cout << "Propagating " << propagatedState << std::endl;
#endif

      // Starting momentum
      double pi = propagatedState.globalMomentum().mag(); 

      // Propagate with material effects (dE/dx average only)
      SteppingHelixStateInfo shsStart(*(propagatedState.freeTrajectoryState()));
      const SteppingHelixStateInfo& shsDest = 
        ((const SteppingHelixPropagator*)propagatorWithMaterial)->propagate(shsStart,navLayers[ilayer]->surface());
      std::pair<TrajectoryStateOnSurface,double> next(shsDest.getStateOnSurface(navLayers[ilayer]->surface()),
                                                      shsDest.path());
      // No need to continue if there is no valid propagation available.
      // This happens rarely (~0.1% of ttbar events)
      if ( !next.first.isValid() ) continue; 
      // This is the estimate of the number of radiation lengths traversed, 
      // together with the total path length 
      double radPath = shsDest.radPath();
      double pathLength = next.second;

      // Now propagate without dE/dx (average) 
      // [To add the dE/dx fluctuations to the actual dE/dx]
      std::pair<TrajectoryStateOnSurface,double> nextNoMaterial = 
        propagatorWithoutMaterial->propagateWithPath(propagatedState,navLayers[ilayer]->surface());

      // Update the propagated state
      propagatedState = next.first;
      double pf = propagatedState.globalMomentum().mag();

      // Insert dE/dx fluctuations and multiple scattering
      // Skip this step if nextNoMaterial.first is not valid 
      // This happens rarely (~0.02% of ttbar events)
      if ( theMaterialEffects && nextNoMaterial.first.isValid() ) applyMaterialEffects(propagatedState,nextNoMaterial.first,radPath);
      // Check that the 'shaken' propagatedState is still valid, otherwise continue
      if ( !propagatedState.isValid() ) continue; 
      // (No evidence that this ever happens)
//
//  Consider this... 1 GeV muon has a velocity that is only 0.5% slower than c...
//  We probably can safely ignore the mass for anything that makes it out to the
//  muon chambers.
//
      double pavg = 0.5*(pi+pf);
      double m = mySimP4.M();
      double rbeta = sqrt(1+m*m/(pavg*pavg))/29.98;
      double dtof = pathLength*rbeta;

#ifdef FAMOS_DEBUG
      std::cout << "Propagated to next surface... path length = " << pathLength 
                << " cm, dTOF = " << dtof << " ns" << std::endl;
#endif

      tof += dtof;

      for ( unsigned int icomp=0; icomp<comps.size(); icomp++ )
        {
      const GeomDet *gd = comps[icomp].first;
      if ( gd->subDetector() == GeomDetEnumerators::DT ) {
        DTChamberId id(gd->geographicalId());
        const DTChamber *chamber = dtGeom->chamber(id);
        std::vector<const DTSuperLayer *> superlayer = chamber->superLayers();
        for ( unsigned int isl=0; isl<superlayer.size(); isl++ ) {
          std::vector<const DTLayer *> layer = superlayer[isl]->layers();
          for ( unsigned int ilayer=0; ilayer<layer.size(); ilayer++ ) {
            DTLayerId lid = layer[ilayer]->id();
#ifdef FAMOS_DEBUG
            std::cout << "    Extrapolated to DT (" 
                      << lid.wheel() << "," 
                      << lid.station() << "," 
                      << lid.sector() << "," 
                      << lid.superlayer() << "," 
                      << lid.layer() << ")" << std::endl;
#endif

            const GeomDetUnit *det = dtGeom->idToDetUnit(lid);

            HelixArbitraryPlaneCrossing crossing(propagatedState.globalPosition().basicVector(),
                                                 propagatedState.globalMomentum().basicVector(),
                                                 propagatedState.transverseCurvature(),
                                                 anyDirection);
            std::pair<bool,double> path = crossing.pathLength(det->surface());
            if ( ! path.first ) continue;
            LocalPoint lpos = det->toLocal(GlobalPoint(crossing.position(path.second)));
            if ( ! det->surface().bounds().inside(lpos) ) continue;
            const DTTopology& dtTopo = layer[ilayer]->specificTopology();
            int wire = dtTopo.channel(lpos);
            if (wire < dtTopo.firstChannel() || wire > dtTopo.lastChannel()) continue;
            // no drift cell here (on the chamber edge or just outside)
            // this hit would otherwise be discarded downstream in the digitizer

            DTWireId wid(lid,wire);
            double thickness = det->surface().bounds().thickness();
            LocalVector lmom = det->toLocal(GlobalVector(crossing.direction(path.second)));
            lmom = lmom.unit()*propagatedState.localMomentum().mag();

            // Factor that takes into account the (rec)hits lost because of delta's, etc.:
            // (Not fully satisfactory patch, but it seems to work...)
            double pmu = lmom.mag();
            double theDTHitIneff = pmu>0? exp(kDT*log(pmu)+fDT):0.;
            if (random->flatShoot()<theDTHitIneff) continue;

            double eloss = 0;
            double pz = fabs(lmom.z());
            LocalPoint entry = lpos - 0.5*thickness*lmom/pz;
            LocalPoint exit = lpos + 0.5*thickness*lmom/pz;
            double dtof = path.second*rbeta;
            int trkid = mySimTrack.trackId();
            unsigned int id = wid.rawId();
            short unsigned int processType = 2;
            PSimHit hit(entry,exit,lmom.mag(),
                        tof+dtof,eloss,pid,id,trkid,lmom.theta(),lmom.phi(),processType);
            theDTHits.push_back(hit);

          }
        }
      }
      else if ( gd->subDetector() == GeomDetEnumerators::CSC ) {
        CSCDetId id(gd->geographicalId());
        const CSCChamber *chamber = cscGeom->chamber(id);
        std::vector<const CSCLayer *> layers = chamber->layers();
        for ( unsigned int ilayer=0; ilayer<layers.size(); ilayer++ ) {
          CSCDetId lid = layers[ilayer]->id();

#ifdef FAMOS_DEBUG
            std::cout << "    Extrapolated to CSC (" 
                      << lid.endcap() << "," 
                      << lid.ring() << "," 
                      << lid.station() << "," 
                      << lid.layer() << ")" << std::endl;
#endif

          const GeomDetUnit *det = cscGeom->idToDetUnit(lid);
          HelixArbitraryPlaneCrossing crossing(propagatedState.globalPosition().basicVector(),
                                               propagatedState.globalMomentum().basicVector(),
                                               propagatedState.transverseCurvature(),
                                               anyDirection);
          std::pair<bool,double> path = crossing.pathLength(det->surface());
          if ( ! path.first ) continue;
          LocalPoint lpos = det->toLocal(GlobalPoint(crossing.position(path.second)));
          // For CSCs the Bounds are for chamber frames not gas regions
          //      if ( ! det->surface().bounds().inside(lpos) ) continue;
          // New function knows where the 'active' volume is:
          const CSCLayerGeometry* laygeom = layers[ilayer]->geometry();
          if ( ! laygeom->inside( lpos ) ) continue; 
          //double thickness = laygeom->thickness(); gives number which is about 20 times too big
          double thickness = det->surface().bounds().thickness(); // this one works much better...
          LocalVector lmom = det->toLocal(GlobalVector(crossing.direction(path.second)));
          lmom = lmom.unit()*propagatedState.localMomentum().mag();
           
          // Factor that takes into account the (rec)hits lost because of delta's, etc.:
          // (Not fully satisfactory patch, but it seems to work...)
          double pmu = lmom.mag();
          double theCSCHitIneff = pmu>0? exp(kCSC*log(pmu)+fCSC):0.;
          // Take into account the different geometry in ME11:
          if (id.station()==1 && id.ring()==1)  theCSCHitIneff = theCSCHitIneff*0.442;
          if (random->flatShoot()<theCSCHitIneff) continue;

          double eloss = 0;
          double pz = fabs(lmom.z());
          LocalPoint entry = lpos - 0.5*thickness*lmom/pz;
          LocalPoint exit = lpos + 0.5*thickness*lmom/pz;
          double dtof = path.second*rbeta;
          int trkid = mySimTrack.trackId();
          unsigned int id = lid.rawId();
          short unsigned int processType = 2;
          PSimHit hit(entry,exit,lmom.mag(),
                      tof+dtof,eloss,pid,id,trkid,lmom.theta(),lmom.phi(),processType);
          theCSCHits.push_back(hit);
        }
      }
      else if ( gd->subDetector() == GeomDetEnumerators::RPCBarrel ||
                gd->subDetector() == GeomDetEnumerators::RPCEndcap ) {
        RPCDetId id(gd->geographicalId());
        const RPCChamber *chamber = rpcGeom->chamber(id);
        std::vector<const RPCRoll *> roll = chamber->rolls();
        for ( unsigned int iroll=0; iroll<roll.size(); iroll++ ) {
          RPCDetId rid = roll[iroll]->id();

#ifdef FAMOS_DEBUG
          std::cout << "    Extrapolated to RPC (" 
                    << rid.ring() << "," 
                    << rid.station() << ","
                    << rid.sector() << ","
                    << rid.subsector() << ","
                    << rid.layer() << ","
                    << rid.roll() << ")" << std::endl;
#endif

          const GeomDetUnit *det = rpcGeom->idToDetUnit(rid);
          HelixArbitraryPlaneCrossing crossing(propagatedState.globalPosition().basicVector(),
                                               propagatedState.globalMomentum().basicVector(),
                                               propagatedState.transverseCurvature(),
                                               anyDirection);
          std::pair<bool,double> path = crossing.pathLength(det->surface());
          if ( ! path.first ) continue;
          LocalPoint lpos = det->toLocal(GlobalPoint(crossing.position(path.second)));
          if ( ! det->surface().bounds().inside(lpos) ) continue; 
          double thickness = det->surface().bounds().thickness();
          LocalVector lmom = det->toLocal(GlobalVector(crossing.direction(path.second)));
          lmom = lmom.unit()*propagatedState.localMomentum().mag();
          double eloss = 0;
          double pz = fabs(lmom.z());
          LocalPoint entry = lpos - 0.5*thickness*lmom/pz;
          LocalPoint exit = lpos + 0.5*thickness*lmom/pz;
          double dtof = path.second*rbeta;
          int trkid = mySimTrack.trackId();
          unsigned int id = rid.rawId();
          short unsigned int processType = 2;
          PSimHit hit(entry,exit,lmom.mag(),
                      tof+dtof,eloss,pid,id,trkid,lmom.theta(),lmom.phi(),processType);
          theRPCHits.push_back(hit);
        }
      }
      else {
        std::cout << "Extrapolated to unknown subdetector '" << gd->subDetector() << "'..." << std::endl;
      }
    }
  }
  }

  std::auto_ptr<edm::PSimHitContainer> pcsc(new edm::PSimHitContainer);
  int n = 0;
  for ( std::vector<PSimHit>::const_iterator i = theCSCHits.begin();
        i != theCSCHits.end(); i++ ) {
    pcsc->push_back(*i);
    n += 1;
  }
  iEvent.put(pcsc,"MuonCSCHits");

  std::auto_ptr<edm::PSimHitContainer> pdt(new edm::PSimHitContainer);
  n = 0;
  for ( std::vector<PSimHit>::const_iterator i = theDTHits.begin();
        i != theDTHits.end(); i++ ) {
    pdt->push_back(*i);
    n += 1;
  }
  iEvent.put(pdt,"MuonDTHits");

  std::auto_ptr<edm::PSimHitContainer> prpc(new edm::PSimHitContainer);
  n = 0;
  for ( std::vector<PSimHit>::const_iterator i = theRPCHits.begin();
        i != theRPCHits.end(); i++ ) {
    prpc->push_back(*i);
    n += 1;
  }
  iEvent.put(prpc,"MuonRPCHits");

}


// ------------ method called once each job just after ending the event loop  ------------
void 
MuonSimHitProducer::endJob() 
{
}


void 
MuonSimHitProducer::readParameters(const edm::ParameterSet& fastMuons, 
                                   const edm::ParameterSet& fastTracks,
                                   const edm::ParameterSet& matEff) {
  // Muons
  theSimModuleLabel_   = fastMuons.getParameter<std::string>("simModuleLabel");
  theSimModuleProcess_ = fastMuons.getParameter<std::string>("simModuleProcess");
  theTrkModuleLabel_   = fastMuons.getParameter<std::string>("trackModuleLabel");
  std::vector<double> simHitIneffDT  = fastMuons.getParameter<std::vector<double> >("simHitDTIneffParameters");
  std::vector<double> simHitIneffCSC = fastMuons.getParameter<std::vector<double> >("simHitCSCIneffParameters");
  kDT = simHitIneffDT[0];
  fDT = simHitIneffDT[1];
  kCSC = simHitIneffCSC[0];
  fCSC = simHitIneffCSC[1];  

  // Tracks
  fullPattern_  = fastTracks.getUntrackedParameter<bool>("FullPatternRecognition");

  // The following should be on LogInfo
  //  std::cout << " MUON SIM HITS: FastSimulation parameters " << std::endl;
  //  std::cout << " ============================================== " << std::endl;
  //  if ( fullPattern_ ) 
  //    std::cout << " The FULL pattern recognition option is turned ON" << std::endl;
  //  else
  //    std::cout << " The FAST tracking option is turned ON" << std::endl;

  // Material Effects
  theMaterialEffects = 0;
  if ( matEff.getParameter<bool>("PairProduction") || 
       matEff.getParameter<bool>("Bremsstrahlung") ||
       matEff.getParameter<bool>("EnergyLoss") || 
       matEff.getParameter<bool>("MultipleScattering") )
    theMaterialEffects = new MaterialEffects(matEff,random);

}

void    
MuonSimHitProducer::applyMaterialEffects(TrajectoryStateOnSurface& tsosWithdEdx,
                                         TrajectoryStateOnSurface& tsos,
                                         double radPath) { 

  // The energy loss simulator
  EnergyLossSimulator* energyLoss = theMaterialEffects->energyLossSimulator();

  // The multiple scattering simulator
  MultipleScatteringSimulator* multipleScattering = theMaterialEffects->multipleScatteringSimulator();

  // Initialize the Particle position, momentum and energy
  const Surface& nextSurface = tsos.surface();
  GlobalPoint gPos = energyLoss ? tsos.globalPosition() : tsosWithdEdx.globalPosition();
  GlobalVector gMom = energyLoss ? tsos.globalMomentum() : tsosWithdEdx.globalMomentum();  
  double mu = 0.1056583692;
  double en = std::sqrt(gMom.mag2()+mu*mu);

  // And now create the Particle
  XYZTLorentzVector position(gPos.x(),gPos.y(),gPos.z(),0.);
  XYZTLorentzVector momentum(gMom.x(),gMom.y(),gMom.z(),en);
  float charge = (float)(tsos.charge());
  ParticlePropagator theMuon(momentum,position,charge,0);
  theMuon.setID(-(int)charge*13);

  // Recompute the energy loss to get the fluctuations
  if ( energyLoss ) { 
    // Difference between with and without dE/dx (average only)
    // (for corrections once fluctuations are applied)
    GlobalPoint gPosWithdEdx = tsosWithdEdx.globalPosition();
    GlobalVector gMomWithdEdx = tsosWithdEdx.globalMomentum();
    double enWithdEdx = std::sqrt(gMomWithdEdx.mag2()+mu*mu);
    XYZTLorentzVector 
      deltaPos(gPosWithdEdx.x()-gPos.x(),gPosWithdEdx.y()-gPos.y(),
               gPosWithdEdx.z()-gPos.z(),0.);
    XYZTLorentzVector 
      deltaMom(gMomWithdEdx.x()-gMom.x(),gMomWithdEdx.y()-gMom.y(),
               gMomWithdEdx.z()-gMom.z(), enWithdEdx      -en);

    // Energy loss in iron (+ fluctuations)
    energyLoss->updateState(theMuon,radPath);

    // Correcting factors to account for slight differences in material descriptions
    // (Material description is more accurate in the stepping helix propagator)
    radPath *= -deltaMom.E()/energyLoss->mostLikelyLoss();
    double fac = energyLoss->deltaMom().E()/energyLoss->mostLikelyLoss();

    // Particle momentum & position after energy loss + fluctuation
    XYZTLorentzVector theNewMomentum = theMuon.momentum() + energyLoss->deltaMom() + fac * deltaMom;
    XYZTLorentzVector theNewPosition = theMuon.vertex() + fac * deltaPos;
    fac  = (theNewMomentum.E()*theNewMomentum.E()-mu*mu)/theNewMomentum.Vect().Mag2();
    fac  = fac>0.? std::sqrt(fac) : 1E-9;
    theMuon.SetXYZT(theNewMomentum.Px()*fac,theNewMomentum.Py()*fac,
                    theNewMomentum.Pz()*fac,theNewMomentum.E());    
    theMuon.setVertex(theNewPosition);

  }

  // Does the actual mutliple scattering
  if ( multipleScattering ) {
    // Pass the vector normal to the "next" surface 
    GlobalVector normal = nextSurface.tangentPlane(tsos.globalPosition())->normalVector();
    multipleScattering->setNormalVector(normal);
    // Compute the amount of multiple scattering after a given path length
    multipleScattering->updateState(theMuon,radPath);
  }
  
  // Fill the propagated state
  GlobalPoint propagatedPosition(theMuon.X(),theMuon.Y(),theMuon.Z());
  GlobalVector propagatedMomentum(theMuon.Px(),theMuon.Py(),theMuon.Pz());
  GlobalTrajectoryParameters propagatedGtp(propagatedPosition,propagatedMomentum,(int)charge,magfield);
  tsosWithdEdx = TrajectoryStateOnSurface(propagatedGtp,nextSurface);

}



//define this as a plug-in
DEFINE_FWK_MODULE(MuonSimHitProducer);