GEMDigitizer/src/GEMSignalModel.cc

0001 #include "SimMuon/GEMDigitizer/interface/GEMSignalModel.h"
0002 #include "Geometry/GEMGeometry/interface/GEMEtaPartitionSpecs.h"
0003 #include "Geometry/CommonTopologies/interface/GEMStripTopology.h"
0004 #include "Geometry/GEMGeometry/interface/GEMGeometry.h"
0005 #include "FWCore/MessageLogger/interface/MessageLogger.h"
0006 #include "FWCore/Utilities/interface/Exception.h"
0007 #include "CLHEP/Random/RandFlat.h"
0008 #include "CLHEP/Random/RandPoissonQ.h"
0009 #include "CLHEP/Random/RandGaussQ.h"
0010 #include "CLHEP/Units/GlobalPhysicalConstants.h"
0011 #include "DataFormats/Math/interface/GeantUnits.h"
0012 #include <cmath>
0013 #include <utility>
0014 #include <map>
0015
0016 GEMSignalModel::GEMSignalModel(const edm::ParameterSet& config)
0017     : GEMDigiModel(config),
0018       averageEfficiency_(config.getParameter<double>("averageEfficiency")),
0019       averageShapingTime_(config.getParameter<double>("averageShapingTime")),
0020       timeResolution_(config.getParameter<double>("timeResolution")),
0021       timeJitter_(config.getParameter<double>("timeJitter")),
0022       signalPropagationSpeed_(config.getParameter<double>("signalPropagationSpeed")),
0023       resolutionX_(config.getParameter<double>("resolutionX")),
0024       cspeed(geant_units::operators::convertMmToCm(CLHEP::c_light)),
0025       // average energy required to remove an electron due to ionization for an Ar/CO2 gas mixture (in the ratio of 70/30) is 28.1 eV
0026       energyMinCut(28.1e-09) {}
0027
0028 GEMSignalModel::~GEMSignalModel() {}
0029
0030 void GEMSignalModel::simulate(const GEMEtaPartition* roll,
0031                               const edm::PSimHitContainer& simHits,
0032                               CLHEP::HepRandomEngine* engine,
0033                               Strips& strips_,
0034                               DetectorHitMap& detectorHitMap_) {
0035   const GEMStripTopology* top(dynamic_cast<const GEMStripTopology*>(&(roll->topology())));
0036   for (const auto& hit : simHits) {
0037     if (hit.energyLoss() < energyMinCut)
0038       continue;
0039     const int bx(getSimHitBx(&hit, engine));
0040     const std::vector<std::pair<int, int> >& cluster(simulateClustering(top, &hit, bx, engine));
0041     for (const auto& digi : cluster) {
0042       detectorHitMap_.emplace(digi, &hit);
0043       strips_.emplace(digi);
0044     }
0045   }
0046 }
0047
0048 int GEMSignalModel::getSimHitBx(const PSimHit* simhit, CLHEP::HepRandomEngine* engine) {
0049   int bx = -999;
0050   const LocalPoint simHitPos(simhit->localPosition());
0051   const float tof(simhit->timeOfFlight());
0052   // random Gaussian time correction due to electronics jitter
0053   float randomJitterTime = CLHEP::RandGaussQ::shoot(engine, 0., timeJitter_);
0054   const GEMDetId id(simhit->detUnitId());
0055   const GEMEtaPartition* roll(geometry_->etaPartition(id));
0056   if (!roll) {
0057     throw cms::Exception("Geometry") << "GEMSignalModel::getSimHitBx() - GEM simhit id does not match any GEM roll id: "
0058                                      << id << "\n";
0059     return 999;
0060   }
0061   if (roll->id().region() == 0) {
0062     throw cms::Exception("Geometry")
0063         << "GEMSignalModel::getSimHitBx() - this GEM id is from barrel, which cannot happen: " << roll->id() << "\n";
0064   }
0065   const int nstrips = roll->nstrips();
0066   float middleStrip = nstrips / 2.;
0067   const LocalPoint& middleOfRoll = roll->centreOfStrip(middleStrip);
0068   const GlobalPoint& globMiddleRol = roll->toGlobal(middleOfRoll);
0069   double muRadius = sqrt(globMiddleRol.x() * globMiddleRol.x() + globMiddleRol.y() * globMiddleRol.y() +
0070                          globMiddleRol.z() * globMiddleRol.z());
0071   double timeCalibrationOffset_ = muRadius / cspeed;  //[ns]
0072
0073   const GEMStripTopology* top(dynamic_cast<const GEMStripTopology*>(&(roll->topology())));
0074   const float halfStripLength(0.5 * top->stripLength());
0075   const float distanceFromEdge(halfStripLength - simHitPos.y());
0076
0077   // signal propagation speed in material in [cm/ns]
0078   double signalPropagationSpeedTrue = signalPropagationSpeed_ * cspeed;
0079
0080   // average time for the signal to propagate from the SimHit to the top of a strip
0081   const float averagePropagationTime(distanceFromEdge / signalPropagationSpeedTrue);
0082   // random Gaussian time correction due to the finite timing resolution of the detector
0083   float randomResolutionTime = CLHEP::RandGaussQ::shoot(engine, 0., timeResolution_);
0084   const float simhitTime(tof + averageShapingTime_ + randomResolutionTime + averagePropagationTime + randomJitterTime);
0085   float referenceTime = 0.;
0086   referenceTime = timeCalibrationOffset_ + halfStripLength / signalPropagationSpeedTrue + averageShapingTime_;
0087   const float timeDifference(simhitTime - referenceTime);
0088   // assign the bunch crossing
0089   bx = static_cast<int>(std::round((timeDifference) / 25.));
0090
0091   // check time
0092   LogDebug("GEMDigiProducer") << "checktime "
0093                               << "bx = " << bx << "\tdeltaT = " << timeDifference << "\tsimT =  " << simhitTime
0094                               << "\trefT =  " << referenceTime << "\ttof = " << tof
0095                               << "\tavePropT =  " << averagePropagationTime
0096                               << "\taveRefPropT = " << halfStripLength / signalPropagationSpeedTrue << "\n";
0097   return bx;
0098 }
0099
0100 std::vector<std::pair<int, int> > GEMSignalModel::simulateClustering(const GEMStripTopology* top,
0101                                                                      const PSimHit* simHit,
0102                                                                      const int bx,
0103                                                                      CLHEP::HepRandomEngine* engine) {
0104   const LocalPoint& hit_entry(simHit->entryPoint());
0105   const LocalPoint& hit_exit(simHit->exitPoint());
0106
0107   LocalPoint start_point, end_point;
0108   if (hit_entry.x() < hit_exit.x()) {
0109     start_point = hit_entry;
0110     end_point = hit_exit;
0111   } else {
0112     start_point = hit_exit;
0113     end_point = hit_entry;
0114   }
0115
0116   // Add Gaussian noise to the points towards outside.
0117   float smeared_start_x = start_point.x() - std::abs(CLHEP::RandGaussQ::shoot(engine, 0, resolutionX_));
0118   float smeared_end_x = end_point.x() + std::abs(CLHEP::RandGaussQ::shoot(engine, 0, resolutionX_));
0119
0120   LocalPoint smeared_start_point(smeared_start_x, start_point.y(), start_point.z());
0121   LocalPoint smeared_end_point(smeared_end_x, end_point.y(), end_point.z());
0122
0123   int cluster_start = top->channel(smeared_start_point);
0124   int cluster_end = top->channel(smeared_end_point);
0125
0126   std::vector<std::pair<int, int> > cluster;
0127   for (int strip = cluster_start; strip <= cluster_end; strip++) {
0128     cluster.emplace_back(strip, bx);
0129   }
0130
0131   return cluster;
0132 }