MdtSensitiveDetector.cxx

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/*
  Copyright (C) 2002-2026 CERN for the benefit of the ATLAS collaboration
*/
 
#include "MuonSensitiveDetectorsR4/Utils.h"
 
#include "MdtSensitiveDetector.h"
 
#include <GeneratorObjects/HepMcParticleLink.h>
 
#include <limits>
#include <iostream>
#include <GeoPrimitives/CLHEPtoEigenConverter.h>
#include <GeoModelKernel/throwExcept.h>
#include <GaudiKernel/SystemOfUnits.h>
 
using namespace MuonGMR4;
using namespace CxxUtils;
using namespace ActsTrk;
namespace MuonG4R4{
 
const MuonGMR4::MdtReadoutElement* MdtSensitiveDetector::getReadoutElement(const G4TouchableHistory* touchHist) const {
   const std::string stationVolume = touchHist->GetVolume(2)->GetName();
   using namespace MuonGMR4;
   const std::vector<std::string> volumeTokens = tokenize(stationVolume, "_");
   ATH_MSG_VERBOSE("Name of the station volume is "<<stationVolume);
   if (volumeTokens.size() != 5) {
      THROW_EXCEPTION(" Cannot deduce the station name from "<<stationVolume);
   }
   const std::string stName = volumeTokens[0].substr(0,3);
   const int stationEta = atoi(volumeTokens[2]);
   const int stationPhi = atoi(volumeTokens[3]);
   const int multiLayer = atoi(volumeTokens[4]);
   const MdtIdHelper& idHelper{m_detMgr->idHelperSvc()->mdtIdHelper()};
   const Identifier detElId = idHelper.multilayerID(idHelper.elementID(stName,stationEta, stationPhi), multiLayer);
   const MdtReadoutElement* readOutEle = m_detMgr->getMdtReadoutElement(detElId);
   if (!readOutEle) {
      THROW_EXCEPTION(" Failed to retrieve a valid detector element from "
                     <<m_detMgr->idHelperSvc()->toStringDetEl(detElId)<<" "<<stationVolume);
   }
   return readOutEle;
}
 
G4bool MdtSensitiveDetector::ProcessHits(G4Step* aStep,G4TouchableHistory* /*ROHist*/) {

    if (!processStep(aStep)) {
      return true;
    }
    G4Track* currentTrack = aStep->GetTrack();
    const G4StepPoint* preStep = aStep->GetPreStepPoint();
    const G4TouchableHistory* touchHist = static_cast<const G4TouchableHistory*>(preStep->GetTouchable());
    const MdtReadoutElement* reEle{getReadoutElement(touchHist)};
 
    const ActsTrk::GeometryContext gctx{getGeoContext()};
 
    const Identifier HitID = getIdentifier(gctx, reEle, touchHist);
    if (!HitID.is_valid()) {
        ATH_MSG_VERBOSE("No valid hit found");
        return true;
    }
 
    const Amg::Transform3D globalToLocal{reEle->globalToLocalTransform(gctx, reEle->measurementHash(HitID))};
 
    // transform pre and post step positions to local positions
    const Amg::Vector3D prePosition{Amg::Hep3VectorToEigen(preStep->GetPosition())};
    const Amg::Vector3D postPosition{Amg::Hep3VectorToEigen(aStep->GetPostStepPoint()->GetPosition())};
    
    const Amg::Vector3D trackDirection{(postPosition - prePosition).unit()};
 
    const Amg::Vector3D trackLocPos{globalToLocal * prePosition};  
    const Amg::Vector3D trackLocDir{globalToLocal.linear()* trackDirection};
  
    double lambda = Amg::intersect<3>(Amg::Vector3D::Zero(), Amg::Vector3D::UnitZ(),
                                      trackLocPos, trackLocDir).value_or(0);
    if (std::abs(currentTrack->GetDefinition()->GetPDGEncoding()) == 11) {
        lambda = std::clamp(lambda, 0., aStep->GetStepLength());
    }
    const Amg::Vector3D driftHit{trackLocPos + lambda * trackLocDir};
 
 
    const double globalTime{preStep->GetGlobalTime() +  lambda / currentTrack->GetVelocity()};
 
    if (std::abs(currentTrack->GetDefinition()->GetPDGEncoding()) == 11) {
        const xAOD::MuonSimHit* lastRecord = lastSnapShot(HitID, aStep);
        if (lastRecord && lastRecord->localPosition().perp() < driftHit.perp()) {
            return true;
        }
    }
  
    ATH_MSG_VERBOSE(" Dumping of hit "<<m_detMgr->idHelperSvc()->toString(HitID)
                  <<", barcode: "<<genParticleLink(currentTrack).barcode()
                  <<", "<<(*currentTrack) <<", driftCircle: "<<Amg::toString(driftHit, 4)
                  <<", direction "<<Amg::toString(trackLocDir, 4) <<" to SimHit container ahead. ");
    saveHit(HitID, driftHit, trackLocDir, globalTime, aStep);
    return true;
}
Identifier MdtSensitiveDetector::getIdentifier(const ActsTrk::GeometryContext& gctx,
                                               const MuonGMR4::MdtReadoutElement* readOutEle,
                                               const G4TouchableHistory* touchHist) const {
   const Amg::Transform3D localToGlobal{getTransform(touchHist, 0)};
   Amg::Vector3D refTubePos = (readOutEle->globalToLocalTransform(gctx, readOutEle->measurementHash(1,1)) * localToGlobal).translation();
   ATH_MSG_VERBOSE("Position of the tube wire w.r.t. the first tube in the multi layer "<<Amg::toString(refTubePos, 2));
   static const double layerPitch = 1./ std::sin(60*Gaudi::Units::deg);
   const int layer = std::round(refTubePos.x() * layerPitch / readOutEle->tubePitch()) +1;
   if (layer <= 0) {
      THROW_EXCEPTION("Tube hit in nirvana -- It seems that the tube position "
                      <<Amg::toString(refTubePos, 2)<<", perp: "<<refTubePos.perp()
                      <<" is outside of the volume envelope "
                      <<m_detMgr->idHelperSvc()->toStringDetEl(readOutEle->identify())<<". ");      
   }
   refTubePos  = (readOutEle->globalToLocalTransform(gctx, readOutEle->measurementHash(layer,1)) * localToGlobal).translation();
   const double tubePitches = refTubePos.y() / readOutEle->tubePitch();
   unsigned int tube = std::round(tubePitches) + 1;
   tube = std::max(1u, std::min(readOutEle->numTubesInLay(), tube));
  const Amg::Transform3D closureCheck{readOutEle->globalToLocalTransform(gctx, 
                                      readOutEle->measurementHash(layer, tube))*localToGlobal};
    if (!Amg::isIdentity(closureCheck)) {
        ATH_MSG_WARNING("Correction needed "<<layer<<","<<tube<<" "<<Amg::toString(closureCheck));
        if (closureCheck.translation().y() > 0) ++tube;
        else --tube;
    }
   
   const IdentifierHash tubeHash = readOutEle->measurementHash(layer, tube);
   const Identifier tubeId = readOutEle->measurementId(tubeHash);
   {
        const Amg::Transform3D closureCheck{readOutEle->globalToLocalTransform(gctx, tubeHash)*localToGlobal};
        if (!Amg::isIdentity(closureCheck)) {
            THROW_EXCEPTION("Tube hit in Nirvana --  It seems that the tube position "
                             <<Amg::toString(refTubePos, 2)<<", perp: "<<refTubePos.perp()
                             <<" is outside of the volume envelope "
                             <<m_detMgr->idHelperSvc()->toStringDetEl(readOutEle->identify())<<". "
                             <<"Layer: "<<layer<<", tube: "<<tube<<" "
                             <<Amg::toString(closureCheck)
                             <<"tube volume : "<<touchHist->GetVolume(0)->GetName()
                             <<" mdt chamber: "<<touchHist->GetVolume(2)->GetName());    
        }
   }
   ATH_MSG_VERBOSE("Tube & layer number candidate "<<tube<<", "<<layer<<" back and forth transformation "
                     <<Amg::toString(closureCheck));
   return tubeId;  
}
 
}