simcore::g4user::PrimaryGeneratorAction Class Reference

Implementation of Geant4 primary generator action. More...

#include <PrimaryGeneratorAction.h>

Public Member Functions
	PrimaryGeneratorAction (const framework::config::Parameters &parameters)
virtual	~PrimaryGeneratorAction ()=default
	Class destructor.
void	GeneratePrimaries (G4Event *event) override
	Generate primaries for the event.

Private Attributes
bool	useBeamspot_ {false}
	Flag denoting whether the vertex position of a particle should be smeared.
double	beamspotXSize_ {0}
	Extent of the beamspot in x.
double	beamspotYSize_ {0}
	Extent of the beamspot in y.
double	beamspotZSize_ {0.}
	Extent of the beamspot in y.
bool	time_shift_primaries_ {true}
	Should we time-shift so that the primary vertices arrive (or originate) at t=0ns at z=0mm?

Detailed Description

Implementation of Geant4 primary generator action.

Definition at line 35 of file PrimaryGeneratorAction.h.

Constructor & Destructor Documentation

PrimaryGeneratorAction()

simcore::g4user::PrimaryGeneratorAction::PrimaryGeneratorAction

(

const framework::config::Parameters &

parameters

)

Definition at line 29 of file PrimaryGeneratorAction.cxx.

    : G4VUserPrimaryGeneratorAction() {
  // Check whether a beamspot should be used or not.
  auto beamSpot{
      parameters.getParameter<std::vector<double> >("beamSpotSmear", {})};
  if (!beamSpot.empty()) {
    useBeamspot_ = true;
    beamspotXSize_ = beamSpot[0];
    beamspotYSize_ = beamSpot[1];
    beamspotZSize_ = beamSpot[2];
  }
 
  time_shift_primaries_ = parameters.getParameter<bool>("time_shift_primaries");
 
  auto generators{
      parameters.getParameter<std::vector<framework::config::Parameters> >(
          "generators", {})};
  if (generators.empty()) {
    EXCEPTION_RAISE("MissingGenerator",
                    "Need to define some generator of primaries.");
  }
 
  for (auto& generator : generators) {
    PrimaryGenerator::Factory::get().make(
        generator.getParameter<std::string>("class_name"),
        generator.getParameter<std::string>("instance_name"), generator);
  }
}

Member Function Documentation

GeneratePrimaries()

void simcore::g4user::PrimaryGeneratorAction::GeneratePrimaries ( G4Event *  event )

override

Generate primaries for the event.

This is called by the RunManager before being given to the EventManager to process. This means we must create the UserEventInformation here so that it is accessible for including the weights imported by the primary generators.

See also

G4RunManager::GenerateEvent for where this method is called

G4RunManager::ProcessOneEvent for where G4RunManager::GenerateEvent is called

Set UserInformation for primary vertices if they haven't been set before.

Some features downstream of the primaries require certain user info to function properly. This ensures that it happens.

Makes sure that each particle on each primary vertex has

1. A defined UserPrimaryParticleInformation member
2. The HepEvtStatus for this primary info is non-zero

If we are passed configuration to smear the beam spot, we smear the beam spot around the spot generated by the primary generator.

If we are configured to time-shift the primaries, we shift them so that t=0 coincides with primaries arriving at (or coming from) the target.

Parameters

event

The Geant4 event.

Definition at line 59 of file PrimaryGeneratorAction.cxx.

                                                             {
  /*
   * Create our Event information first so that it
   * can be accessed by everyone from now on.
   */
  // Make sure we aren't overwriting a different information container
  if (event->GetUserInformation()) {
    EXCEPTION_RAISE(
        "Misconfig",
        "There was a UserEventInformation attached before beginning event."
        "\nI don't know how this happend!!");
  }
 
  // Make our information container and give it to geant4
  //    G4Event owns the event information and will delete it
  auto event_info = new UserEventInformation;
  event->SetUserInformation(event_info);
 
  PrimaryGenerator::Factory::get().apply([event](const auto& generator) {
    generator->GeneratePrimaryVertex(event);
  });
 
  // smear all primary vertices (if activated)
  int nPV = event->GetNumberOfPrimaryVertex();
  if (nPV > 0) {
    // loop over all vertices generated
    for (int iPV = 0; iPV < nPV; ++iPV) {
      G4PrimaryVertex* primary_vertex = event->GetPrimaryVertex(iPV);
 
      // Loop over all particle associated with the primary vertex and
      // set the generator status to 1.
      for (int iparticle = 0; iparticle < primary_vertex->GetNumberOfParticle();
           ++iparticle) {
        G4PrimaryParticle* primary = primary_vertex->GetPrimary(iparticle);
 
        auto primary_info{dynamic_cast<UserPrimaryParticleInformation*>(
            primary->GetUserInformation())};
        if (not primary_info) {
          // no user info defined
          //  ==> make a new one
          primary_info = new UserPrimaryParticleInformation;
          primary->SetUserInformation(primary_info);
        }  // check if primaryinfo is defined
 
        int hepStatus = primary_info->getHepEvtStatus();
        if (hepStatus <= 0) {
          // undefined hepStatus ==> set to 1
          primary_info->setHepEvtStatus(1);
        }  // check if hepStatus defined
 
      }  // iparticle - loop over primary particles from this vertex
 
      // include the weight of this primary vertex in the event weight
      event_info->incWeight(primary_vertex->GetWeight());
 
      // smear beamspot if it is turned on
      if (useBeamspot_) {
        double x0_i = primary_vertex->GetX0();
        double y0_i = primary_vertex->GetY0();
        double z0_i = primary_vertex->GetZ0();
        /*
         * G4UniformRand returns a number in [0,1]
         *  - we shift this range so that it is [-0.5,0.5]
         *  - multiply by the width to get [-0.5*size,0.5*size]
         *  - add the initial point (in case its off center) to get
         *    [init-0.5*size, init+0.5*size]
         */
        double x0_f = beamspotXSize_ * (G4UniformRand() - 0.5) + x0_i;
        double y0_f = beamspotYSize_ * (G4UniformRand() - 0.5) + y0_i;
        double z0_f = beamspotZSize_ * (G4UniformRand() - 0.5) + z0_i;
        primary_vertex->SetPosition(x0_f, y0_f, z0_f);
      }
 
      // shift so that t=0 coincides with primaries arriving at (or coming from)
      // the target
      if (time_shift_primaries_) {
        primary_vertex->SetT0(primary_vertex->GetT0() +
                              primary_vertex->GetZ0() / 299.702547);
      }
 
    }  // iPV - loop over primary vertices
  } else {
    EXCEPTION_RAISE(
        "NoPrimaries",
        "No primary vertices were produced by any of the generators.");
  }
}

References simcore::UserPrimaryParticleInformation::getHepEvtStatus().

Member Data Documentation

beamspotXSize_

double simcore::g4user::PrimaryGeneratorAction::beamspotXSize_ {0}

private

Extent of the beamspot in x.

Definition at line 91 of file PrimaryGeneratorAction.h.

{0};

beamspotYSize_

double simcore::g4user::PrimaryGeneratorAction::beamspotYSize_ {0}

private

Extent of the beamspot in y.

Definition at line 94 of file PrimaryGeneratorAction.h.

{0};

beamspotZSize_

double simcore::g4user::PrimaryGeneratorAction::beamspotZSize_ {0.}

private

Extent of the beamspot in y.

Definition at line 97 of file PrimaryGeneratorAction.h.

{0.};

time_shift_primaries_

bool simcore::g4user::PrimaryGeneratorAction::time_shift_primaries_ {true}

private

Should we time-shift so that the primary vertices arrive (or originate) at t=0ns at z=0mm?

Note

This should remain true unless the user knows what they are doing!

Definition at line 105 of file PrimaryGeneratorAction.h.

{true};

useBeamspot_

bool simcore::g4user::PrimaryGeneratorAction::useBeamspot_ {false}

private

Flag denoting whether the vertex position of a particle should be smeared.

Definition at line 88 of file PrimaryGeneratorAction.h.

{false};

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The documentation for this class was generated from the following files:

• SimCore/include/SimCore/G4User/PrimaryGeneratorAction.h
• SimCore/src/SimCore/G4User/PrimaryGeneratorAction.cxx