Py8JetGun.cc

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#include <memory>

#include "GeneratorInterface/Core/interface/GeneratorFilter.h"
#include "GeneratorInterface/ExternalDecays/interface/ExternalDecayDriver.h"

#include "GeneratorInterface/Pythia8Interface/interface/Py8GunBase.h"

namespace gen {

  class Py8JetGun : public Py8GunBase {
  public:
    Py8JetGun(edm::ParameterSet const&);
    ~Py8JetGun() override {}

    bool generatePartonsAndHadronize() override;
    const char* classname() const override;

  private:
    // PtGun particle(s) characteristics
    double fMinEta;
    double fMaxEta;
    double fMinP;
    double fMaxP;
    double fMinE;
    double fMaxE;
  };

  // implementation
  //
  Py8JetGun::Py8JetGun(edm::ParameterSet const& ps) : Py8GunBase(ps) {
    // ParameterSet defpset ;
    edm::ParameterSet pgun_params = ps.getParameter<edm::ParameterSet>("PGunParameters");  // , defpset ) ;
    fMinEta = pgun_params.getParameter<double>("MinEta");                                  // ,-2.2);
    fMaxEta = pgun_params.getParameter<double>("MaxEta");                                  // , 2.2);
    fMinP = pgun_params.getParameter<double>("MinP");                                      // ,  0.);
    fMaxP = pgun_params.getParameter<double>("MaxP");                                      // ,  0.);
    fMinE = pgun_params.getParameter<double>("MinE");                                      // ,  0.);
    fMaxE = pgun_params.getParameter<double>("MaxE");                                      // ,  0.);
  }

  bool Py8JetGun::generatePartonsAndHadronize() {
    fMasterGen->event.reset();

    int NTotParticles = fPartIDs.size();

    // energy below is dummy, it is not used
    (fMasterGen->event).append(990, -11, 0, 0, 2, 1 + NTotParticles, 0, 0, 0., 0., 0., 15000., 15000.);

    double totPx = 0.;
    double totPy = 0.;
    double totPz = 0.;
    double totE = 0.;
    double totM = 0.;
    double phi, eta, the, ee, pp;

    for (size_t i = 0; i < fPartIDs.size(); i++) {
      int particleID = fPartIDs[i];  // this is PDG

      phi = 2. * M_PI * randomEngine().flat();
      the = acos(-1. + 2. * randomEngine().flat());

      // from input
      //
      ee = (fMaxE - fMinE) * randomEngine().flat() + fMinE;

      double mass = (fMasterGen->particleData).m0(particleID);

      pp = sqrt(ee * ee - mass * mass);

      double px = pp * sin(the) * cos(phi);
      double py = pp * sin(the) * sin(phi);
      double pz = pp * cos(the);

      if (!((fMasterGen->particleData).isParticle(particleID))) {
        particleID = std::fabs(particleID);
      }
      (fMasterGen->event).append(particleID, 1, 1, 0, 0, 0, 0, 0, px, py, pz, ee, mass);
      int eventSize = (fMasterGen->event).size() - 1;
      // -log(flat) = exponential distribution
      double tauTmp = -(fMasterGen->event)[eventSize].tau0() * log(randomEngine().flat());
      (fMasterGen->event)[eventSize].tau(tauTmp);

      // values for computing total mass
      //
      totPx += px;
      totPy += py;
      totPz += pz;
      totE += ee;
    }

    totM = sqrt(totE * totE - (totPx * totPx + totPy * totPy + totPz * totPz));

    //now the boost (from input params)
    //
    pp = (fMaxP - fMinP) * randomEngine().flat() + fMinP;
    ee = sqrt(totM * totM + pp * pp);

    //the boost direction (from input params)
    //
    phi = (fMaxPhi - fMinPhi) * randomEngine().flat() + fMinPhi;
    eta = (fMaxEta - fMinEta) * randomEngine().flat() + fMinEta;
    the = 2. * atan(exp(-eta));

    double betaX = pp / ee * std::sin(the) * std::cos(phi);
    double betaY = pp / ee * std::sin(the) * std::sin(phi);
    double betaZ = pp / ee * std::cos(the);

    // boost all particles
    //
    (fMasterGen->event).bst(betaX, betaY, betaZ);

    if (!fMasterGen->next())
      return false;

    event() = std::make_unique<HepMC::GenEvent>();
    return toHepMC.fill_next_event(fMasterGen->event, event().get());
  }

  const char* Py8JetGun::classname() const { return "Py8JetGun"; }

  typedef edm::GeneratorFilter<gen::Py8JetGun, gen::ExternalDecayDriver> Pythia8JetGun;

}  // namespace gen

using gen::Pythia8JetGun;
DEFINE_FWK_MODULE(Pythia8JetGun);