GeneratorInterface/ExhumeInterface/plugins/DiPhoton.cpp - master - githubmirror/cmssw

GeneratorInterface/ExhumeInterface/plugins/DiPhoton.cpp

49 строк2 KB

Matti Kortelainen

Move contents of ExhumeHadronizer.{h,cc} to ExhumeGeneratorFilter

16 мар 2026, 11:45

16 мар 2026, 11:45c901e15

//-*-c++-*-
//-*-DiPhoton.cpp-*-ahamil@localhost
//   Written by James Monk and Andrew Pilkington
////////////////////////////////////////////////////////////////////////////////

#include "DiPhoton.h"

////////////////////////////////////////////////////////////////////////////////
Exhume::DiPhoton::DiPhoton(const edm::ParameterSet& pset) : TwoSpace(pset) {
  std::cout << std::endl << "   =DiPhoton production selected=" << std::endl << std::endl;
  Partons[0].id = 22;
  Partons[1].id = 22;
  Partons[0].Colour = 0;
  Partons[0].AntiColour = 0;
  Partons[1].Colour = 0;
  Partons[1].AntiColour = 0;
  Inv64PI2 = double(1.0) / (64.0 * M_PI * M_PI);
  PI2 = M_PI * M_PI;

  Nup = 2;
  Ndown = 2;
  MatFact = 4.0 * (2 * double(16.0) / 81 + 2 * double(1.0) / 81) * Inv64PI2;

  Name = "di-photon";
  SetThetaMin(acos(0.95));
}
////////////////////////////////////////////////////////////////////////////////
double Exhume::DiPhoton::MatrixElement() {
  //M++++ + M--++ can interfere because of same final states
  double _Sigma = -0.5 * (0.5 * (1 + CosTheta * CosTheta)) *
                      (log((1.0 - CosTheta) / (1.0 + CosTheta)) * log((1.0 - CosTheta) / (1.0 + CosTheta)) + PI2) -
                  CosTheta * log((1.0 - CosTheta) / (1.0 + CosTheta));

  //Total M^2 = 2* above (helicity opposites) plus 2*(M+++- + M--+-)
  // note M+++- = M++-+ = 1 (same for helicity opposites
  return (2 * _Sigma * _Sigma + 8.0);
}
////////////////////////////////////////////////////////////////////////////////

double Exhume::DiPhoton::SubProcess() {
  double m_elem_sq = MatrixElement();
  double _Sigma = MatFact * (m_elem_sq) / sHat;
  _Sigma = _Sigma * AlphaS(SqrtsHat / 2) * AlphaS(SqrtsHat / 2) * AlphaEw * AlphaEw;
  return (Gev2fb * _Sigma);
}

void Exhume::DiPhoton::LIPS2Amp() { return; }

void Exhume::DiPhoton::Amp2LIPS() { return; }