StrangeDensity.cc

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#include "GeneratorInterface/Hydjet2Interface/interface/StrangeDensity.h"

NAStrangeDensity::NAStrangeDensity() {
  fTemperature = 0. * GeV;
  fBaryonPotential = 0. * GeV;
  fStrangePotential = 0. * GeV;
  fNMax = 5;
}
// compute hadron system strangeness density
double NAStrangeDensity::StrangenessDensity(DatabasePDG* database) {
  double meanStrangenessDensity = 0.;
  for (int particleIndex = 0; particleIndex < database->GetNParticles(); particleIndex++) {
    ParticlePDG* particle = database->GetPDGParticleByIndex(particleIndex);
    double particleDensity = ParticleNumberDensity(particle);
    meanStrangenessDensity += particleDensity * particle->GetStrangeness();
  }
  return meanStrangenessDensity;
}

// compute hadron number density
double NAStrangeDensity::ParticleNumberDensity(ParticlePDG* pDef) {
  double particleMass = pDef->GetMass();
  int particleStrangeness = int(pDef->GetStrangeness());
  double particleBaryon = pDef->GetBaryonNumber();
  //compute chemical potential
  double particleChemPotential = fBaryonPotential * particleBaryon + fStrangePotential * particleStrangeness;
  //compute degeneracy factor
  double particleDegFactor = 2 * pDef->GetSpin() + 1.;  // IA: In ParticlePDG() GetSpin() returns spin not 2*spin !!
  double d = 1.;                                        //for fermions
  if (int(2 * pDef->GetSpin()) % 2 == 0)  //it gives 0 for Spin = 0,2,4,.. and it gives 1 for Spin = 1,3,7,
    d = -1;                               //for bosons

  double prefactor;
  double postfactor;
  prefactor =
      (particleDegFactor * particleMass * particleMass * fTemperature / hbarc / hbarc / hbarc) / (2. * N_PI * N_PI);
  postfactor = 0.;

  for (int n = 1; n <= fNMax; n++) {
    postfactor += pow(-d, n + 1) / (n)*exp(n * particleChemPotential / fTemperature) *
                  HankelKn(2, n * particleMass / fTemperature);
  }
  return prefactor * postfactor;
}