TG4SpecialUrbanMscModel.h

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#ifndef TG4SpecialUrbanMscModel_h
#define TG4SpecialUrbanMscModel_h 1
 
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// $Id:   $
// GEANT4 tag $Name:  $
//
// -------------------------------------------------------------------
//
//
// GEANT4 Class header file
//
//
// File name:     TG4SpecialUrbanMscModel
//
// Author:        Vladimir Ivanchenko adopt Laszlo Urban model for
//                ALICE requirements
//
// Creation date: 12.08.2015
//
 
// -------------------------------------------------------------------
//
 
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#include <CLHEP/Units/SystemOfUnits.h>
 
#include "G4Exp.hh"
#include "G4Log.hh"
#include "G4MscStepLimitType.hh"
#include "G4VMscModel.hh"
#include "G4Version.hh"
 
class G4ParticleChangeForMSC;
class G4SafetyHelper;
class G4LossTableManager;
 
namespace CLHEP
{
class HepRandomEngine;
}
 
static const G4double c_highland = 13.6 * CLHEP::MeV;
 
 
class TG4SpecialUrbanMscModel : public G4VMscModel
{
 
 public:
  TG4SpecialUrbanMscModel(const G4String& nam = "ALICEUrbanMsc");
 
  virtual ~TG4SpecialUrbanMscModel();
 
  void Initialise(const G4ParticleDefinition*, const G4DataVector&);
 
  void StartTracking(G4Track*);
 
  G4double ComputeCrossSectionPerAtom(const G4ParticleDefinition* particle,
    G4double KineticEnergy, G4double AtomicNumber, G4double AtomicWeight = 0.,
    G4double cut = 0., G4double emax = DBL_MAX);
 
  G4ThreeVector& SampleScattering(const G4ThreeVector&, G4double safety);
 
  G4double ComputeTruePathLengthLimit(
    const G4Track& track, G4double& currentMinimalStep);
 
  G4double ComputeGeomPathLength(G4double truePathLength);
 
  G4double ComputeTrueStepLength(G4double geomStepLength);
 
  inline G4double ComputeTheta0(
    G4double truePathLength, G4double KineticEnergy);
 
 private:
  G4double SampleCosineTheta(G4double trueStepLength, G4double KineticEnergy);
 
  inline void SetParticle(const G4ParticleDefinition*);
 
  inline void UpdateCache();
 
  inline G4double SimpleScattering(G4double xmeanth, G4double x2meanth);
 
  inline G4double LatCorrelation();
 
  //  hide assignment operator
  TG4SpecialUrbanMscModel& operator=(const TG4SpecialUrbanMscModel& right);
  TG4SpecialUrbanMscModel(const TG4SpecialUrbanMscModel&);
 
#if G4VERSION_NUMBER >= 1020
  CLHEP::HepRandomEngine* rndmEngineMod;
#endif
 
  const G4ParticleDefinition* particle;
  G4ParticleChangeForMSC* fParticleChange;
 
  const G4MaterialCutsCouple* couple;
  G4LossTableManager* theManager;
 
  G4double mass;
  G4double charge, ChargeSquare;
  G4double masslimite, lambdalimit, fr;
 
  G4double taubig;
  G4double tausmall;
  G4double taulim;
  G4double currentTau;
  G4double tlimit;
  G4double tlimitmin;
  G4double tlimitminfix, tlimitminfix2;
  G4double tgeom;
 
  G4double geombig;
  G4double geommin;
  G4double geomlimit;
  G4double skindepth;
  G4double smallstep;
 
  G4double presafety;
 
  G4double lambda0;
  G4double lambdaeff;
  G4double tPathLength;
  G4double zPathLength;
  G4double par1, par2, par3;
 
  G4double stepmin;
 
  G4double currentKinEnergy;
  G4double currentRange;
  G4double rangeinit;
  G4double currentRadLength;
 
  G4double theta0max, rellossmax;
  G4double third;
 
  G4int currentMaterialIndex;
 
  G4double y;
  G4double Zold;
  G4double Zeff, Z2, Z23, lnZ;
  G4double coeffth1, coeffth2;
  G4double coeffc1, coeffc2, coeffc3, coeffc4;
 
  G4bool firstStep;
  G4bool inside;
  G4bool insideskin;
 
  G4bool latDisplasmentbackup;
 
  G4double rangecut;
  G4double drr, finalr;
};
 
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inline void TG4SpecialUrbanMscModel::SetParticle(const G4ParticleDefinition* p)
{
  if (p != particle) {
    particle = p;
    mass = p->GetPDGMass();
    charge = p->GetPDGCharge() / CLHEP::eplus;
    ChargeSquare = charge * charge;
  }
}
 
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inline void TG4SpecialUrbanMscModel::UpdateCache()
{
  lnZ = G4Log(Zeff);
  // correction in theta0 formula
  G4double w = G4Exp(lnZ / 6.);
  G4double facz = 0.990395 + w * (-0.168386 + w * 0.093286);
  coeffth1 = facz * (1. - 8.7780e-2 / Zeff);
  coeffth2 = facz * (4.0780e-2 + 1.7315e-4 * Zeff);
 
  // tail parameters
  G4double Z13 = w * w;
  coeffc1 = 2.3785 - Z13 * (4.1981e-1 - Z13 * 6.3100e-2);
  coeffc2 = 4.7526e-1 + Z13 * (1.7694 - Z13 * 3.3885e-1);
  coeffc3 = 2.3683e-1 - Z13 * (1.8111 - Z13 * 3.2774e-1);
  coeffc4 = 1.7888e-2 + Z13 * (1.9659e-2 - Z13 * 2.6664e-3);
 
  Z2 = Zeff * Zeff;
  Z23 = Z13 * Z13;
 
  Zold = Zeff;
}
 
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inline G4double TG4SpecialUrbanMscModel::ComputeTheta0(
  G4double trueStepLength, G4double KineticEnergy)
{
  // for all particles take the width of the central part
  //  from a  parametrization similar to the Highland formula
  // ( Highland formula: Particle Physics Booklet, July 2002, eq. 26.10)
  G4double invbetacp =
    std::sqrt((currentKinEnergy + mass) * (KineticEnergy + mass) /
              (currentKinEnergy * (currentKinEnergy + 2. * mass) *
                KineticEnergy * (KineticEnergy + 2. * mass)));
  y = trueStepLength / currentRadLength;
  G4double theta0 = c_highland * std::abs(charge) * std::sqrt(y) * invbetacp;
  y = G4Log(y);
  // correction factor from e- scattering data
  theta0 *= (coeffth1 + coeffth2 * y);
  return theta0;
}
 
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inline G4double TG4SpecialUrbanMscModel::SimpleScattering(
  G4double xmeanth, G4double x2meanth)
{
  // 'large angle scattering'
  // 2 model functions with correct xmean and x2mean
  G4double a =
    (2. * xmeanth + 9. * x2meanth - 3.) / (2. * xmeanth - 3. * x2meanth + 1.);
  G4double prob = (a + 2.) * xmeanth / a;
 
  // sampling
  G4double cth = 1.;
  if (rndmEngineMod->flat() < prob) {
    cth = -1. + 2. * G4Exp(G4Log(rndmEngineMod->flat()) / (a + 1.));
  }
  else {
    cth = -1. + 2. * rndmEngineMod->flat();
  }
  return cth;
}
 
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inline G4double TG4SpecialUrbanMscModel::LatCorrelation()
{
  static const G4double kappa = 2.5;
  static const G4double kappami1 = 1.5;
 
  G4double latcorr = 0.;
  if ((currentTau >= tausmall) && !insideskin) {
    if (currentTau < taulim)
      latcorr = lambdaeff * kappa * currentTau * currentTau *
                (1. - (kappa + 1.) * currentTau * third) * third;
    else {
      G4double etau = 0.;
      if (currentTau < taubig) {
        etau = G4Exp(-currentTau);
      }
      latcorr = -kappa * currentTau;
      latcorr = G4Exp(latcorr) / kappami1;
      latcorr += 1. - kappa * etau / kappami1;
      latcorr *= 2. * lambdaeff * third;
    }
  }
  return latcorr;
}
 
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#endif