#include <SiG4UniversalFluctuation.h>

Public Member Functions
double	SampleFluctuations (const double momentum, const double mass, double &tmax, const double length, const double meanLoss)

	SiG4UniversalFluctuation (CLHEP::HepRandomEngine &)

	~SiG4UniversalFluctuation ()

Private Attributes
double	alim

double	chargeSquare

double	e0

double	e1Fluct

double	e1LogFluct

double	e2Fluct

double	e2LogFluct

double	electronDensity

double	f1Fluct

double	f2Fluct

CLHEP::RandFlat *	flatDistribution

CLHEP::RandGaussQ *	gaussQDistribution

double	ipotFluct

double	ipotLogFluct

double	minLoss

double	minNumberInteractionsBohr

double	nmaxCont1

double	nmaxCont2

double	particleMass

CLHEP::RandPoisson *	poissonDistribution

double	problim

double	rateFluct

CLHEP::HepRandomEngine &	rndEngine

double	sumalim

double	theBohrBeta2

Detailed Description

Definition at line 67 of file SiG4UniversalFluctuation.h.

Constructor & Destructor Documentation

SiG4UniversalFluctuation::SiG4UniversalFluctuation ( CLHEP::HepRandomEngine & eng )

Definition at line 74 of file SiG4UniversalFluctuation.cc.

References chargeSquare, e0, e1Fluct, e1LogFluct, e2Fluct, e2LogFluct, electronDensity, f1Fluct, f2Fluct, flatDistribution, gaussQDistribution, ipotFluct, ipotLogFluct, create_public_lumi_plots::log, poissonDistribution, problim, rateFluct, rndEngine, and sumalim.

   :rndEngine(eng),
    gaussQDistribution(0),
    poissonDistribution(0),
    flatDistribution(0),
    minNumberInteractionsBohr(10.0),
    theBohrBeta2(50.0*keV/proton_mass_c2),
    minLoss(10.*eV),
    problim(5.e-3),  
    alim(10.),
    nmaxCont1(4.),
    nmaxCont2(16.)
 {
   sumalim = -log(problim);
   //lastMaterial = 0;
   
   // Add these definitions d.k.
   chargeSquare   = 1.;  //Assume all particles have charge 1
   // Taken from Geant4 printout, HARDWIRED for Silicon.
   ipotFluct = 0.0001736; //material->GetIonisation()->GetMeanExcitationEnergy();  
   electronDensity = 6.797E+20; // material->GetElectronDensity();
   f1Fluct      = 0.8571; // material->GetIonisation()->GetF1fluct();
   f2Fluct      = 0.1429; //material->GetIonisation()->GetF2fluct();
   e1Fluct      = 0.000116;// material->GetIonisation()->GetEnergy1fluct();
   e2Fluct      = 0.00196; //material->GetIonisation()->GetEnergy2fluct();
   e1LogFluct   = -9.063;  //material->GetIonisation()->GetLogEnergy1fluct();
   e2LogFluct   = -6.235;  //material->GetIonisation()->GetLogEnergy2fluct();
   rateFluct    = 0.4;     //material->GetIonisation()->GetRateionexcfluct();
   ipotLogFluct = -8.659;  //material->GetIonisation()->GetLogMeanExcEnergy();
   e0 = 1.E-5;             //material->GetIonisation()->GetEnergy0fluct();
   
   gaussQDistribution = new CLHEP::RandGaussQ(rndEngine);
   poissonDistribution = new CLHEP::RandPoisson(rndEngine);
   flatDistribution = new CLHEP::RandFlat(rndEngine);
 
   //cout << " init new fluct +++++++++++++++++++++++++++++++++++++++++"<<endl;
 }

SiG4UniversalFluctuation::~SiG4UniversalFluctuation ( )

Definition at line 117 of file SiG4UniversalFluctuation.cc.

References flatDistribution, gaussQDistribution, and poissonDistribution.

 {
   delete gaussQDistribution;
   delete poissonDistribution;
   delete flatDistribution;
 
 }

Member Function Documentation

double SiG4UniversalFluctuation::SampleFluctuations	(	const double	momentum,
		const double	mass,
		double &	tmax,
		const double	length,
		const double	meanLoss
	)

Definition at line 126 of file SiG4UniversalFluctuation.cc.

References alim, funct::C, chargeSquare, e0, e1Fluct, e1LogFluct, e2Fluct, e2LogFluct, electronDensity, f1Fluct, f2Fluct, flatDistribution, gam, gaussQDistribution, i, ipotFluct, ipotLogFluct, gen::k, create_public_lumi_plots::log, scaleCards::mass, max(), minLoss, minNumberInteractionsBohr, nmaxCont1, nmaxCont2, p1, p2, p3, particleMass, poissonDistribution, scaleCards::rate, rateFluct, mathSSE::sqrt(), sumalim, w(), w2, and vdt::x.

Referenced by SiLinearChargeDivider::fluctuateEloss(), and SiPixelDigitizerAlgorithm::fluctuateEloss().

 {
 // Calculate actual loss from the mean loss.
 // The model used to get the fluctuations is essentially the same
 // as in Glandz in Geant3 (Cern program library W5013, phys332).
 // L. Urban et al. NIM A362, p.416 (1995) and Geant4 Physics Reference Manual
 
   // shortcut for very very small loss (out of validity of the model)
   //
   if (meanLoss < minLoss) return meanLoss;
 
   //if(!particle) InitialiseMe(dp->GetDefinition());
   //G4double tau   = dp->GetKineticEnergy()/particleMass;
   //G4double gam   = tau + 1.0;
   //G4double gam2  = gam*gam;
   //G4double beta2 = tau*(tau + 2.0)/gam2;
 
   particleMass   = mass; // dp->GetMass();
   double gam2   = (momentum*momentum)/(particleMass*particleMass) + 1.0;
   double beta2 = 1.0 - 1.0/gam2;
   double gam = sqrt(gam2);
 
   double loss(0.), siga(0.);
   
   // Gaussian regime
   // for heavy particles only and conditions
   // for Gauusian fluct. has been changed 
   //
   if ((particleMass > electron_mass_c2) &&
       (meanLoss >= minNumberInteractionsBohr*tmax))
   {
     double massrate = electron_mass_c2/particleMass ;
     double tmaxkine = 2.*electron_mass_c2*beta2*gam2/
       (1.+massrate*(2.*gam+massrate)) ;
     if (tmaxkine <= 2.*tmax)   
     {
       //electronDensity = material->GetElectronDensity();
       siga  = (1.0/beta2 - 0.5) * twopi_mc2_rcl2 * tmax * length
                                 * electronDensity * chargeSquare;
       siga = sqrt(siga);
       double twomeanLoss = meanLoss + meanLoss;
       if (twomeanLoss < siga) {
         double x;
         do {
           loss = twomeanLoss*flatDistribution->fire();
           x = (loss - meanLoss)/siga;
         } while (1.0 - 0.5*x*x < flatDistribution->fire());
       } else {
         do {
           loss = gaussQDistribution->fire(meanLoss,siga);
         } while (loss < 0. || loss > twomeanLoss);
       }
       return loss;
     }
   }
 
   // Glandz regime : initialisation
   //
 //   if (material != lastMaterial) {
 //     f1Fluct      = material->GetIonisation()->GetF1fluct();
 //     f2Fluct      = material->GetIonisation()->GetF2fluct();
 //     e1Fluct      = material->GetIonisation()->GetEnergy1fluct();
 //     e2Fluct      = material->GetIonisation()->GetEnergy2fluct();
 //     e1LogFluct   = material->GetIonisation()->GetLogEnergy1fluct();
 //     e2LogFluct   = material->GetIonisation()->GetLogEnergy2fluct();
 //     rateFluct    = material->GetIonisation()->GetRateionexcfluct();
 //     ipotFluct    = material->GetIonisation()->GetMeanExcitationEnergy();
 //     ipotLogFluct = material->GetIonisation()->GetLogMeanExcEnergy();
 //     lastMaterial = material;
 //   }
 
   double a1 = 0. , a2 = 0., a3 = 0. ;
   double p1,p2,p3;
   double rate = rateFluct ;
 
   double w1 = tmax/ipotFluct;
   double w2 = log(2.*electron_mass_c2*beta2*gam2)-beta2;
 
   if(w2 > ipotLogFluct)
   {
     double C = meanLoss*(1.-rateFluct)/(w2-ipotLogFluct);
     a1 = C*f1Fluct*(w2-e1LogFluct)/e1Fluct;
     a2 = C*f2Fluct*(w2-e2LogFluct)/e2Fluct;
     if(a2 < 0.)
     {
       a1 = 0. ;
       a2 = 0. ;
       rate = 1. ;  
     }
   }
   else
   {
     rate = 1. ;
   }
 
   a3 = rate*meanLoss*(tmax-ipotFluct)/(ipotFluct*tmax*log(w1));
 
   double suma = a1+a2+a3;
   
   // Glandz regime
   //
   if (suma > sumalim)
   {
     p1 = 0., p2 = 0 ;
     if((a1+a2) > 0.)
     {
       // excitation type 1
       if (a1>alim) {
         siga=sqrt(a1) ;
         p1 = max(0.,gaussQDistribution->fire(a1,siga)+0.5);
       } else {
         p1 = double(poissonDistribution->fire(a1));
       }
     
       // excitation type 2
       if (a2>alim) {
         siga=sqrt(a2) ;
         p2 = max(0.,gaussQDistribution->fire(a2,siga)+0.5);
       } else {
         p2 = double(poissonDistribution->fire(a2));
       }
     
       loss = p1*e1Fluct+p2*e2Fluct;
  
       // smearing to avoid unphysical peaks
       if (p2 > 0.)
         loss += (1.-2.*flatDistribution->fire())*e2Fluct;
       else if (loss>0.)
         loss += (1.-2.*flatDistribution->fire())*e1Fluct;   
       if (loss < 0.) loss = 0.0;
     }
 
     // ionisation
     if (a3 > 0.) {
       if (a3>alim) {
         siga=sqrt(a3) ;
         p3 = max(0.,gaussQDistribution->fire(a3,siga)+0.5);
       } else {
         p3 = double(poissonDistribution->fire(a3));
       }
       double lossc = 0.;
       if (p3 > 0) {
         double na = 0.; 
         double alfa = 1.;
         if (p3 > nmaxCont2) {
           double rfac   = p3/(nmaxCont2+p3);
           double namean = p3*rfac;
           double sa     = nmaxCont1*rfac;
           na              = gaussQDistribution->fire(namean,sa);
           if (na > 0.) {
             alfa   = w1*(nmaxCont2+p3)/(w1*nmaxCont2+p3);
             double alfa1  = alfa*log(alfa)/(alfa-1.);
             double ea     = na*ipotFluct*alfa1;
             double sea    = ipotFluct*sqrt(na*(alfa-alfa1*alfa1));
             lossc += gaussQDistribution->fire(ea,sea);
           }
         }
 
         if (p3 > na) {
           w2 = alfa*ipotFluct;
           double w  = (tmax-w2)/tmax;
           int    nb = int(p3-na);
           for (int k=0; k<nb; k++) lossc += w2/(1.-w*flatDistribution->fire());
         }
       }        
       loss += lossc;  
     }
     return loss;
   }
   
   // suma < sumalim;  very small energy loss;  
   //
   //double e0 = material->GetIonisation()->GetEnergy0fluct();
 
   a3 = meanLoss*(tmax-e0)/(tmax*e0*log(tmax/e0));
   if (a3 > alim)
   {
     siga=sqrt(a3);
     p3 = max(0.,gaussQDistribution->fire(a3,siga)+0.5);
   } else {
     p3 = double(poissonDistribution->fire(a3));
   }
   if (p3 > 0.) {
     double w = (tmax-e0)/tmax;
     double corrfac = 1.;
     if (p3 > nmaxCont2) {
       corrfac = p3/nmaxCont2;
       p3 = nmaxCont2;
     } 
     int ip3 = (int)p3;
     for (int i=0; i<ip3; i++) loss += 1./(1.-w*flatDistribution->fire());
     loss *= e0*corrfac;
     // smearing for losses near to e0
     if(p3 <= 2.)
       loss += e0*(1.-2.*flatDistribution->fire()) ;
    }
     
    return loss;
 }