//
// ********************************************************************
// * License and Disclaimer                                           *
// *                                                                  *
// * The  Geant4 software  is  copyright of the Copyright Holders  of *
// * the Geant4 Collaboration.  It is provided  under  the terms  and *
// * conditions of the Geant4 Software License,  included in the file *
// * LICENSE and available at  http://cern.ch/geant4/license .  These *
// * include a list of copyright holders.                             *
// *                                                                  *
// * Neither the authors of this software system, nor their employing *
// * institutes,nor the agencies providing financial support for this *
// * work  make  any representation or  warranty, express or implied, *
// * regarding  this  software system or assume any liability for its *
// * use.  Please see the license in the file  LICENSE  and URL above *
// * for the full disclaimer and the limitation of liability.         *
// *                                                                  *
// * This  code  implementation is the result of  the  scientific and *
// * technical work of the GEANT4 collaboration.                      *
// * By using,  copying,  modifying or  distributing the software (or *
// * any work based  on the software)  you  agree  to acknowledge its *
// * use  in  resulting  scientific  publications,  and indicate your *
// * acceptance of all terms of the Geant4 Software license.          *
// ********************************************************************
//
//
// Geant4 Header : G4AntiNuclElastic
//
// 

#include "G4AntiNuclElastic.hh"

#include "G4PhysicalConstants.hh"
#include "G4SystemOfUnits.hh"
#include "G4ParticleTable.hh"
#include "G4ParticleDefinition.hh"
#include "G4IonTable.hh"
#include "Randomize.hh"
#include "G4AntiProton.hh"
#include "G4AntiNeutron.hh"
#include "G4AntiDeuteron.hh"
#include "G4AntiAlpha.hh"
#include "G4AntiTriton.hh"
#include "G4AntiHe3.hh"
#include "G4Proton.hh"
#include "G4Neutron.hh"
#include "G4Deuteron.hh"
#include "G4Alpha.hh"
#include "G4Pow.hh"
#include "G4Exp.hh"
#include "G4Log.hh"

#include "G4NucleiProperties.hh"
#include "G4CrossSectionDataSetRegistry.hh"

G4AntiNuclElastic::G4AntiNuclElastic() 
  : G4HadronElastic("AntiAElastic")
{
  //V.Ivanchenko commented out 
  //SetMinEnergy( 0.1*GeV );
  //SetMaxEnergy( 10.*TeV );

  theAProton       = G4AntiProton::AntiProton();
  theANeutron      = G4AntiNeutron::AntiNeutron();
  theADeuteron     = G4AntiDeuteron::AntiDeuteron();
  theATriton       = G4AntiTriton::AntiTriton();
  theAAlpha        = G4AntiAlpha::AntiAlpha();
  theAHe3          = G4AntiHe3::AntiHe3();

  theProton   = G4Proton::Proton();
  theNeutron  = G4Neutron::Neutron();
  theDeuteron = G4Deuteron::Deuteron();
  theAlpha    = G4Alpha::Alpha();

  G4CrossSectionDataSetRegistry* reg = G4CrossSectionDataSetRegistry::Instance();
  cs = static_cast<G4ComponentAntiNuclNuclearXS*>(reg->GetComponentCrossSection("AntiAGlauber"));
  if(!cs) { cs = new G4ComponentAntiNuclNuclearXS(); }

  fParticle = 0;
  fWaveVector = 0.;
  fBeta = 0.;
  fZommerfeld = 0.;
  fAm = 0.;
  fTetaCMS = 0.;    
  fRa = 0.;
  fRef = 0.;
  fceff = 0.;
  fptot = 0.;
  fTmax = 0.;
  fThetaLab = 0.;
}

/////////////////////////////////////////////////////////////////////////
G4AntiNuclElastic::~G4AntiNuclElastic()
{}

////////////////////////////////////////////////////////////////////////
// sample momentum transfer in the CMS system 
G4double G4AntiNuclElastic::SampleInvariantT(const G4ParticleDefinition* particle, 
					     G4double Plab,  G4int Z, G4int A)
{
  G4double T;
  G4double Mproj = particle->GetPDGMass();
  G4LorentzVector Pproj(0.,0.,Plab,std::sqrt(Plab*Plab+Mproj*Mproj));
  G4double ctet1 = GetcosTeta1(Plab, A); 

  G4double energy=Pproj.e()-Mproj;   
  
  const G4ParticleDefinition* theParticle = particle;

  G4ParticleDefinition * theTargetDef = 0;

  if      (Z == 1 && A == 1) theTargetDef = theProton;
  else if (Z == 1 && A == 2) theTargetDef = theDeuteron;
  else if (Z == 1 && A == 3) theTargetDef = G4Triton::Triton();
  else if (Z == 2 && A == 3) theTargetDef = G4He3::He3();
  else if (Z == 2 && A == 4) theTargetDef = theAlpha;


  G4double TargMass =G4NucleiProperties::GetNuclearMass(A,Z); 

  //transform to CMS

  G4LorentzVector lv(0.0,0.0,0.0,TargMass);   
  lv += Pproj;
  G4double S = lv.mag2()/(GeV*GeV);

  G4ThreeVector bst = lv.boostVector();
  Pproj.boost(-bst);

  G4ThreeVector p1 = Pproj.vect();
  G4double ptot    = p1.mag();

  fbst = bst;
  fptot= ptot;
  fTmax = 4.0*ptot*ptot;  // In (MeV/c)^2

  if(Plab < (std::abs(particle->GetBaryonNumber())*100)*MeV)
  {return fTmax*G4UniformRand();}
  
  // Calculation of NN collision properties
  G4double PlabPerN = Plab/std::abs(theParticle->GetBaryonNumber());
  G4double NucleonMass = 0.5*( theProton->GetPDGMass() + theNeutron->GetPDGMass() );
  G4double PrNucleonMass(0.);  // Projectile average nucleon mass
  if( std::abs(theParticle->GetBaryonNumber()) == 1 ) { PrNucleonMass = theParticle->GetPDGMass(); }
  else                                                { PrNucleonMass = NucleonMass;               }
  G4double energyPerN = std::sqrt( sqr(PlabPerN) + sqr(PrNucleonMass));
  energyPerN -= PrNucleonMass;
  //---

  G4double  Z1 = particle->GetPDGCharge();
  G4double  Z2 = Z;  
  
  G4double beta = CalculateParticleBeta(particle, ptot); 
  G4double n  = CalculateZommerfeld( beta,  Z1,  Z2 );
  G4double Am = CalculateAm( ptot,  n,  Z2 );
  fWaveVector = ptot;     //   /hbarc; 
	    
  G4LorentzVector Fproj(0.,0.,0.,0.);  
  const G4double mevToBarn = 0.38938e+6;
  G4double XsCoulomb = mevToBarn*sqr(n/fWaveVector)*pi*(1+ctet1)/(1.+Am)/(1.+2.*Am-ctet1);

  G4double XsElastHadronic =cs->GetElasticElementCrossSection(particle, energy, Z, (G4double)A);
  G4double XsTotalHadronic =cs->GetTotalElementCrossSection(particle, energy, Z, (G4double)A);

  XsElastHadronic/=millibarn; XsTotalHadronic/=millibarn;

  G4double CoulombProb =  XsCoulomb/(XsCoulomb+XsElastHadronic);

  if(G4UniformRand() < CoulombProb)
  {  // Simulation of Coulomb scattering

    G4double phi = twopi * G4UniformRand();
    G4double Ksi =  G4UniformRand();

    G4double par1 = 2.*(1.+Am)/(1.+ctet1);

    // ////sample ThetaCMS in Coulomb part

    G4double cosThetaCMS = (par1*ctet1- Ksi*(1.+2.*Am))/(par1-Ksi);

    G4double PtZ=ptot*cosThetaCMS;
    Fproj.setPz(PtZ);
    G4double PtProjCMS = ptot*std::sqrt(1.0 - cosThetaCMS*cosThetaCMS);
    G4double PtX= PtProjCMS * std::cos(phi);
    G4double PtY= PtProjCMS * std::sin(phi);
    Fproj.setPx(PtX);     
    Fproj.setPy(PtY);
    Fproj.setE(std::sqrt(PtX*PtX+PtY*PtY+PtZ*PtZ+Mproj*Mproj));    
    T =  -(Pproj-Fproj).mag2();      
  } 
  else 
  {  
    // Simulation of strong interaction scattering

    G4double Qmax = 2.*ptot/197.33;   // in fm^-1

    G4double Amag      = 1.0;  // A1 in Majorant funct:A1*exp(-q*A2)
    G4double SlopeMag  = 0.5;  // A2 in Majorant funct:A1*exp(-q*A2)
    
    G4double sig_pbarp = cs->GetAntiHadronNucleonTotCrSc(theAProton,energyPerN);  //mb

    fRa = 1.113*G4Pow::GetInstance()->Z13(A) -                     
          0.227/G4Pow::GetInstance()->Z13(A);                      
    if(A == 3) fRa=1.81;
    if(A == 4) fRa=1.37;
 
    if((A>=12.) && (A<27) ) fRa=fRa*0.85;
    if((A>=27.) && (A<48) ) fRa=fRa*0.90;
    if((A>=48.) && (A<65) ) fRa=fRa*0.95;

    G4double Ref2 = XsTotalHadronic/10./2./pi;  // in fm^2
    G4double ceff2 =0;
    G4double rho = 0;

    if  ((theParticle == theAProton) || (theParticle == theANeutron))  
    {
      if(theTargetDef == theProton)
      { 
        // Determination of the real part of Pbar+N amplitude
        if(Plab < 610.) 
        { rho = 1.3347-10.342*Plab/1000.+22.277*Plab/1000.*Plab/1000.-
                13.634*Plab/1000.*Plab/1000.*Plab/1000. ;}
        if((Plab < 5500.)&&(Plab >= 610.) )
        { rho = 0.22; }
        if((Plab >= 5500.)&&(Plab < 12300.) )
        { rho = -0.32; }
        if( Plab >= 12300.)
        { rho = 0.135-2.26/(std::sqrt(S)) ;}
        Ref2  = 0.35 + 0.9/std::sqrt(std::sqrt(S-4.*0.88))+0.04*G4Log(S) ;
        ceff2 = 0.375 - 2./S + 0.44/(sqr(S-4.)+1.5) ;
        Ref2  =Ref2*Ref2;
        ceff2 = ceff2*ceff2;
      }

      if( (Z==1)&&(A==2) )
      {
        Ref2 = fRa*fRa - 0.28 + 0.019 * sig_pbarp + 2.06e-6 * sig_pbarp*sig_pbarp;  
        ceff2 = 0.297 + 7.853e-04*sig_pbarp + 0.2899*G4Exp(-0.03*sig_pbarp);
      }
      if( (Z==1)&&(A==3) )
      { 
        Ref2 = fRa*fRa - 1.36 + 0.025 * sig_pbarp - 3.69e-7 * sig_pbarp*sig_pbarp;
        ceff2 = 0.149 + 7.091e-04*sig_pbarp + 0.3743*G4Exp(-0.03*sig_pbarp);
      }
      if( (Z==2)&&(A==3) )
      { 
        Ref2 = fRa*fRa - 1.36 + 0.025 * sig_pbarp - 3.69e-7 * sig_pbarp*sig_pbarp;
        ceff2 = 0.149 + 7.091e-04*sig_pbarp + 0.3743*G4Exp(-0.03*sig_pbarp);
      }  
      if( (Z==2)&&(A==4) )
      { 
        Ref2 = fRa*fRa -0.46 +0.03*sig_pbarp - 2.98e-6*sig_pbarp*sig_pbarp;
        ceff2= 0.078 + 6.657e-4*sig_pbarp + 0.3359*G4Exp(-0.03*sig_pbarp);
      }
      if(Z>2) 
      { 
        Ref2 = fRa*fRa +2.48*0.01*sig_pbarp*fRa - 2.23e-6*sig_pbarp*sig_pbarp*fRa*fRa; 
        ceff2 = 0.16+3.3e-4*sig_pbarp+0.35*G4Exp(-0.03*sig_pbarp);
      }
    }  // End of if ((theParticle == theAProton) || (theParticle == theANeutron))

    if (theParticle == theADeuteron)
    {
      if(theTargetDef == theProton)
      { 
        ceff2 = 0.297 + 7.853e-04*sig_pbarp + 0.2899*G4Exp(-0.03*sig_pbarp);
      }
      if(theTargetDef == theDeuteron)
      { 
        ceff2 = 0.65 + 3.0e-4*sig_pbarp + 0.55 * G4Exp(-0.03*sig_pbarp);
      }
      if( (theTargetDef == G4Triton::Triton()) || (theTargetDef == G4He3::He3() ) )
      {
        ceff2 = 0.57 + 2.5e-4*sig_pbarp + 0.65 * G4Exp(-0.02*sig_pbarp);
      }
      if(theTargetDef == theAlpha)
      {
        ceff2 = 0.40 + 3.5e-4 *sig_pbarp + 0.45 * G4Exp(-0.02*sig_pbarp);
      }
      if(Z>2)
      {
        ceff2 = 0.38 + 2.0e-4 *sig_pbarp + 0.5 * G4Exp(-0.03*sig_pbarp);
      }
    }

    if( (theParticle ==theAHe3) || (theParticle ==theATriton) )
    {
      if(theTargetDef == theProton)
      {
        ceff2 = 0.149 + 7.091e-04*sig_pbarp + 0.3743*G4Exp(-0.03*sig_pbarp);         
      }
      if(theTargetDef == theDeuteron)
      {
        ceff2 = 0.57 + 2.5e-4*sig_pbarp + 0.65 * G4Exp(-0.02*sig_pbarp);
      }
      if( (theTargetDef == G4Triton::Triton()) || (theTargetDef == G4He3::He3() ) )
      {
        ceff2 = 0.39 + 2.7e-4*sig_pbarp + 0.7 * G4Exp(-0.02*sig_pbarp);
      }
      if(theTargetDef == theAlpha)
      {
        ceff2 = 0.24 + 3.5e-4*sig_pbarp + 0.75 * G4Exp(-0.03*sig_pbarp);
      }
      if(Z>2)
      {
        ceff2 = 0.26 + 2.2e-4*sig_pbarp + 0.33*G4Exp(-0.03*sig_pbarp);
      }  
    }

    if (theParticle == theAAlpha)
    {
      if(theTargetDef == theProton)
      {
        ceff2= 0.078 + 6.657e-4*sig_pbarp + 0.3359*G4Exp(-0.03*sig_pbarp);   
      }
      if(theTargetDef == theDeuteron)  
      {
        ceff2 = 0.40 + 3.5e-4 *sig_pbarp + 0.45 * G4Exp(-0.02*sig_pbarp);
      }   
      if( (theTargetDef == G4Triton::Triton()) || (theTargetDef == G4He3::He3() ) )
      {
        ceff2 = 0.24 + 3.5e-4*sig_pbarp + 0.75 * G4Exp(-0.03*sig_pbarp);   
      }
      if(theTargetDef == theAlpha)   
      {
        ceff2 = 0.17 + 3.5e-4*sig_pbarp + 0.45 * G4Exp(-0.03*sig_pbarp);
      }
      if(Z>2)
      {
        ceff2 = 0.22 + 2.0e-4*sig_pbarp + 0.2 * G4Exp(-0.03*sig_pbarp);
      }
    }

    fRef=std::sqrt(Ref2);
    fceff = std::sqrt(ceff2);     

    G4double Q = 0.0 ;
    G4double BracFunct;

    const G4int maxNumberOfLoops = 10000;
    G4int loopCounter = 0;
    do 
    {
      Q = -G4Log(1.-(1.- G4Exp(-SlopeMag * Qmax))* G4UniformRand() )/SlopeMag;
      G4double x = fRef * Q;
      BracFunct = ( ( sqr(BesselOneByArg(x))+sqr(rho/2. * BesselJzero(x)) )
		    *   sqr(DampFactor(pi*fceff*Q))) /(Amag*G4Exp(-SlopeMag*Q));
      BracFunct = BracFunct * Q;
    } 
    while ( (G4UniformRand()>BracFunct) && 
            ++loopCounter < maxNumberOfLoops );  /* Loop checking, 10.08.2015, A.Ribon */
    if ( loopCounter >= maxNumberOfLoops ) {
      fTetaCMS = 0.0;
      return 0.0;
    }

    T= sqr(Q); 
    T*=3.893913e+4;  // fm^(-2) -> MeV^2

  }  // End of simulation of strong interaction scattering

  return T;
}

/////////////////////////////////////////////////////////////////////
//  Sample of Theta in CMS
 G4double G4AntiNuclElastic::SampleThetaCMS(const G4ParticleDefinition* p, G4double plab,
                                                                         G4int Z, G4int A)
{ 
  G4double T;
  T =  SampleInvariantT( p, plab,  Z,  A);

   // NaN finder
  if(!(T < 0.0 || T >= 0.0))
  {
    if (verboseLevel > 0)
    {
      G4cout << "G4DiffuseElastic:WARNING: A = " << A
             << " mom(GeV)= " << plab/GeV
             << " S-wave will be sampled"
             << G4endl;
    }
    T = G4UniformRand()*fTmax;
 
  }

  if(fptot > 0.)
  {
   G4double cosTet=1.0-T/(2.*fptot*fptot);
   if(cosTet >  1.0 ) cosTet= 1.;
   if(cosTet < -1.0 ) cosTet=-1.;
   fTetaCMS=std::acos(cosTet); 
   return fTetaCMS;
  } else
  {
   return 2.*G4UniformRand()-1.;
  }
}  


/////////////////////////////////////////////////////////////////////
//  Sample of Theta in Lab System
 G4double G4AntiNuclElastic::SampleThetaLab(const G4ParticleDefinition* p, G4double plab,
                                                                         G4int Z, G4int A)
{ 
  G4double T; 
  T = SampleInvariantT( p, plab,  Z,  A);

 // NaN finder
  if(!(T < 0.0 || T >= 0.0))
  {
    if (verboseLevel > 0)               
    {
      G4cout << "G4DiffuseElastic:WARNING: A = " << A
             << " mom(GeV)= " << plab/GeV
             << " S-wave will be sampled"
             << G4endl;
    }
    T = G4UniformRand()*fTmax;
  }

  G4double phi  = G4UniformRand()*twopi;

  G4double cost(1.);
  if(fTmax > 0.) {cost = 1. - 2.0*T/fTmax;}

  G4double sint;
  if( cost >= 1.0 )
  {
    cost = 1.0;
    sint = 0.0;
  }
  else if( cost <= -1.0)
  {
    cost = -1.0;
    sint =  0.0;
  }
  else
  {
    sint = std::sqrt((1.0-cost)*(1.0+cost));
  }

  G4double m1 = p->GetPDGMass();
  G4ThreeVector v(sint*std::cos(phi),sint*std::sin(phi),cost);
  v *= fptot;
  G4LorentzVector nlv(v.x(),v.y(),v.z(),std::sqrt(fptot*fptot + m1*m1));
   
  nlv.boost(fbst);
   
  G4ThreeVector np = nlv.vect();
  G4double theta = np.theta();
  fThetaLab = theta; 

  return theta;
}

////////////////////////////////////////////////////////////////////
//   Calculation of Damp factor
 G4double G4AntiNuclElastic::DampFactor(G4double x)
{
   G4double df;
   G4double  f3 = 6.; // first factorials

 if( std::fabs(x) < 0.01 )
  { 
      df=1./(1.+x*x/f3); 
 }
  else
  {
    df = x/std::sinh(x); 
  }
  return df;
}


/////////////////////////////////////////////////////////////////////////////////
//  Calculation of particle velocity Beta

 G4double G4AntiNuclElastic::CalculateParticleBeta( const G4ParticleDefinition* particle, 
                                 	G4double momentum    )
{
  G4double mass = particle->GetPDGMass();
  G4double a    = momentum/mass;
  fBeta         = a/std::sqrt(1+a*a);

  return fBeta; 
}


///////////////////////////////////////////////////////////////////////////////////
//   Calculation of parameter Zommerfeld

 G4double G4AntiNuclElastic::CalculateZommerfeld( G4double beta, G4double Z1, G4double Z2 )
{
  fZommerfeld = fine_structure_const*Z1*Z2/beta;

  return fZommerfeld; 
}

////////////////////////////////////////////////////////////////////////////////////
//  
G4double G4AntiNuclElastic::CalculateAm( G4double momentum, G4double n, G4double Z)
{
  G4double k   = momentum/hbarc;
  G4double ch  = 1.13 + 3.76*n*n;
  G4double zn  = 1.77*k/G4Pow::GetInstance()->A13(Z)*Bohr_radius; 
  G4double zn2 = zn*zn;
  fAm          = ch/zn2;

  return fAm;
}

/////////////////////////////////////////////////////////////
//
// Bessel J0 function based on rational approximation from
// J.F. Hart, Computer Approximations, New York, Willey 1968, p. 141
   
G4double G4AntiNuclElastic::BesselJzero(G4double value)
{  
  G4double modvalue, value2, fact1, fact2, arg, shift, bessel;

  modvalue = std::fabs(value);

  if ( value < 8.0 && value > -8.0 )
  {
    value2 = value*value;
                 
    fact1  = 57568490574.0 + value2*(-13362590354.0
                           + value2*( 651619640.7  
                           + value2*(-11214424.18
                           + value2*( 77392.33017
                           + value2*(-184.9052456   ) ) ) ) );
                              
    fact2  = 57568490411.0 + value2*( 1029532985.0
                           + value2*( 9494680.718
                           + value2*(59272.64853
                           + value2*(267.8532712
                           + value2*1.0               ) ) ) );
 
    bessel = fact1/fact2;
  }
  else
  {
    arg    = 8.0/modvalue;

    value2 = arg*arg;
 
    shift  = modvalue-0.785398164;

    fact1  = 1.0 + value2*(-0.1098628627e-2
                 + value2*(0.2734510407e-4
                 + value2*(-0.2073370639e-5
                 + value2*0.2093887211e-6    ) ) );
  fact2  = -0.1562499995e-1 + value2*(0.1430488765e-3
                              + value2*(-0.6911147651e-5
                              + value2*(0.7621095161e-6
                              - value2*0.934945152e-7    ) ) );

    bessel = std::sqrt(0.636619772/modvalue)*(std::cos(shift)*fact1 - arg*std::sin(shift)*fact2);
  }
  return bessel;
}


//////////////////////////////////////////////////////////////////////////////
// Bessel J1 function based on rational approximation from
// J.F. Hart, Computer Approximations, New York, Willey 1968, p. 141
    
 G4double G4AntiNuclElastic::BesselJone(G4double value)
{
  G4double modvalue, value2, fact1, fact2, arg, shift, bessel;
                          
  modvalue = std::fabs(value);
                 
  if ( modvalue < 8.0 )
  {
    value2 = value*value;
    fact1  = value*(72362614232.0 + value2*(-7895059235.0
                                  + value2*( 242396853.1
                                  + value2*(-2972611.439
                                  + value2*( 15704.48260
                                  + value2*(-30.16036606  ) ) ) ) ) );
    
    fact2  = 144725228442.0 + value2*(2300535178.0
                            + value2*(18583304.74
                            + value2*(99447.43394
                            + value2*(376.9991397
                            + value2*1.0             ) ) ) );
    bessel = fact1/fact2;
  }
  else
  {
    arg    = 8.0/modvalue;  
  value2 = arg*arg;

    shift  = modvalue - 2.356194491;

    fact1  = 1.0 + value2*( 0.183105e-2
                 + value2*(-0.3516396496e-4
                 + value2*(0.2457520174e-5
                 + value2*(-0.240337019e-6          ) ) ) );

    fact2 = 0.04687499995 + value2*(-0.2002690873e-3
                          + value2*( 0.8449199096e-5
                          + value2*(-0.88228987e-6
                          + value2*0.105787412e-6       ) ) );

    bessel = std::sqrt( 0.636619772/modvalue)*(std::cos(shift)*fact1 - arg*std::sin(shift)*fact2);
    if (value < 0.0) bessel = -bessel;
  }
  return bessel;
}

////////////////////////////////////////////////////////////////////////////////
// return J1(x)/x with special case for small x 
G4double G4AntiNuclElastic::BesselOneByArg(G4double x)
{
  G4double x2, result;
 
  if( std::fabs(x) < 0.01 )
  {
   x  *= 0.5;
   x2 = x*x;
   result = (2.- x2 + x2*x2/6.)/4.;
  }
  else
  {
    result = BesselJone(x)/x;
  }
  return result;
} 

/////////////////////////////////////////////////////////////////////////////////
// return  angle from which Coulomb scattering is calculated 
G4double G4AntiNuclElastic::GetcosTeta1(G4double plab, G4int A)
{

// G4double p0 =G4LossTableManager::Instance()->FactorForAngleLimit()*CLHEP::hbarc/CLHEP::fermi;
  G4double p0 = 1.*hbarc/fermi;
//G4double cteta1 = 1.0 - p0*p0/2.0 * pow(A,2./3.)/(plab*plab);
  G4double cteta1 = 1.0 - p0*p0/2.0 * G4Pow::GetInstance()->Z23(A)/(plab*plab);
//////////////////
  if(cteta1 < -1.) cteta1 = -1.0;
  return cteta1;
}