RkFitMaterial.cxx

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//-----------------------------------------------------------------------
// File from KalFit module
//
// Filename : RkFitMaterial.cc
//------------------------------------------------------------------------
// Description :
// Material is a class which describes the properties of a given material,
// for instance atomic number, atomic weight and so on.
//------------------------------------------------------------------------
// Modif :
//------------------------------------------------------------------------
#include "TrkReco/RkFitMaterial.h"
#include <iostream>
#include <math.h>
 
using namespace std;
 
RkFitMaterial::RkFitMaterial( double z, double a, double i, double rho, double x0 )
    : x0_( x0 )
    , z_( z ) // rho is the density, z is the atomic number, a is the weight
              // i is mean excitation potention, x0 is the radiation length
{
  rza_ = rho * z / a;
  isq_ = i * i * 1e-18;
}
 
RkFitMaterial::RkFitMaterial( const RkFitMaterial& mat )
    : rza_( mat.rza_ ), isq_( mat.isq_ ), x0_( mat.x0_ ), z_( mat.z_ ) {}
 
// calculate dE
double RkFitMaterial::dE( double mass, double path, double p ) const {
  if ( !( p > 0 ) ) return 0;
 
  // cout<<"this material:x0 "<< x0_ << " Z  " << z_ << endl
  //     <<"  rho*Z/A  "<< rza_ << " I^2 "<< isq_ << endl;
 
  const double Me  = 0.000510999;
  double       psq = p * p;
  double       bsq = psq / ( psq + mass * mass );
  double       esq = psq / ( mass * mass );
 
  double s = Me / mass;
  double w = ( 4 * Me * esq / ( 1 + 2 * s * sqrt( 1 + esq ) + s * s ) );
  // Density correction :
  double cc, x0;
  cc = 1 + 2 * log( sqrt( isq_ ) / ( 28.8E-09 * sqrt( rza_ ) ) );
  if ( cc < 5.215 ) x0 = 0.2;
  else x0 = 0.326 * cc - 1.5;
  double x1( 3 ), xa( cc / 4.606 ), aa;
  aa = 4.606 * ( xa - x0 ) / ( ( x1 - x0 ) * ( x1 - x0 ) * ( x1 - x0 ) );
  double delta( 0 );
  double x( log10( sqrt( esq ) ) );
  if ( x > x0 )
  {
    delta = 4.606 * x - cc;
    if ( x < x1 ) delta = delta + aa * ( x1 - x ) * ( x1 - x ) * ( x1 - x );
  }
  // Shell correction :
  float f1, f2, f3, f4, f5, ce;
  f1 = 1 / esq;
  f2 = f1 * f1;
  f3 = f1 * f2;
  f4 = ( f1 * 0.42237 + f2 * 0.0304 - f3 * 0.00038 ) * 1E12;
  f5 = ( f1 * 3.858 - f2 * 0.1668 + f3 * 0.00158 ) * 1E18;
  ce = f4 * isq_ + f5 * isq_ * sqrt( isq_ );
  return ( 0.0001535 * rza_ / bsq *
           ( log( Me * esq * w / isq_ ) - 2 * bsq - delta - 2.0 * ce / z_ ) ) *
         path;
}
 
// calculate Multiple Scattering angle
double RkFitMaterial::mcs_angle( double mass, double path, double p ) const {
  // cout<<"this material:x0 "<< x0_ << " Z  " << z_ << endl
  //     <<"  rho*Z/A  "<< rza_ << " I^2 "<< isq_ << endl;
  double t   = path / x0_;
  double psq = p * p;
  return 0.0136 * sqrt( t * ( mass * mass + psq ) ) / psq * ( 1 + 0.038 * log( t ) );
}
 
// calculate the RMS of straggling for the energy loss (del_E) :
double RkFitMaterial::del_E( double mass, double path, double p ) const {
  double sigma0_2 = 0.1569 * rza_ * path;
 
  if ( sigma0_2 < 0 ) return 0;
 
  double psq = p * p;
  double bsq = psq / ( psq + mass * mass );
 
  // Correction for relativistic particles :
  double sigma_2 = sigma0_2 * ( 1 - 0.5 * bsq ) / ( 1 - bsq );
 
  if ( sigma_2 < 0 ) return 0;
 
  // Return sigma in GeV !!
  return sqrt( sigma_2 ) * 0.001;
}