narrowResonanceCrossSection.cpp

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//
//    Copyright 2010
//
//    This file is part of starlight.
//
//    starlight is free software: you can redistribute it and/or modify
//    it under the terms of the GNU General Public License as published by
//    the Free Software Foundation, either version 3 of the License, or
//    (at your option) any later version.
//
//    starlight is distributed in the hope that it will be useful,
//    but WITHOUT ANY WARRANTY; without even the implied warranty of
//    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
//    GNU General Public License for more details.
//
//    You should have received a copy of the GNU General Public License
//    along with starlight. If not, see <http://www.gnu.org/licenses/>.
//
//
// File and Version Information:
// $Rev:: 264                         $: revision of last commit
// $Author:: jseger                   $: author of last commit
// $Date:: 2016-06-06 21:05:12 +0100 #$: date of last commit
//
// Description:
//
//
//


#include <iostream>
#include <iomanip>
#include <fstream>
#include <cmath>

#include "starlightconstants.h"
#include "narrowResonanceCrossSection.h"


using namespace std;
using namespace starlightConstants;


//______________________________________________________________________________
narrowResonanceCrossSection::narrowResonanceCrossSection(const inputParameters& inputParametersInstance, const beamBeamSystem&  bbsystem)
  :photonNucleusCrossSection(inputParametersInstance, bbsystem)
{
  _narrowYmax = inputParametersInstance.maxRapidity();
  _narrowYmin = -1.0*_narrowYmax;
  _narrowNumY = inputParametersInstance.nmbRapidityBins();
  _Ep         = inputParametersInstance.protonEnergy(); 
}


//______________________________________________________________________________
narrowResonanceCrossSection::~narrowResonanceCrossSection()
{ }


//______________________________________________________________________________
void
narrowResonanceCrossSection::crossSectionCalculation(const double)  // _bwnormsave (unused)
{
  // This subroutine calculates the vector meson cross section assuming
  // a narrow resonance.  For reference, see STAR Note 386.
  
  double W,dY;
  double y1,y2,y12,ega1,ega2,ega12;
  double csgA1,csgA2,csgA12,int_r,dR;
  double Eth;
  int    J,NY,beam;
  
  NY   =  _narrowNumY;
  dY   = (_narrowYmax-_narrowYmin)/double(NY);
  
  cout<<" Using Narrow Resonance ..."<<endl;
  
  W = getChannelMass();
  Eth=0.5*(((W+protonMass)*(W+protonMass)-
            protonMass*protonMass)/(_Ep+sqrt(_Ep*_Ep-protonMass*protonMass)));
  
  // cout<<" gamma+nuclexon  Threshold: "<<Eth<<endl;
        printf(" gamma+nucleon threshold: %e GeV \n", Eth);

        int A_1 = getbbs().electronBeam().A(); 
        int A_2 = getbbs().targetBeam().A();
  
  int_r=0.;
  
        // Do this first for the case when the first beam is the photon emitter 
        // Treat pA separately with defined beams 
        // The variable beam (=1,2) defines which nucleus is the target 
  for(J=0;J<=(NY-1);J++){
    
    y1  = _narrowYmin + double(J)*dY;
    y2  = _narrowYmin + double(J+1)*dY;
    y12 = 0.5*(y1+y2);
    
                if( A_2 == 1 && A_1 != 1 ){
                  // pA, first beam is the nucleus and is in this case the target  
                  ega1  = 0.5*W*exp(-y1);
                  ega2  = 0.5*W*exp(-y2);
                  ega12 = 0.5*W*exp(-y12);
                  beam = 1; 
                } else if( A_1 ==1 && A_2 != 1){
                  // pA, second beam is the nucleus and is in this case the target 
                  ega1  = 0.5*W*exp(y1);
                  ega2  = 0.5*W*exp(y2);
                  ega12 = 0.5*W*exp(y12);
                  beam = 2; 
                } else {
                  ega1  = 0.5*W*exp(y1);
                  ega2  = 0.5*W*exp(y2);
                  ega12 = 0.5*W*exp(y12);
                  beam = 2; 
                }
    
    if(ega1 < Eth || ega2 < Eth)   
      continue;
    if(ega2 > maxPhotonEnergy() || ega1 > maxPhotonEnergy() ) 
      continue;

    csgA1=getcsgA(ega1,W,beam);
    
    // Middle Point                      =====>>>
    csgA12=getcsgA(ega12,W,beam); 

    // Second Point                      =====>>>
    csgA2=getcsgA(ega2,W,beam);
    
    // Sum the contribution for this W,Y.
    dR  = ega1*photonFlux(ega1,beam)*csgA1;
    dR  = dR + 4.*ega12*photonFlux(ega12,beam)*csgA12;
    dR  = dR + ega2*photonFlux(ega2,beam)*csgA2;
    dR  = dR*(dY/6.);

    // cout<<" y: "<<y12<<" egamma: "<<ega12<<" flux: "<<photonFlux(ega12,beam)<<" sigma_gA: "<<10000000.*csgA12<<" dsig/dy (microb): "<<10000.*dR/dY<<endl;

    int_r = int_r+dR;
  }

        // Repeat the loop for the case when the second beam is the photon emitter. 
        // Don't repeat for pA
        if( !( (A_2 == 1 && A_1 != 1) || (A_1 == 1 && A_2 != 1) ) ){ 
    for(J=0;J<=(NY-1);J++){
    
    y1  = _narrowYmin + double(J)*dY;
    y2  = _narrowYmin + double(J+1)*dY;
    y12 = 0.5*(y1+y2);
    
                beam = 1; 
    ega1  = 0.5*W*exp(-y1);
    ega2  = 0.5*W*exp(-y2);
    ega12 = 0.5*W*exp(-y12);
      
    if(ega2 < Eth || ega1 < Eth)   
      continue;
    if(ega1 > maxPhotonEnergy() || ega2 > maxPhotonEnergy() ) 
      continue;

    csgA1=getcsgA(ega1,W,beam);
    
    // Middle Point                      =====>>>
    csgA12=getcsgA(ega12,W,beam); 

    // Second Point                      =====>>>
    csgA2=getcsgA(ega2,W,beam);
    
    // Sum the contribution for this W,Y.
    dR  = ega1*photonFlux(ega1,beam)*csgA1;
    dR  = dR + 4.*ega12*photonFlux(ega12,beam)*csgA12;
    dR  = dR + ega2*photonFlux(ega2,beam)*csgA2;
    dR  = dR*(dY/6.);

    // cout<<" y: "<<y12<<" egamma: "<<ega12<<" flux: "<<photonFlux(ega12,beam)<<" sigma_gA: "<<10000000.*csgA12<<" dsig/dy (microb): "<<10000.*dR/dY<<endl;

    int_r = int_r+dR;
    }
        }

  cout<<endl;
  if (0.01*int_r > 1.){
    cout<< " Total cross section: "<<0.01*int_r<<" barn."<<endl;
  } else if (10.*int_r > 1.){
    cout<< " Total cross section: " <<10.*int_r<<" mb."<<endl;
        } else if (10000.*int_r > 1.){
    cout<< " Total cross section: " <<10000.*int_r<<" microb."<<endl;
        } else if (10000000.*int_r > 1.){
    cout<< " Total cross section: " <<10000000.*int_r<<" nanob."<<endl;
        } else if (1.E10*int_r > 1.){
    cout<< " Total cross section: "<<1.E10*int_r<<" picob."<<endl;
        } else {
    cout<< " Total cross section: " <<1.E13*int_r<<" femtob."<<endl;
        }
  cout<<endl;
  setPhotonNucleusSigma(0.01*int_r);
}