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Generator.cc
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Generator.cc
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/**************************************************
* This file is a part of the Elegent package:
* http://elegent.hepforge.org/
*************************************************/
#include "interface/Generator.h"
#include "HepMC/GenEvent.h"
#include <cmath>
#include "TGraph.h"
#include "TFile.h"
#include "TClass.h"
#include "TRandom2.h"
using namespace std;
using namespace HepMC;
using namespace Elegent;
//----------------------------------------------------------------------------------------------------
Generator::Generator(const string &_file, const string &_path, double _t_min, double _t_max, unsigned int _verbosity) :
fileName(_file), modelPath(_path), t_min(_t_min), t_max(_t_max), verbosity(_verbosity)
{
}
//----------------------------------------------------------------------------------------------------
unsigned int Generator::Init()
{
// try to open the file
TFile file(fileName.c_str());
if (file.IsZombie())
{
printf("ERROR in Elegent::Generator::Init > File `%s' can not be loaded.\n", fileName.c_str());
return 1;
}
// get cms energy
TGraph *data = (TGraph *) file.Get("data");
if (!data)
{
printf("ERROR in Elegent::Generator::Init > File `%s' does not contain `data' object.\n", fileName.c_str());
return 2;
}
double dummy;
data->GetPoint(0, dummy, E_cms);
// try to load sigma_int graph
TObject *o = file.Get(modelPath.c_str());
if (!o || !o->IsA()->InheritsFrom("TGraph"))
{
file.ls();
printf("ERROR in Elegent::Generator::Init > Model `%s' not found.\n", modelPath.c_str());
return 3;
}
TGraph *sigma_int = (TGraph*) o;
// prepare normalized inverse c.d.f
int i_min = 0, i_max = sigma_int->GetN() - 1; // default index range
for (int i = 0; i < sigma_int->GetN(); i++)
{
double x, y;
sigma_int->GetPoint(i, x, y);
if (x < t_min)
i_min = i;
if (x > t_max)
{
i_max = i;
break;
}
}
double p_min = 0., p_max = 0.;
double t_min_real = 0., t_max_real = 0.;
sigma_int->GetPoint(i_min, t_min_real, p_min);
sigma_int->GetPoint(i_max, t_max_real, p_max);
if (verbosity > 0)
{
printf(">> Elegent::Generator > inverse cdf:\n\tfile: %s\n\tmodel: %s\n", fileName.c_str(), modelPath.c_str());
printf("\trequested |t| range: %.2E to %.2E GeV^2\n", t_min, t_max);
printf("\tpoints loaded: %i\n", i_max - i_min + 1);
printf("\t\tfirst point: idx = %i, |t| = %.2E GeV^2, p = %.2E mb\n", i_min, t_min_real, p_min);
printf("\t\tlast point: idx = %i, |t| = %.2E GeV^2, p = %.2E mb\n", i_max, t_max_real, p_max);
printf("\t|t| range: %.2E to %.2E GeV^2\n", t_min_real, t_max_real);
printf("\tcorresponding cross-section: %.2E mb\n", p_max - p_min);
}
if (i_min >= i_max)
{
printf("ERROR in Elegent::Generator::Init > Wrong (t_min, t_max) region (%.2E, %.2E) or empty intersection with CDF domain.\n", t_min, t_max);
return 4;
}
icdf = new TGraph();
for (int i = i_min; i <= i_max; i++)
{
double x, y;
sigma_int->GetPoint(i, x, y);
icdf->SetPoint(icdf->GetN(), (y - p_min) / (p_max - p_min), x);
}
// precompute kinematics
double m = 0.938; // GeV
p_cms = sqrt(E_cms*E_cms - m*m);
if (verbosity > 0)
{
printf("\n>> Elegent::Generator > proton kinematics in CM frame (in GeV)\n");
printf("\tE = %.3f\n", E_cms);
printf("\tp = %.3f\n", p_cms);
printf("\tm = %.3f\n", m);
}
return 0;
}
//----------------------------------------------------------------------------------------------------
void Generator::GenerateBase(double rn1, double rn2, GenEvent* gEv)
{
gEv->set_signal_process_id(Generator::ElasticScattering);
// create vertex at t = 0, position 0;
GenVertex* gVx = new GenVertex(FourVector(0., 0., 0., 0.));
gEv->add_vertex(gVx);
// generation
double p = 0., t = 0., phi = 0., theta = 0.;
p = rn1;
t = icdf->Eval(p); // |t|
phi = rn2 * 2. * M_PI;
theta = sqrt(t) / p_cms;
// kinematics collison in CM frame
double p_x = p_cms * sin(theta) * cos(phi);
double p_y = p_cms * sin(theta) * sin(phi);
double p_z = p_cms * cos(theta);
if (verbosity > 5)
{
if (verbosity > 6)
printf("prob = %.3f\n", p);
printf("|t| = %.2E GeV^2, theta = %.2E\n", t, theta);
printf("phi = %.2E, theta_x = %.2E, theta_y = %.2E\n", phi, theta*cos(phi), theta*sin(phi));
printf("px = %.2E, py = %.2E, pz = %.2E\n", p_x, p_y, p_z);
}
// add initial and final particles to the vertex
GenParticle* gPe;
gPe = new GenParticle(HepMC::FourVector(0., 0., p_cms, E_cms), PID, NullState); gPe->suggest_barcode(1); gVx->add_particle_in(gPe);
gPe = new GenParticle(HepMC::FourVector(0., 0., -p_cms, E_cms), PID, NullState); gPe->suggest_barcode(2); gVx->add_particle_in(gPe);
gPe = new GenParticle(HepMC::FourVector(p_x, p_y, p_z, E_cms), PID, FinalState); gPe->suggest_barcode(3); gVx->add_particle_out(gPe);
gPe = new GenParticle(HepMC::FourVector(-p_x, -p_y, -p_z, E_cms), PID, FinalState); gPe->suggest_barcode(4); gVx->add_particle_out(gPe);
}
//----------------------------------------------------------------------------------------------------
void Generator::Generate(GenEvent* gEv)
{
GenerateBase(gRandom->Rndm(), gRandom->Rndm(), gEv);
}

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