MadGraphProcessImpl.cpp

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/*
 *  CepGen: a central exclusive processes event generator
 *  Copyright (C) 2020-2024  Laurent Forthomme
 *
 *  This program 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
 *  any later version.
 *
 *  This program 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 this program.  If not, see <http://www.gnu.org/licenses/>.
 */
 
//=============================================================================
// NOLI SE TANGERE
#include <iostream>
 
#include "CPPProcess.h"
#include "CepGen/Core/Exception.h"
#include "CepGen/Utils/Caller.h"
#include "CepGen/Utils/Math.h"
#include "CepGenAddOns/MadGraphWrapper/MadGraphProcess.h"
#include "CepGenAddOns/MadGraphWrapper/MadGraphProcessFactory.h"
 
using namespace cepgen;
 
class MadGraphProcessImpl : public MadGraphProcess {
public:
  explicit MadGraphProcessImpl(const ParametersList& params) : MadGraphProcess(params), proc_(new CPPProcess) {
    CG_DEBUG("MadGraphProcessImpl") << "Process considered: " << proc_->name() << ". "
                                    << "Incoming particles: " << incoming_pdgids_
                                    << ", outgoing system: " << central_pdgids_ << ".";
  }
 
  static ParametersDescription description() {
    auto desc = MadGraphProcess::description();
    desc.setDescription("XXX_PROC_DESCRIPTION_XXX");
    desc.add<std::vector<int> >("incomingSystem", {XXX_PART1_XXX, XXX_PART2_XXX});
    desc.add<std::vector<int> >("outgoingSystem", {XXX_OUT_PART_XXX});
    return desc;
  }
 
  void initialise(const std::string& param_card) override {
    try {
      utils::Caller caller;
      proc_->initProc(param_card);
    } catch (const char* chr) {
      throw CG_FATAL("MadGraphProcessImpl:init")
          << "Failed to initialise parameters card at \"" << param_card << "\":\n\t" << chr;
    }
    if (proc_->nprocesses > 1)
      throw CG_FATAL("MadGraphProcessImpl:init") << "Multi-processes matrix elements are not (yet) supported!";
    if (proc_->ninitial != 2)
      throw CG_FATAL("MadGraphProcessImpl:init") << "Currently only 2->N processes are supported!";
 
    CG_DEBUG("MadGraphProcessImpl:init") << "External particles masses (partons + central system): "
                                         << proc_->getMasses() << ".";
 
    mom_.clear();
    for (size_t i = 0; i < proc_->nexternal; ++i)
      mom_.emplace_back(new double[4]{proc_->getMasses().at(i), 0., 0., 0.});
    momenta_.resize(proc_->nexternal);
  }
 
  double eval() override {
    proc_->setMomenta(mom_);
    proc_->sigmaKin();
    const double* me = proc_->getMatrixElements();
    if (!utils::positive(me[0]))
      return 0.;
 
    CG_DEBUG_LOOP("MadGraphProcessImpl:eval").log([&](auto& log) {
      log << "Dump of event kinematics\n\t"
          << "Incoming partons 4-momenta:   " << std::vector<double>(mom_[0], mom_[0] + 4) << ", "
          << std::vector<double>(mom_[1], mom_[1] + 4) << "\n\t"
          << "Outgoing particles 4-momenta: ";
      std::string sep;
      for (size_t i = 0; i < proc_->nexternal - 2; ++i)
        log << sep << std::vector<double>(mom_[i + 2], mom_[i + 2] + 4), sep = ", ";
      log << "\n\tResulting matrix element: " << me[0] << ".";
    });
    return me[0];
  }
 
  const std::vector<Momentum>& momenta() override {
    const auto& p4 = proc_->getMomenta();
    // cast it to the member attribute and return it
    for (size_t i = 0; i < p4.size(); ++i)
      momenta_[i] = Momentum::fromPxPyPzE(p4[i][1], p4[i][2], p4[i][3], p4[i][0]);
    return momenta_;
  }
 
private:
  const std::unique_ptr<CPPProcess> proc_;
  std::vector<Momentum> momenta_;
};
REGISTER_MG5AMC_PROCESS("XXX_PROC_NAME_XXX", MadGraphProcessImpl);
//=============================================================================