StructureFunctions.cpp

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/*
 *  CepGen: a central exclusive processes event generator
 *  Copyright (C) 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/>.
 */
 
#include "CepGen/Modules/StructureFunctionsFactory.h"
#include "CepGen/StructureFunctions/Parameterisation.h"
#include "CepGen/Utils/Message.h"
#include "CepGenAddOns/Herwig6Wrapper/Herwig6Interface.h"
 
namespace cepgen {
  namespace herwig6 {
    class StructureFunctions final : public strfun::Parameterisation {
    public:
      explicit StructureFunctions(const ParametersList& params)
          : strfun::Parameterisation(params), idhad_(steer<int>("idhad")), nset_(steer<int>("nset")) {}
 
      static ParametersDescription description() {
        initialise();
        auto desc = strfun::Parameterisation::description();
        desc.setDescription("Herwig 6 structure functions evaluator");
        desc.add<int>("idhad", 73)
            .setDescription("type of hadron")
            .allow(30, "pi-")
            .allow(38, "pi+")
            .allow(59, "photon")
            .allow(73, "proton")
            .allow(75, "neutron")
            .allow(91, "antiproton")
            .allow(93, "antineutron");
        desc.add<int>("nset", 8)
            .setDescription("structure functions set")
            .allow(1, "Duke & Owens set 1 (for soft/hard glue)")
            .allow(2, "Duke & Owens set 2 (for soft/hard glue)")
            .allow(3, "Eichten & al. set 1 (nucleons only)")
            .allow(4, "Eichten & al. set 2 (nucleons only)")
            .allow(5, "Owens set 1.1")
            .allow(6, "MRST98LO (central alpha(S)/gluon)")
            .allow(7, "MRST98LO (higher gluon)")
            .allow(8, "MRST98LO (average of central and higher gluon)");
        return desc;
      }
 
    private:
      void eval() override { setF2(hwsfun(args_.xbj, args_.q2, idhad_, nset_, 2)); }
      const int idhad_, nset_;
    };
  }  // namespace herwig6
}  // namespace cepgen
using Herwig6StructureFunctions = cepgen::herwig6::StructureFunctions;
REGISTER_STRFUN("herwig6", 403, Herwig6StructureFunctions);