APFEL: added DIS structure functions modelling

CepGenAddOns/APFELWrapper/CMakeLists.txt

@@ -8,7 +8,9 @@ endif()
 
 #----- build the object
 
-cepgen_build(CepGenAPFEL SOURCES AlphaSAPFEL.cpp APFELCollinearFlux.cpp PartonicStructureFunctionsAPFEL.cpp
+cepgen_build(CepGenAPFEL
+    SOURCES AlphaSAPFEL.cpp APFELCollinearFlux.cpp
+            EvolutionStructureFunctions.cpp PartonicStructureFunctionsAPFEL.cpp
     EXT_LIBS ${APFEL}
     EXT_HEADERS ${APFEL_INCLUDE}
     INSTALL_COMPONENT apfel)

CepGenAddOns/APFELWrapper/EvolutionStructureFunctions.cpp

@@ -0,0 +1,86 @@
+/*
+ *  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 <APFEL/APFEL.h>
+
+#include <cmath>
+
+#include "CepGen/Core/Exception.h"
+#include "CepGen/Modules/StructureFunctionsFactory.h"
+#include "CepGen/Physics/PDG.h"
+#include "CepGen/StructureFunctions/Parameterisation.h"
+
+using namespace std::string_literals;
+
+namespace cepgen {
+  namespace apfel {
+    class EvolutionStructureFunctions final : public strfun::Parameterisation {
+    public:
+      explicit EvolutionStructureFunctions(const ParametersList& params)
+          : strfun::Parameterisation(params),
+            proc_(steer<std::string>("processDIS")),
+            xbj_min_(steer<double>("xBjmin")) {
+        const auto q2range = steer<Limits>("q2range");
+        if (!q2range.valid())
+          throw CG_FATAL("apfel:EvolutionStructureFunctions") << "Invalid Q^2 range: " << q2range << ".";
+        const auto qrange = q2range.compute([](double lim) { return std::sqrt(lim); });
+
+        APFEL::SetMassScheme(steer<std::string>("massScheme"));
+        APFEL::SetProcessDIS(proc_);
+        APFEL::SetQLimits(qrange.min(), qrange.max());
+        APFEL::SetMaxFlavourAlpha(steer<int>("maxFlavourAlpha"));
+        APFEL::SetMaxFlavourPDFs(steer<int>("maxFlavourPDFs"));
+        APFEL::SetPDFSet(steer<std::string>("pdfSet"));
+        APFEL::SetTargetDIS(steer<std::string>("targetDIS"));
+        APFEL::InitializeAPFEL_DIS();
+        APFEL::ComputeStructureFunctionsAPFEL(qrange.min(), qrange.max());
+        APFEL::CacheStructureFunctionsAPFEL(qrange.min());
+      }
+
+      static ParametersDescription description() {
+        auto desc = strfun::Parameterisation::description();
+        desc.setDescription("APFEL DIS structure functions");
+        desc.add("q2range", Limits{1., 1.e6});
+        desc.add<double>("xBjmin", 1.e-6);
+        desc.add("massScheme", "ZM-VFNS"s);
+        desc.add("processDIS", "NC"s);
+        desc.add<int>("maxFlavourAlpha", 5);
+        desc.add<int>("maxFlavourPDFs", 5);
+        desc.add("pdfSet", "CT14nnlo"s);
+        desc.add("targetDIS", "isoscalar"s);
+        return desc;
+      }
+
+    private:
+      void eval() override {
+        if (args_.xbj < xbj_min_) {
+          clear();
+          return;
+        }
+        const auto q = std::sqrt(args_.q2);
+        setF2(APFEL::StructureFunctionxQ(proc_, "F2", "total", args_.xbj, q));
+        setFL(APFEL::StructureFunctionxQ(proc_, "FL", "total", args_.xbj, q));
+      }
+
+      const std::string proc_;
+      const double xbj_min_;
+    };
+  }  // namespace apfel
+}  // namespace cepgen
+using ApfelEvolutionStructureFunctions = cepgen::apfel::EvolutionStructureFunctions;
+REGISTER_STRFUN("apfelEvol", 404, ApfelEvolutionStructureFunctions);