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	diff --git a/.clang-format b/.clang-format
	--- a/.clang-format
	+++ b/.clang-format
	@@ -66,7 +66,7 @@
	Priority: 4
	- Regex: '^"(HepMC\|HepMC3)/'
	Priority: 5
	- - Regex: '^"(Pythia8\|Photos\|Tauola)/'
	+ - Regex: '^"(Pythia8\|Photos\|Tauola\|SHERPA\|ATOOLS)/'
	Priority: 6
	- Regex: '^"T[[:alnum:]]+\.h"'
	Priority: 7
	diff --git a/.gitlab-ci.yml b/.gitlab-ci.yml
	--- a/.gitlab-ci.yml
	+++ b/.gitlab-ci.yml
	@@ -14,6 +14,7 @@
	USE_PYTHIA: "ON"
	USE_PHOTOS: "ON"
	USE_TAUOLA: "ON"
	+ USE_SHERPA: "ON"

	.future_os_image:
	variables:
	@@ -49,7 +50,7 @@
	script:
	- mkdir install
	- mkdir build && cd build
	- - cmake -DCMAKE_BUILD_TYPE:STRING=$BUILD_TYPE -DCMAKE_INSTALL_PREFIX:PATH=$CI_PROJECT_DIR/install -DEVTGEN_HEPMC3:BOOL=$USE_HEPMC3 -DEVTGEN_PYTHIA:BOOL=$USE_PYTHIA -DEVTGEN_PHOTOS:BOOL=$USE_PHOTOS -DEVTGEN_TAUOLA:BOOL=$USE_TAUOLA -DEVTGEN_BUILD_TESTS:BOOL=$BUILD_TESTS -DEVTGEN_BUILD_VALIDATIONS:BOOL=$BUILD_TESTS -DEVTGEN_BUILD_DOXYGEN:BOOL=$BUILD_DOXYGEN $CI_PROJECT_DIR
	+ - cmake -DCMAKE_BUILD_TYPE:STRING=$BUILD_TYPE -DCMAKE_INSTALL_PREFIX:PATH=$CI_PROJECT_DIR/install -DEVTGEN_HEPMC3:BOOL=$USE_HEPMC3 -DEVTGEN_PYTHIA:BOOL=$USE_PYTHIA -DEVTGEN_PHOTOS:BOOL=$USE_PHOTOS -DEVTGEN_TAUOLA:BOOL=$USE_TAUOLA -DEVTGEN_SHERPA:BOOL=$USE_SHERPA -DEVTGEN_BUILD_TESTS:BOOL=$BUILD_TESTS -DEVTGEN_BUILD_VALIDATIONS:BOOL=$BUILD_TESTS -DEVTGEN_BUILD_DOXYGEN:BOOL=$BUILD_DOXYGEN $CI_PROJECT_DIR
	- cmake --build .
	- cmake --build . --target install

	@@ -82,7 +83,7 @@
	- .check_template
	script:
	- mkdir build && cd build
	- - cmake -DEVTGEN_HEPMC3:BOOL=ON -DEVTGEN_PYTHIA:BOOL=ON -DEVTGEN_PHOTOS:BOOL=ON -DEVTGEN_TAUOLA:BOOL=ON -DEVTGEN_BUILD_TESTS:BOOL=OFF -DEVTGEN_BUILD_DOXYGEN:BOOL=ON $CI_PROJECT_DIR
	+ - cmake -DEVTGEN_HEPMC3:BOOL=ON -DEVTGEN_PYTHIA:BOOL=ON -DEVTGEN_PHOTOS:BOOL=ON -DEVTGEN_TAUOLA:BOOL=ON -DEVTGEN_SHERPA:BOOL=ON -DEVTGEN_BUILD_TESTS:BOOL=OFF -DEVTGEN_BUILD_DOXYGEN:BOOL=ON $CI_PROJECT_DIR
	- cmake --build . --target doc
	- curl -o renameMemberVars.py "https://gitlab.cern.ch/evtgen/utilities/raw/master/RenameMemberVars/renameMemberVars.py?inline=false"
	- python renameMemberVars.py check $CI_PROJECT_DIR doxygen/html
	@@ -106,6 +107,7 @@
	LCG_VERSION: "LCG_103_LHCB_7"
	LCG_COMPILER: "gcc$GCC_VERSION-opt"
	USE_HEPMC3: "OFF"
	+ USE_SHERPA: "OFF"
	extends:
	- .production_image
	- .build_template
	diff --git a/CMakeLists.txt b/CMakeLists.txt
	--- a/CMakeLists.txt
	+++ b/CMakeLists.txt
	@@ -64,6 +64,7 @@
	option(EVTGEN_PYTHIA "Enable/disable linking with Pythia8" OFF)
	option(EVTGEN_PHOTOS "Enable/disable linking with Photos++" OFF)
	option(EVTGEN_TAUOLA "Enable/disable linking with Tauola++" OFF)
	+option(EVTGEN_SHERPA "Enable/disable linking with Sherpa" OFF)
	option(EVTGEN_SUPPRESS_EXTERNAL_WARNINGS "Enable/disable suppression of warnings from external dependencies" OFF)
	if (EVTGEN_HEPMC3)
	message(STATUS "EvtGen: Linking with HepMC3")
	@@ -74,6 +75,7 @@
	message(STATUS "EvtGen: Optional linking with Pythia8 EVTGEN_PYTHIA ${EVTGEN_PYTHIA}")
	message(STATUS "EvtGen: Optional linking with Photos++ EVTGEN_PHOTOS ${EVTGEN_PHOTOS}")
	message(STATUS "EvtGen: Optional linking with Tauola++ EVTGEN_TAUOLA ${EVTGEN_TAUOLA}")
	+message(STATUS "EvtGen: Optional linking with Sherpa EVTGEN_SHERPA ${EVTGEN_SHERPA}")
	include(EvtGenExternalDependencies)

	# Setup clang-tidy checks
	diff --git a/EvtGenExternal/EvtExternalGenList.hh b/EvtGenExternal/EvtExternalGenList.hh
	--- a/EvtGenExternal/EvtExternalGenList.hh
	+++ b/EvtGenExternal/EvtExternalGenList.hh
	@@ -43,6 +43,10 @@
	EvtAbsRadCorr* getPhotosModel( const double infraredCutOff = 1.0e-7,
	const double maxWtInterference = 64.0 );

	+ EvtAbsRadCorr* getSherpaPhotonsModel( const double infraredCutOff = 1.0e-7,
	+ const int mode = 2,
	+ const int useME = 0 );
	+
	protected:
	private:
	std::string m_photonType;
	diff --git a/EvtGenExternal/EvtSherpaPhotons.hh b/EvtGenExternal/EvtSherpaPhotons.hh
	new file mode 100644
	--- /dev/null
	+++ b/EvtGenExternal/EvtSherpaPhotons.hh
	@@ -0,0 +1,86 @@
	+
	+/***********************************************************************
	+* Copyright 1998-2020 CERN for the benefit of the EvtGen authors *
	+* *
	+* This file is part of EvtGen. *
	+* *
	+* EvtGen 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. *
	+* *
	+* EvtGen 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 EvtGen. If not, see <https://www.gnu.org/licenses/>. *
	+***********************************************************************/
	+
	+#ifdef EVTGEN_SHERPA
	+#ifndef EVTSHERPAPHOTONS_HH
	+#define EVTSHERPAPHOTONS_HH
	+
	+#include "EvtGenBase/EvtAbsRadCorr.hh"
	+#include "EvtGenBase/EvtHepMCEvent.hh"
	+#include "EvtGenBase/EvtId.hh"
	+#include "EvtGenBase/EvtPDL.hh"
	+#include "EvtGenBase/EvtParticle.hh"
	+
	+#include "SHERPA/Main/Sherpa.H"
	+
	+#include <string>
	+
	+class EvtParticle;
	+class EvtAbsExternalGen;
	+
	+/* Description: EvtGen's interface to PHOTOS for generation of
	+ * QED final state radiation.
	+ */
	+class EvtSherpaPhotons : public EvtAbsRadCorr {
	+ public:
	+ EvtSherpaPhotons( const bool useEvtGenRandom = true,
	+ const double infraredCutOff = 1.0e-7, const int mode = 2,
	+ const int useME = 0 );
	+
	+ void initialise() override;
	+
	+ void doRadCorr( EvtParticle* p ) override;
	+
	+ private:
	+ // Provides vector of pointers to the configuration strings for Sherpa
	+ std::vector<char*> addParameters();
	+
	+ // Updates the particle properties table of Sherpa
	+ void updateParticleLists();
	+
	+ // The Sherpa instance.
	+ std::unique_ptr<SHERPA::Sherpa> m_sherpaGen;
	+
	+ // Vector containing the configuration strings for Sherpa
	+ // INIT_ONLY=6 intialises the Sherpa objects without launching simulation.
	+ std::vector<std::string> m_configs{ "Sherpa", "INIT_ONLY=6" };
	+
	+ // Use EvtGen's random number generator
	+ bool m_useEvtGenRandom = true;
	+
	+ // Default settings for PHOTONS++
	+ // Minimum photon Energy (infrared cut-off).
	+ double m_infraredCutOff = 1.0e-7;
	+ // Switches on (default) the hard emission corrections (mode 2),
	+ // otherwise follow the soft-photon only approach (mode 1).
	+ int m_mode = 2;
	+ // Switches off (default) or on the exact matrix-element corrections (works only for mode 2)
	+ int m_useME = 0;
	+
	+ // Default photon properties
	+ const std::string m_photonType = "gamma";
	+ EvtId m_gammaId = EvtId( -1, -1 );
	+ long int m_gammaPDG = 22;
	+ bool m_initialised = false;
	+};
	+
	+#endif
	+
	+#endif
	diff --git a/EvtGenExternal/EvtSherpaRandom.hh b/EvtGenExternal/EvtSherpaRandom.hh
	new file mode 100644
	--- /dev/null
	+++ b/EvtGenExternal/EvtSherpaRandom.hh
	@@ -0,0 +1,94 @@
	+
	+/***********************************************************************
	+* Copyright 1998-2020 CERN for the benefit of the EvtGen authors *
	+* *
	+* This file is part of EvtGen. *
	+* *
	+* EvtGen 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. *
	+* *
	+* EvtGen 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 EvtGen. If not, see <https://www.gnu.org/licenses/>. *
	+***********************************************************************/
	+
	+#ifdef EVTGEN_SHERPA
	+
	+#ifndef EVTSHERPARANDOM_HH
	+#define EVTSHERPARANDOM_HH
	+
	+#include "EvtGenBase/EvtRandom.hh"
	+
	+#include "ATOOLS/Math/Random.H"
	+
	+/* Description: Class to specify the chosen EvtGen random number (engine)
	+ * to be used for Sherpa.
	+ */
	+
	+class EvtSherpaRandom : public ATOOLS::External_RNG {
	+ public:
	+ double Get() { return EvtRandom::Flat(); }
	+
	+ private:
	+};
	+
	+// The following code makes EvtSherpaRandom loadable in Sherpa
	+
	+//! \cond DOXYGEN_IGNORE
	+
	+// In Sherpa versions v2.2.15 and earlier the DECLARE_GETTER macro produces code that doesn't compile with gcc versions > 12 and C++20
	+// So, in those cases, instead use explicit code that has been modified to work correctly
	+#ifdef EVTGEN_SHERPA_USEMACRO
	+DECLARE_GETTER( EvtSherpaRandom, "EvtSherpaRandom", ATOOLS::External_RNG,
	+ ATOOLS::RNG_Key );
	+#else
	+namespace ATOOLS {
	+ template <>
	+ class Getter<External_RNG, RNG_Key, EvtSherpaRandom> :
	+ public Getter_Function<External_RNG, RNG_Key> {
	+ public:
	+ Getter( const bool& d = true ) :
	+ Getter_Function<External_RNG, RNG_Key>{ "EvtSherpaRandom" }
	+ {
	+ SetDisplay( d );
	+ }
	+
	+ protected:
	+ void PrintInfo( std::ostream& str, const size_t width ) const;
	+ Object_Type* operator()( const Parameter_Type& parameters ) const;
	+
	+ private:
	+ static Getter<External_RNG, RNG_Key, EvtSherpaRandom> s_initializer;
	+ };
	+} // namespace ATOOLS
	+
	+ATOOLS::Getter<ATOOLS::External_RNG, ATOOLS::RNG_Key, EvtSherpaRandom>
	+ ATOOLS::Getter<ATOOLS::External_RNG, ATOOLS::RNG_Key, EvtSherpaRandom>::s_initializer{
	+ true };
	+#endif
	+
	+ATOOLS::External_RNG*
	+ATOOLS::Getter<ATOOLS::External_RNG, ATOOLS::RNG_Key, EvtSherpaRandom>::operator()(
	+ const ATOOLS::RNG_Key& ) const
	+{
	+ return new EvtSherpaRandom();
	+}
	+
	+// This eventually prints a help message
	+void ATOOLS::Getter<ATOOLS::External_RNG, ATOOLS::RNG_Key, EvtSherpaRandom>::PrintInfo(
	+ std::ostream& str, const size_t ) const
	+{
	+ str << " EvtGen-Sherpa RNG interface";
	+}
	+
	+//! \endcond
	+
	+#endif
	+
	+#endif
	diff --git a/History.md b/History.md
	--- a/History.md
	+++ b/History.md
	@@ -11,8 +11,16 @@
	===
	## R02-0X-00

	+21 May 2024 Fernando Abudinen
	+* D115: Introduced Sherpa's PHOTONS++ generator
	+ as alternative for final-state radiation simulation.
	+ - Added Sherpa dependencies and linking in compilation files
	+ - Introduced new `EvtSherpaPhotons` interface
	+ - Introduced new `EvtSherpaRandom` interface to propagate EvtGen's random number into Sherpa
	+ - Implemented `fsrGenerator` as input argument in `testDecayModel` module
	+
	8 May 2024 Michal Kreps, Thomas Latham, Andrii Verbytskyi
	-* D58: Rename member variables to follow convention of m_ prefix
	+* D58: Rename member variables to follow convention of `m_` prefix
	- In addition:
	* Introduce pre-build check in the CI that convention is being followed in all classes
	* Fix shadowing of variables in some classes
	diff --git a/README.md b/README.md
	--- a/README.md
	+++ b/README.md
	@@ -23,14 +23,16 @@
	We now recommend using HepMC3 but support for HepMC2 continues to be available.

	Optionally, it is possible to use other external generators, such as Pythia8
	-(for Pythia decays in the DECAY.DEC file, for example), Photos (for
	-radiative corrections) and Tauola (for tau decays):
	+(for Pythia decays in the DECAY.DEC file, for example), Photos or Sherpa's Photons++
	+(for radiative corrections) and Tauola (for tau decays):

	Pythia8 https://pythia.org/

	-Photos http://photospp.web.cern.ch/photospp/
	+Photos https://photospp.web.cern.ch/

	-Tauola http://tauolapp.web.cern.ch/tauolapp/
	+Tauola https://tauolapp.web.cern.ch/
	+
	+Sherpa https://sherpa-team.gitlab.io/

	All of these packages have instructions for building them.

	@@ -38,6 +40,7 @@
	Pythia8: 8.201 or newer
	Photos: 3.64 or newer
	Tauola: 1.1.8 or newer
	+Sherpa: 2.0.0 or newer

	Once these packages are available, build the EvtGen release by creating a build directory
	alongside the EvtGen source directory (assumed here to be called evtgen.git) and running:
	@@ -88,6 +91,13 @@
	depending on your build environment, otherwise the
	location can be specified via this option.

	+ `-DEVTGEN_SHERPA=ON` : Enable linking with Sherpa (OFF by default)
	+
	+ `-DSHERPA_ROOT_DIR=<location>` : Location of Sherpa install directory
	+ As with HepMC this may be automatically detected
	+ depending on your build environment, otherwise the
	+ location can be specified via this option.
	+
	`-DEVTGEN_BUILD_DOC=ON` : Enable building documentation in 'doc' directory (OFF by default)

	`-DEVTGEN_BUILD_TESTS=ON` : Enable building executables in 'test' directory (OFF by default)
	@@ -168,23 +178,26 @@

	To use the external generators, use the following code:
	```c++
	- #include "EvtGenExternal/EvtExternalGenList.hh"
	#include "EvtGenBase/EvtAbsRadCorr.hh"
	#include "EvtGenBase/EvtDecayBase.hh"

	+ #include "EvtGenExternal/EvtExternalGenList.hh"
	+
	// Set up the default external generator list: Photos, Pythia and/or Tauola
	EvtExternalGenList genList;
	EvtAbsRadCorr* radCorrEngine = genList.getPhotosModel();
	std::list<EvtDecayBase*> extraModels = genList.getListOfModels();

	// Create the EvtGen generator object
	- EvtGen myGenerator("decayFile.dec", "evt.pdl", randomEnginePointer,
	- radCorrEngine, &extraModels);
	+ EvtGen myGenerator( "decayFile.dec", "evt.pdl", randomEnginePointer,
	+ radCorrEngine, &extraModels );

	//If you don't want to use external generators, use the following:
	//EvtGen myGenerator("decayFile.dec", "evt.pdl", randomEnginePointer);
	```

	+ To use Sherpa's PHOTONS++ generator instead of Photos, replace above `getPhotosModel()` with `getSherpaPhotonsModel()`.
	+
	The files [Pythia8_README.md](Pythia8_README.md) and [Tauola_README.md](Tauola_README.md) have more details about
	using the new Pythia 8 and Tauola generators (called via the PYTHIA and TAUOLA
	"decay.dec" model names). The new Photos generator is still called via the PHOTOS
	@@ -193,7 +206,7 @@
	It is now possible to use alias particle decays for the Pythia 8 model.
	Two Pythia 8 instances are used in EvtPythiaEngine for normal and aliased decays.
	Since the underlying code for Photos and Tauola is still Fortran, it is only
	- possible to have one (unique) instance of each of these external generators.
	+ possible to have one unique instance of each of these external generators.
	This can only be fixed if these packages are converted to pure C++ code.


	@@ -206,7 +219,6 @@
	(EvtGenModels/EvtGenericDalitz.cpp), that should be used instead of EvtDDalitz.
	The generic Dalitz model uses xml files to configure the resonance amplitude
	parameters (instead of being hardcoded in EvtDDalitz):
	-
	```
	Decay D+
	1.0 K- pi+ pi+ GENERIC_DALITZ MyDalitzParameters.xml;
	@@ -229,5 +241,3 @@
	One or the other can be chosen as the mixing method for the B system by
	choosing 0 (coherent) or 1 (incoherent) for the last integer argument
	in the EvtGen() constructor.
	-
	-
	diff --git a/cmake/Modules/EvtGenCompilerFlags.cmake b/cmake/Modules/EvtGenCompilerFlags.cmake
	--- a/cmake/Modules/EvtGenCompilerFlags.cmake
	+++ b/cmake/Modules/EvtGenCompilerFlags.cmake
	@@ -35,6 +35,8 @@
	set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -fsigned-char -Wall -Wextra -Wshadow -Woverloaded-virtual")

	if( ${CMAKE_CXX_COMPILER_ID} STREQUAL "GNU" )
	+ # Save temporary intermediate compilation products, e.g. result of pre-processor, etc.
	+ #set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -save-temps=obj")
	set(CMAKE_CXX_FLAGS_DEBUG "-Og -g3")
	set(CMAKE_CXX_FLAGS_MINSIZEREL "-Os -DNDEBUG")
	set(CMAKE_CXX_FLAGS_RELEASE "-O3 -DNDEBUG")
	diff --git a/cmake/Modules/EvtGenExternalDependencies.cmake b/cmake/Modules/EvtGenExternalDependencies.cmake
	--- a/cmake/Modules/EvtGenExternalDependencies.cmake
	+++ b/cmake/Modules/EvtGenExternalDependencies.cmake
	@@ -27,6 +27,7 @@
	set(Tauola++_ROOT_DIR "${CMAKE_INSTALL_PREFIX}" CACHE PATH "Location of Tauola++ installation")
	set(PHOTOSPP_ROOT_DIR "${CMAKE_INSTALL_PREFIX}" CACHE PATH "Location of Photos++ installation - alternative spelling")
	set(TAUOLAPP_ROOT_DIR "${CMAKE_INSTALL_PREFIX}" CACHE PATH "Location of Tauola++ installation - alternative spelling")
	+set(SHERPA_ROOT_DIR "${CMAKE_INSTALL_PREFIX}" CACHE PATH "Location of Sherpa installation")

	# The components we search for in the external generators depend on the version
	# of HepMC we're working with
	@@ -43,6 +44,9 @@
	# From version 1.1.8 Tauola has HepMC3 support
	find_package(Tauola++ REQUIRED COMPONENTS Fortran CxxInterface HepMC3)
	endif()
	+ if(EVTGEN_SHERPA)
	+ find_package(Sherpa 2.0.0 REQUIRED)
	+ endif()
	else()
	find_package(HepMC2 REQUIRED)
	if(EVTGEN_PYTHIA)
	@@ -57,4 +61,7 @@
	# Older versions of Tauola don't have the HepMC component, the HepMC2 interface is in CxxInterface
	find_package(Tauola++ REQUIRED COMPONENTS Fortran CxxInterface OPTIONAL_COMPONENTS HepMC)
	endif()
	+ if(EVTGEN_SHERPA)
	+ find_package(Sherpa 2.0.0 REQUIRED)
	+ endif()
	endif()
	diff --git a/cmake/Modules/FindPythia8.cmake b/cmake/Modules/FindPythia8.cmake
	--- a/cmake/Modules/FindPythia8.cmake
	+++ b/cmake/Modules/FindPythia8.cmake
	@@ -41,7 +41,7 @@
	if(PYTHIA8_XML AND NOT PYTHIA8_VERSION)
	file(READ ${PYTHIA8_XML}/Version.xml versionstr)
	string(REGEX REPLACE ".Pythia:versionNumber.default.[0-9][.]([0-9]+)." "\\1" PYTHIA8_VERSION "${versionstr}")
	- set(PYTHIA8_VERSION ${PYTHIA8_VERSION} CACHE STRING "Detected version of Pythia8.")
	+ set(PYTHIA8_VERSION ${PYTHIA8_VERSION} CACHE STRING "Detected version of Pythia8")
	mark_as_advanced(PYTHIA8_VERSION)
	endif()

	@@ -76,7 +76,7 @@
	# handle the QUIETLY and REQUIRED arguments and set PYTHIA8_FOUND to TRUE if
	# all listed variables are TRUE
	include(FindPackageHandleStandardArgs)
	-FIND_PACKAGE_HANDLE_STANDARD_ARGS(Pythia8 DEFAULT_MSG PYTHIA8_INCLUDE_DIR PYTHIA8_LIBRARIES PYTHIA8_XML)
	+FIND_PACKAGE_HANDLE_STANDARD_ARGS(Pythia8 DEFAULT_MSG PYTHIA8_VERSION PYTHIA8_INCLUDE_DIR PYTHIA8_LIBRARIES PYTHIA8_XML)

	set(PYTHIA8_INCLUDE_DIRS ${PYTHIA8_INCLUDE_DIR})

	diff --git a/cmake/Modules/FindSherpa.cmake b/cmake/Modules/FindSherpa.cmake
	new file mode 100644
	--- /dev/null
	+++ b/cmake/Modules/FindSherpa.cmake
	@@ -0,0 +1,81 @@
	+
	+########################################################################
	+# Copyright 1998-2020 CERN for the benefit of the EvtGen authors #
	+# #
	+# This file is part of EvtGen. #
	+# #
	+# EvtGen 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. #
	+# #
	+# EvtGen 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 EvtGen. If not, see <https://www.gnu.org/licenses/>. #
	+########################################################################
	+
	+# - Try to find Sherpa
	+# Defines:
	+#
	+# SHERPA_FOUND
	+# SHERPA_VERSION
	+# SHERPA_INCLUDE_DIR
	+# SHERPA_INCLUDE_DIRS (not cached)
	+# SHERPA_LIBRARY
	+# SHERPA_LIBRARIES (not cached)
	+# SHERPA_LIBRARY_DIRS (not cached)
	+
	+find_path(SHERPA_INCLUDE_DIR SHERPA/Main/Sherpa.H
	+ HINTS $ENV{SHERPA_ROOT_DIR}/include ${SHERPA_ROOT_DIR}/include
	+ PATH_SUFFIXES include SHERPA-MC)
	+
	+mark_as_advanced(SHERPA_INCLUDE_DIR)
	+
	+# Enforce a minimal list if none is explicitly requested
	+if(NOT Sherpa_FIND_COMPONENTS)
	+ set(Sherpa_FIND_COMPONENTS SherpaMain ModelMain METoolsMain METoolsLoops METoolsSpinCorrelations PDF PhotonsMEs PhotonsMain PhotonsPhaseSpace PhotonsTools Remnant ToolsMath ToolsOrg ToolsPhys)
	+endif()
	+
	+foreach(component ${Sherpa_FIND_COMPONENTS})
	+ find_library(SHERPA_${component}_LIBRARY NAMES ${component} ${_${component}_names}
	+ HINTS $ENV{SHERPA_ROOT_DIR}/lib ${SHERPA_ROOT_DIR}/lib $ENV{SHERPA_ROOT_DIR}/lib64 ${SHERPA_ROOT_DIR}/lib64
	+ PATH_SUFFIXES SHERPA-MC)
	+ if (SHERPA_${component}_LIBRARY)
	+ set(SHERPA_${component}_FOUND 1)
	+ list(APPEND SHERPA_LIBRARIES ${SHERPA_${component}_LIBRARY})
	+
	+ get_filename_component(libdir ${SHERPA_${component}_LIBRARY} PATH)
	+ list(APPEND SHERPA_LIBRARY_DIRS ${libdir})
	+ else()
	+ set(SHERPA_${component}_FOUND 0)
	+ endif()
	+ mark_as_advanced(SHERPA_${component}_LIBRARY)
	+endforeach()
	+
	+if(SHERPA_LIBRARY_DIRS)
	+ list(REMOVE_DUPLICATES SHERPA_LIBRARY_DIRS)
	+endif()
	+
	+find_program(SHERPA_CONFIG Sherpa-config
	+ HINTS $ENV{SHERPA_ROOT_DIR}/bin ${SHERPA_ROOT_DIR}/bin)
	+
	+if(SHERPA_CONFIG)
	+ execute_process(COMMAND ${SHERPA_CONFIG} --version
	+ OUTPUT_VARIABLE SHERPA_VERSION
	+ OUTPUT_STRIP_TRAILING_WHITESPACE)
	+ set(SHERPA_VERSION ${SHERPA_VERSION} CACHE STRING "Detected version of Sherpa")
	+ mark_as_advanced(SHERPA_VERSION)
	+endif()
	+
	+# handle the QUIETLY and REQUIRED arguments and set SHERPA_FOUND to TRUE if
	+# all listed variables are TRUE
	+include(FindPackageHandleStandardArgs)
	+FIND_PACKAGE_HANDLE_STANDARD_ARGS(Sherpa DEFAULT_MSG SHERPA_VERSION SHERPA_INCLUDE_DIR SHERPA_LIBRARIES )
	+
	+set(SHERPA_INCLUDE_DIRS ${SHERPA_INCLUDE_DIR})
	+
	+mark_as_advanced(SHERPA_FOUND)
	diff --git a/doxygen/Doxyfile.in b/doxygen/Doxyfile.in
	--- a/doxygen/Doxyfile.in
	+++ b/doxygen/Doxyfile.in
	@@ -2059,7 +2059,7 @@
	# recursively expanded use the := operator instead of the = operator.
	# This tag requires that the tag ENABLE_PREPROCESSING is set to YES.

	-PREDEFINED = EVTGEN_HEPMC3 EVTGEN_PYTHIA EVTGEN_PHOTOS EVTGEN_TAUOLA
	+PREDEFINED = EVTGEN_HEPMC3 EVTGEN_PYTHIA EVTGEN_PHOTOS EVTGEN_TAUOLA EVTGEN_SHERPA

	# If the MACRO_EXPANSION and EXPAND_ONLY_PREDEF tags are set to YES then this
	# tag can be used to specify a list of macro names that should be expanded. The
	diff --git a/setupEvtGen.sh b/setupEvtGen.sh
	--- a/setupEvtGen.sh
	+++ b/setupEvtGen.sh
	@@ -41,35 +41,64 @@
	# Location in which to install
	INSTALL_PREFIX="/usr/local"

	-# EvtGen version or tag number (or branch name). No extra spaces on this line!
	-VERSION=R02-02-00
	+# EvtGen version or tag number (or branch name)
	+VERSION="R02-02-00"
	+
	+# EvtGen git URL
	+# HepForge main repo
	+EVTGEN_URL="https://phab.hepforge.org/source/evtgen.git"
	+# CERN GitLab mirror
	+#EVTGEN_URL="https://gitlab.cern.ch/evtgen/evtgen.git"
	+
	+# Options to pass to 'make', e.g. "-j 6"
	+BUILDARGS=""

	# HepMC version numbers - change HEPMCMAJORVERSION to 2 in order to use HepMC2
	HEPMCMAJORVERSION="3"
	HEPMC2VER="2.06.10"
	HEPMC3VER="3.2.6"
	-HEPMC2PKG="HepMC-"$HEPMC2VER
	-HEPMC3PKG="HepMC3-"$HEPMC3VER
	-HEPMC2TAR="hepmc"$HEPMC2VER".tgz"
	-HEPMC3TAR=$HEPMC3PKG".tar.gz"
	+HEPMC2PKG="HepMC-$HEPMC2VER"
	+HEPMC3PKG="HepMC3-$HEPMC3VER"
	+HEPMC2TAR="hepmc$HEPMC2VER.tgz"
	+HEPMC3TAR="$HEPMC3PKG.tar.gz"
	+HEPMCBASEURL="http://hepmc.web.cern.ch/hepmc/releases"
	+if [ "$HEPMCMAJORVERSION" -lt "3" ]
	+then
	+ HEPMCURL=$HEPMCBASEURL/$HEPMC2TAR
	+else
	+ HEPMCURL=$HEPMCBASEURL/$HEPMC3TAR
	+fi

	-# Pythia version number with no decimal points, e.g. 8230 corresponds to version 8.230. This
	-# follows the naming convention of Pythia install tar files. Again, no extra spaces allowed.
	-PYTHIAVER=8310
	-PYTHIAPKG="pythia"$PYTHIAVER
	-PYTHIATAR=$PYTHIAPKG".tgz"
	+# Pythia version number with no decimal points, e.g. 8310 corresponds to version 8.310
	+# This follows the naming convention of Pythia install tar files
	+PYTHIAVER="8310"
	+PYTHIAPKG="pythia$PYTHIAVER"
	+PYTHIATAR="$PYTHIAPKG.tgz"
	+PYTHIABASEURL="https://pythia.org/download"
	+PYTHIAURL="$PYTHIABASEURL/pythia${PYTHIAVER:0:2}/$PYTHIATAR"

	# Photos++ version number
	PHOTOSVER="3.64"
	PHOTOSPKG="PHOTOS"
	-PHOTOSDIR="PHOTOS."$PHOTOSVER
	-PHOTOSTAR=$PHOTOSDIR".tar.gz"
	+PHOTOSDIR="PHOTOS.$PHOTOSVER"
	+PHOTOSTAR="$PHOTOSDIR.tar.gz"
	+PHOTOSBASEURL="https://photospp.web.cern.ch/resources"
	+PHOTOSURL="$PHOTOSBASEURL/$PHOTOSDIR/$PHOTOSTAR"

	# Tauola++ version number
	TAUOLAVER="1.1.8"
	TAUOLAPKG="TAUOLA"
	-TAUOLADIR="TAUOLA."$TAUOLAVER
	-TAUOLATAR=$TAUOLADIR".tar.gz"
	+TAUOLADIR="TAUOLA.$TAUOLAVER"
	+TAUOLATAR="$TAUOLADIR.tar.gz"
	+TAUOLABASEURL="https://tauolapp.web.cern.ch/resources"
	+TAUOLAURL="$TAUOLABASEURL/$TAUOLADIR/$TAUOLATAR"
	+
	+# Sherpa version number
	+SHERPAVER="2.2.15"
	+SHERPAPKG="sherpa-v$SHERPAVER"
	+SHERPATAR="$SHERPAPKG.tar.gz"
	+SHERPABASEURL="https://gitlab.com/sherpa-team/sherpa/-/archive"
	+SHERPAURL="$SHERPABASEURL/v$SHERPAVER/$SHERPATAR"

	# Determine OS
	osArch=`uname`
	@@ -106,10 +135,10 @@
	mkdir -p sources
	mkdir -p builds

	-echo Downloading EvtGen source from GIT
	+echo Downloading EvtGen source from GIT, using URL: $EVTGEN_URL

	cd sources
	-git clone https://phab.hepforge.org/source/evtgen.git evtgen
	+git clone $EVTGEN_URL evtgen
	cd evtgen
	git checkout $VERSION

	@@ -123,15 +152,16 @@
	export LC_ALL=en_US.UTF-8
	fi

	-if [ "$HEPMCMAJORVERSION" -lt "3" ]
	-then
	- curl -O http://hepmc.web.cern.ch/hepmc/releases/$HEPMC2TAR
	-else
	- curl -O http://hepmc.web.cern.ch/hepmc/releases/$HEPMC3TAR
	-fi
	-curl -O https://pythia.org/download/pythia${PYTHIAVER:0:2}/$PYTHIATAR
	-curl -O http://photospp.web.cern.ch/photospp/resources/$PHOTOSDIR/$PHOTOSTAR
	-curl -O http://tauolapp.web.cern.ch/tauolapp/resources/$TAUOLADIR/$TAUOLATAR
	+echo Downloading HepMC source from: $HEPMCURL
	+curl -O $HEPMCURL
	+echo Downloading Pythia8 source from: $PYTHIAURL
	+curl -O $PYTHIAURL
	+echo Downloading Photos source from: $PHOTOSURL
	+curl -O $PHOTOSURL
	+echo Downloading Tauola source from: $TAUOLAURL
	+curl -O $TAUOLAURL
	+echo Downloading Sherpa source from: $SHERPAURL
	+curl -O $SHERPAURL

	cd $BUILD_BASE/sources

	@@ -145,6 +175,7 @@
	tar -xzf $BUILD_BASE/tarfiles/$PYTHIATAR
	tar -xzf $BUILD_BASE/tarfiles/$PHOTOSTAR
	tar -xzf $BUILD_BASE/tarfiles/$TAUOLATAR
	+tar -xzf $BUILD_BASE/tarfiles/$SHERPATAR

	# Patch TAUOLA and PHOTOS on Darwin (Mac)
	if [ "$osArch" == "Darwin" ]
	@@ -168,19 +199,19 @@
	mkdir -p $BUILD_BASE/builds/HepMC2
	cd $BUILD_BASE/builds/HepMC2
	$CMAKE -DCMAKE_INSTALL_PREFIX:PATH=$INSTALL_PREFIX $BUILD_BASE/sources/$HEPMC2PKG -Dmomentum:STRING=GEV -Dlength:STRING=MM
	- make
	+ make $BUILDARGS
	make install

	echo Installing pythia8 from $BUILD_BASE/sources/$PYTHIAPKG
	cd $BUILD_BASE/sources/$PYTHIAPKG
	./configure --enable-shared --prefix=$INSTALL_PREFIX
	- make
	+ make $BUILDARGS
	make install

	echo Installing PHOTOS from $BUILD_BASE/sources/$PHOTOSPKG
	cd $BUILD_BASE/sources/$PHOTOSPKG
	./configure --with-hepmc3= --with-hepmc=$INSTALL_PREFIX --prefix=$INSTALL_PREFIX
	- make
	+ make $BUILDARGS
	make install

	if [ "$osArch" != "Darwin" ]
	@@ -188,29 +219,28 @@
	echo Installing TAUOLA from $BUILD_BASE/sources/$TAUOLAPKG
	cd $BUILD_BASE/sources/$TAUOLAPKG
	./configure --without-hepmc3 --with-hepmc=$INSTALL_PREFIX --prefix=$INSTALL_PREFIX
	- make
	+ make $BUILDARGS
	make install
	fi
	-
	else

	echo Installing HepMC3 from $BUILD_BASE/sources/$HEPMC3PKG
	mkdir -p $BUILD_BASE/builds/HepMC3
	cd $BUILD_BASE/builds/HepMC3
	$CMAKE -DHEPMC3_ENABLE_ROOTIO:BOOL=OFF -DHEPMC3_ENABLE_PYTHON:BOOL=OFF -DCMAKE_INSTALL_PREFIX:PATH=$INSTALL_PREFIX $BUILD_BASE/sources/$HEPMC3PKG
	- make
	+ make $BUILDARGS
	make install

	echo Installing pythia8 from $BUILD_BASE/souces/$PYTHIAPKG
	cd $BUILD_BASE/sources/$PYTHIAPKG
	./configure --enable-shared --prefix=$INSTALL_PREFIX
	- make
	+ make $BUILDARGS
	make install

	echo Installing PHOTOS from $BUILD_BASE/sources/$PHOTOSPKG
	cd $BUILD_BASE/sources/$PHOTOSPKG
	./configure --without-hepmc --with-hepmc3=$INSTALL_PREFIX --prefix=$INSTALL_PREFIX
	- make
	+ make $BUILDARGS
	make install

	if [ "$osArch" != "Darwin" ]
	@@ -218,11 +248,18 @@
	echo Installing TAUOLA from $BUILD_BASE/sources/$TAUOLAPKG
	cd $BUILD_BASE/sources/$TAUOLAPKG
	./configure --without-hepmc --with-hepmc3=$INSTALL_PREFIX --prefix=$INSTALL_PREFIX
	- make
	+ make $BUILDARGS
	make install
	fi
	fi

	+echo Installing Sherpa from $BUILD_BASE/sources/$SHERPAPKG
	+cd $BUILD_BASE/sources/$SHERPAPKG
	+autoreconf -i
	+./configure --with-sqlite3=install --prefix=$INSTALL_PREFIX
	+make $BUILDARGS
	+make install
	+
	echo Installing EvtGen from $BUILD_BASE/sources/evtgen
	mkdir -p $BUILD_BASE/builds/evtgen
	cd $BUILD_BASE/builds/evtgen
	@@ -234,13 +271,15 @@
	-DEVTGEN_HEPMC3:BOOL=OFF -DHEPMC2_ROOT_DIR:PATH=$INSTALL_PREFIX \
	-DEVTGEN_PYTHIA:BOOL=ON -DPYTHIA8_ROOT_DIR:PATH=$INSTALL_PREFIX \
	-DEVTGEN_PHOTOS:BOOL=ON -DPHOTOSPP_ROOT_DIR:PATH=$INSTALL_PREFIX \
	- -DEVTGEN_TAUOLA:BOOL=OFF
	+ -DEVTGEN_TAUOLA:BOOL=OFF \
	+ -DEVTGEN_SHERPA:BOOL=ON -DSHERPA_ROOT_DIR:PATH=$INSTALL_PREFIX
	else
	$CMAKE -DCMAKE_INSTALL_PREFIX:PATH=$INSTALL_PREFIX $BUILD_BASE/sources/evtgen \
	-DEVTGEN_HEPMC3:BOOL=ON -DHEPMC3_ROOT_DIR:PATH=$INSTALL_PREFIX \
	-DEVTGEN_PYTHIA:BOOL=ON -DPYTHIA8_ROOT_DIR:PATH=$INSTALL_PREFIX \
	-DEVTGEN_PHOTOS:BOOL=ON -DPHOTOSPP_ROOT_DIR:PATH=$INSTALL_PREFIX \
	- -DEVTGEN_TAUOLA:BOOL=OFF
	+ -DEVTGEN_TAUOLA:BOOL=OFF \
	+ -DEVTGEN_SHERPA:BOOL=ON -DSHERPA_ROOT_DIR:PATH=$INSTALL_PREFIX
	fi
	else
	if [ "$HEPMCMAJORVERSION" -lt "3" ]
	@@ -249,16 +288,18 @@
	-DEVTGEN_HEPMC3:BOOL=OFF -DHEPMC2_ROOT_DIR:PATH=$INSTALL_PREFIX \
	-DEVTGEN_PYTHIA:BOOL=ON -DPYTHIA8_ROOT_DIR:PATH=$INSTALL_PREFIX \
	-DEVTGEN_PHOTOS:BOOL=ON -DPHOTOSPP_ROOT_DIR:PATH=$INSTALL_PREFIX \
	- -DEVTGEN_TAUOLA:BOOL=ON -DTAUOLAPP_ROOT_DIR:PATH=$INSTALL_PREFIX
	+ -DEVTGEN_TAUOLA:BOOL=ON -DTAUOLAPP_ROOT_DIR:PATH=$INSTALL_PREFIX \
	+ -DEVTGEN_SHERPA:BOOL=ON -DSHERPA_ROOT_DIR:PATH=$INSTALL_PREFIX
	else
	$CMAKE -DCMAKE_INSTALL_PREFIX:PATH=$INSTALL_PREFIX $BUILD_BASE/sources/evtgen \
	-DEVTGEN_HEPMC3:BOOL=ON -DHEPMC3_ROOT_DIR:PATH=$INSTALL_PREFIX \
	-DEVTGEN_PYTHIA:BOOL=ON -DPYTHIA8_ROOT_DIR:PATH=$INSTALL_PREFIX \
	-DEVTGEN_PHOTOS:BOOL=ON -DPHOTOSPP_ROOT_DIR:PATH=$INSTALL_PREFIX \
	- -DEVTGEN_TAUOLA:BOOL=ON -DTAUOLAPP_ROOT_DIR:PATH=$INSTALL_PREFIX
	+ -DEVTGEN_TAUOLA:BOOL=ON -DTAUOLAPP_ROOT_DIR:PATH=$INSTALL_PREFIX \
	+ -DEVTGEN_SHERPA:BOOL=ON -DSHERPA_ROOT_DIR:PATH=$INSTALL_PREFIX
	fi
	fi
	-make
	+make $BUILDARGS
	make install

	echo Setup done.
	diff --git a/src/CMakeLists.txt b/src/CMakeLists.txt
	--- a/src/CMakeLists.txt
	+++ b/src/CMakeLists.txt
	@@ -83,7 +83,7 @@


	# Add the EvtGenExternal library (if required)...
	-if( EVTGEN_PYTHIA OR EVTGEN_PHOTOS OR EVTGEN_TAUOLA )
	+if( EVTGEN_PYTHIA OR EVTGEN_PHOTOS OR EVTGEN_TAUOLA OR EVTGEN_SHERPA)
	# Again, first build all the object files (with PIC enabled) so they can be
	# used to build both the shared and static libs
	add_library(objlib_ext OBJECT ${EVTGEN_EXTERNAL_SOURCES})
	@@ -130,6 +130,17 @@
	target_include_directories(objlib_ext PRIVATE ${Tauola++_INCLUDE_DIRS})
	endif()
	endif()
	+ if(EVTGEN_SHERPA)
	+ target_compile_definitions(objlib_ext PRIVATE EVTGEN_SHERPA)
	+ if( ${SHERPA_VERSION} VERSION_GREATER 2.2.15 )
	+ target_compile_definitions(objlib_ext PRIVATE EVTGEN_SHERPA_USEMACRO)
	+ endif()
	+ if (EVTGEN_SUPPRESS_EXTERNAL_WARNINGS)
	+ target_include_directories(objlib_ext SYSTEM PRIVATE ${SHERPA_INCLUDE_DIRS})
	+ else()
	+ target_include_directories(objlib_ext PRIVATE ${SHERPA_INCLUDE_DIRS})
	+ endif()
	+ endif()

	# Now make the shared library from the object files
	add_library(EvtGenExternal SHARED $<TARGET_OBJECTS:objlib_ext>)
	@@ -142,6 +153,14 @@
	target_include_directories(EvtGenExternal PUBLIC ${PYTHIA8_INCLUDE_DIRS})
	target_link_libraries(EvtGenExternal PUBLIC ${PYTHIA8_LIBRARIES})
	endif()
	+ if(EVTGEN_SHERPA)
	+ target_compile_definitions(EvtGenExternal PUBLIC EVTGEN_SHERPA)
	+ if( ${SHERPA_VERSION} VERSION_GREATER 2.2.15 )
	+ target_compile_definitions(EvtGenExternal PRIVATE EVTGEN_SHERPA_USEMACRO)
	+ endif()
	+ target_include_directories(EvtGenExternal PUBLIC ${SHERPA_INCLUDE_DIRS})
	+ target_link_libraries(EvtGenExternal PUBLIC ${SHERPA_LIBRARIES})
	+ endif()
	if(EVTGEN_HEPMC3)
	target_compile_definitions(EvtGenExternal PUBLIC EVTGEN_HEPMC3)
	target_include_directories(EvtGenExternal PUBLIC ${HEPMC3_INCLUDE_DIR})
	@@ -199,6 +218,14 @@
	target_include_directories(EvtGenExternalStatic PUBLIC ${PYTHIA8_INCLUDE_DIRS})
	target_link_libraries(EvtGenExternalStatic PUBLIC ${PYTHIA8_LIBRARIES})
	endif()
	+ if(EVTGEN_SHERPA)
	+ target_compile_definitions(EvtGenExternalStatic PUBLIC EVTGEN_SHERPA)
	+ if( ${SHERPA_VERSION} VERSION_GREATER 2.2.15 )
	+ target_compile_definitions(EvtGenExternalStatic PRIVATE EVTGEN_SHERPA_USEMACRO)
	+ endif()
	+ target_include_directories(EvtGenExternalStatic PUBLIC ${SHERPA_INCLUDE_DIRS})
	+ target_link_libraries(EvtGenExternalStatic PUBLIC ${SHERPA_LIBRARIES})
	+ endif()
	if(EVTGEN_HEPMC3)
	target_compile_definitions(EvtGenExternalStatic PUBLIC EVTGEN_HEPMC3)
	target_include_directories(EvtGenExternalStatic PUBLIC ${HEPMC3_INCLUDE_DIR})
	@@ -255,7 +282,7 @@
	ARCHIVE DESTINATION ${CMAKE_INSTALL_LIBDIR}
	)

	-if( EVTGEN_PYTHIA OR EVTGEN_PHOTOS OR EVTGEN_TAUOLA )
	+if( EVTGEN_PYTHIA OR EVTGEN_PHOTOS OR EVTGEN_TAUOLA OR EVTGEN_SHERPA)
	install(
	TARGETS EvtGenExternal EvtGenExternalStatic
	EXPORT "EvtGenTargets"
	diff --git a/src/EvtGenExternal/EvtExternalGenList.cpp b/src/EvtGenExternal/EvtExternalGenList.cpp
	--- a/src/EvtGenExternal/EvtExternalGenList.cpp
	+++ b/src/EvtGenExternal/EvtExternalGenList.cpp
	@@ -25,6 +25,7 @@
	#include "EvtGenExternal/EvtExternalGenFactory.hh"
	#include "EvtGenExternal/EvtPHOTOS.hh"
	#include "EvtGenExternal/EvtPythia.hh"
	+#include "EvtGenExternal/EvtSherpaPhotons.hh"
	#include "EvtGenExternal/EvtTauola.hh"

	EvtExternalGenList::EvtExternalGenList( bool convertPythiaCodes,
	@@ -80,6 +81,30 @@
	}
	#endif

	+#ifdef EVTGEN_SHERPA
	+EvtAbsRadCorr* EvtExternalGenList::getSherpaPhotonsModel(
	+ const double infraredCutOff, const int mode, const int useME )
	+{
	+ // Define the Photos model, which uses the EvtSherpaPhotonsEngine class.
	+ EvtSherpaPhotons* sherpaPhotonsModel =
	+ new EvtSherpaPhotons( m_useEvtGenRandom, infraredCutOff, mode, useME );
	+ return sherpaPhotonsModel;
	+}
	+#else
	+EvtAbsRadCorr* EvtExternalGenList::getSherpaPhotonsModel(
	+ const double /infraredCutOff/, const int /mode/, const int /useME/ )
	+{
	+ EvtGenReport( EVTGEN_ERROR, "EvtGen" )
	+ << " Sherpa's PHOTONS++ generator has been called for FSR simulation, but Sherpa was not switched on during compilation."
	+ << std::endl;
	+
	+ EvtGenReport( EVTGEN_ERROR, "EvtGen" )
	+ << " The simulation will be generated without FSR." << std::endl;
	+
	+ return new EvtNoRadCorr{};
	+}
	+#endif
	+
	std::list<EvtDecayBase*> EvtExternalGenList::getListOfModels()
	{
	// Create the Pythia and Tauola models, which use their own engine classes.
	diff --git a/src/EvtGenExternal/EvtSherpaPhotons.cpp b/src/EvtGenExternal/EvtSherpaPhotons.cpp
	new file mode 100644
	--- /dev/null
	+++ b/src/EvtGenExternal/EvtSherpaPhotons.cpp
	@@ -0,0 +1,299 @@
	+
	+/***********************************************************************
	+* Copyright 1998-2020 CERN for the benefit of the EvtGen authors *
	+* *
	+* This file is part of EvtGen. *
	+* *
	+* EvtGen 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. *
	+* *
	+* EvtGen 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 EvtGen. If not, see <https://www.gnu.org/licenses/>. *
	+***********************************************************************/
	+
	+#ifdef EVTGEN_SHERPA
	+
	+#include "EvtGenExternal/EvtSherpaPhotons.hh"
	+
	+#include "EvtGenBase/EvtPhotonParticle.hh"
	+#include "EvtGenBase/EvtRandom.hh"
	+#include "EvtGenBase/EvtReport.hh"
	+#include "EvtGenBase/EvtVector4R.hh"
	+
	+#include "ATOOLS/Org/MyStrStream.H"
	+#include "ATOOLS/Phys/Particle.H"
	+#include "SHERPA/Initialization/Initialization_Handler.H"
	+#include "SHERPA/Single_Events/Event_Handler.H"
	+#include "SHERPA/SoftPhysics/Soft_Photon_Handler.H"
	+
	+#include <cstring>
	+#include <iostream>
	+#include <vector>
	+
	+using std::endl;
	+
	+EvtSherpaPhotons::EvtSherpaPhotons( const bool useEvtGenRandom,
	+ const double infraredCutOff, const int mode,
	+ const int useME ) :
	+ m_useEvtGenRandom{ useEvtGenRandom },
	+ m_infraredCutOff{ infraredCutOff },
	+ m_mode{ mode },
	+ m_useME{ useME }
	+{
	+}
	+
	+void EvtSherpaPhotons::initialise()
	+{
	+ if ( m_initialised ) {
	+ return;
	+ }
	+
	+ EvtGenReport( EVTGEN_INFO, "EvtGen" )
	+ << "Setting up Sherpa PHOTONS++ generator for FSR." << endl;
	+
	+ /* Specify whether we are going to use EvtGen's random number generator
	+ * (via EvtSherpaRandom interface) for Sherpa's PHOTONS++ simulation. */
	+ if ( m_useEvtGenRandom ) {
	+ m_configs.push_back( "SHERPA_LDADD=EvtGenExternal" );
	+ m_configs.push_back( "EXTERNAL_RNG=EvtSherpaRandom" );
	+ }
	+
	+ /*
	+ * Internal PHOTONS++ settings.
	+ * Documentation at
	+ * https://sherpa.hepforge.org/doc/Sherpa.html#QED-Corrections
	+ */
	+
	+ /*
	+ * YFS_IR_CUTOFF sets the infrared cut-off which serves as a
	+ * minimum photon energy in this frame for explicit photon generation.
	+ * The default is YFS_IR_CUTOFF = 1E-3 (GeV) but we set it to 1E-7 to equalize
	+ * with the cutoff used for PHOTOS.
	+ */
	+ m_configs.push_back( "YFS_IR_CUTOFF=" + ATOOLS::ToString( m_infraredCutOff ) );
	+
	+ /*
	+ * The keyword YFS_MODE = [0,1,2] determines the mode of operation.
	+ * YFS_MODE = 0 switches Photons off.
	+ * YFS_MODE = 1 sets the mode to "soft only", meaning soft emissions will be
	+ * treated correctly to all orders but no hard emission corrections will be included.
	+ * YFS_MODE = 2 these hard emission corrections will also be included up to
	+ * first order in alpha_QED. This is the default setting in Sherpa.
	+ */
	+
	+ m_configs.push_back( "YFS_MODE=" + ATOOLS::ToString( m_mode ) );
	+
	+ /*
	+ * The switch YFS_USE_ME = [0,1] tells Photons how to correct hard emissions to
	+ * first order in alpha_QED. If YFS_USE_ME = 0, then Photons will use collinearly
	+ * approximated real emission matrix elements. Virtual emission matrix elements of
	+ * order alpha_QED are ignored. If, however, YFS_USE_ME=1, then exact real and/or
	+ * virtual emission matrix elements are used wherever possible.
	+ * These are presently available for V->FF, V->SS, S->FF, S->SS, S->Slnu,
	+ * S->Vlnu type decays, Z->FF decays and leptonic tau and W decays. For all other
	+ * decay types general collinearly approximated matrix elements are used.
	+ * In both approaches all hadrons are treated as point-like objects.
	+ * The default setting is YFS_USE_ME = 1. This switch is only effective if YFS_MODE = 2.
	+ */
	+ m_configs.push_back( "YFS_USE_ME=" + ATOOLS::ToString( m_useME ) );
	+
	+ // TODO: Virtual photon splitting into l+l- will be part of ME corrections from Sherpa 3.0.0 on,
	+ // Once released, this should be switched off by default or
	+ // taken into account while retrieving the event.
	+
	+ // Set up run-time arguments for Sherpa.
	+ std::vector<char*> argv = this->addParameters();
	+
	+ // Create instance and initialise Sherpa.
	+ m_sherpaGen = std::make_unique<SHERPA::Sherpa>();
	+ m_sherpaGen->InitializeTheRun( argv.size(), &argv[0] );
	+ m_sherpaGen->InitializeTheEventHandler();
	+
	+ m_gammaId = EvtPDL::getId( m_photonType );
	+ m_gammaPDG = EvtPDL::getStdHep( m_gammaId );
	+
	+ this->updateParticleLists();
	+
	+ m_initialised = true;
	+}
	+
	+std::vector<char*> EvtSherpaPhotons::addParameters()
	+{
	+ std::vector<char*> argv;
	+ argv.reserve( m_configs.size() );
	+
	+ for ( auto& config : m_configs ) {
	+ if ( config != "Sherpa" ) {
	+ EvtGenReport( EVTGEN_INFO, "EvtGen" )
	+ << " EvtSherpaPhotons::initialise: Setting parameter '"
	+ << config << "'" << endl;
	+ }
	+ argv.push_back( config.data() );
	+ }
	+
	+ return argv;
	+}
	+
	+void EvtSherpaPhotons::updateParticleLists()
	+{
	+ /* Use the EvtGen decay and pdl tables (decay/user.dec and evt.pdl)
	+ * to update Sherpa's KF_Table which contains all defined particles
	+ * and their properties.
	+ * Loop over all entries in the EvtPDL particle data table.
	+ */
	+ const int nPDL = EvtPDL::entries();
	+
	+ for ( int iPDL = 0; iPDL < nPDL; iPDL++ ) {
	+ const EvtId particleId = EvtPDL::getEntry( iPDL );
	+
	+ // Sherpa and EvtGen should use the same PDG codes for particles
	+ const int PDGCode = EvtPDL::getStdHep( particleId );
	+ const long unsigned int particleCode = std::abs( PDGCode );
	+
	+ // If particle is found in Sherpa's KF_Table, then continue.
	+ // Updating the pole mass is not necessary because we provide the 4-momenta
	+ // and the final mass for final-state radiation generation.
	+ ATOOLS::KFCode_ParticleInfo_Map::const_iterator kf_it(
	+ ATOOLS::s_kftable.find( particleCode ) );
	+ if ( kf_it != ATOOLS::s_kftable.end() ) {
	+ continue;
	+ }
	+
	+ // If the PDG is negative, use the charge conjugated ID because
	+ // the KF_Table is defined only for positive PDG numbers.
	+ const EvtId particleIdConj = EvtPDL::chargeConj( particleId );
	+
	+ // Get mass, width, charge and spin
	+ const double mass = EvtPDL::getMeanMass( particleId );
	+ const double width = EvtPDL::getWidth( particleId );
	+ const int charge = PDGCode < 0 ? EvtPDL::chg3( particleIdConj )
	+ : EvtPDL::chg3( particleId );
	+ const int spin = EvtSpinType::getSpin2(
	+ EvtPDL::getSpinType( particleId ) );
	+
	+ // Use as reference the name of the particle (not anti-particle).
	+ const std::string idName = PDGCode < 0 ? particleIdConj.getName()
	+ : particleId.getName();
	+
	+ // Create new entry in the KF_Table. The 0 and 1 in the constructor below
	+ // stand for m_on = 0 and m_stable = 1. These properties are irrelevant
	+ // for final-state radiation and set to default values.
	+ ATOOLS::s_kftable[particleCode] = new ATOOLS::Particle_Info(
	+ particleCode, mass, width, charge, spin, 0, 1, idName, idName );
	+ }
	+}
	+
	+void EvtSherpaPhotons::doRadCorr( EvtParticle* theParticle )
	+{
	+ if ( !theParticle ) {
	+ return;
	+ }
	+
	+ /* Skip running FSR if the particle has no daughters, since we can't add FSR.
	+ * Also skip FSR if the particle has too many daughters (>= 10) as done for PHOTOS.
	+ */
	+ const int nDaughters( theParticle->getNDaug() );
	+ if ( nDaughters == 0 \|\| nDaughters >= 10 ) {
	+ return;
	+ }
	+
	+ ATOOLS::Blob_List* blobs = m_sherpaGen->GetEventHandler()->GetBlobs();
	+
	+ // Use the hadron decay flag always.
	+ // Internally, Sherpa handles tau decays in the same way as hadron decays.
	+ ATOOLS::Blob* blob = blobs->AddBlob( ATOOLS::btp::Hadron_Decay );
	+
	+ // Tell Sherpa that the blob needs FSR (that is extra QED)
	+ blob->SetStatus( ATOOLS::blob_status::needs_extraQED );
	+
	+ // Create mother particle and add it to blob
	+ ATOOLS::Flavour mother_flav( EvtPDL::getStdHep( theParticle->getId() ) );
	+ mother_flav.SetStable( false );
	+ const double motherM0 = theParticle->mass();
	+ const ATOOLS::Vec4D mother_mom( motherM0, 0., 0., 0. );
	+
	+ // Add mother to blob with m_number=-1. The m_number will start from 0 for daughters.
	+ ATOOLS::Particle* mother_part = new ATOOLS::Particle( -1, mother_flav,
	+ mother_mom );
	+ mother_part->SetFinalMass( motherM0 );
	+ mother_part->SetStatus( ATOOLS::part_status::decayed );
	+ // Set m_info="I" (initial) for mother. The m_info will be "F" (final) for daughters.
	+ mother_part->SetInfo( 'I' );
	+
	+ blob->AddToInParticles( mother_part );
	+
	+ // Add daughters to the blob
	+ for ( int iDaug = 0; iDaug < nDaughters; iDaug++ ) {
	+ const EvtParticle* theDaughter = theParticle->getDaug( iDaug );
	+ ATOOLS::Flavour daughter_flav( EvtPDL::getStdHep( theDaughter->getId() ) );
	+ daughter_flav.SetStable( true );
	+
	+ const double daugE = theDaughter->getP4().get( 0 );
	+ const double daugPx = theDaughter->getP4().get( 1 );
	+ const double daugPy = theDaughter->getP4().get( 2 );
	+ const double daugPz = theDaughter->getP4().get( 3 );
	+ const double daugM0 = theDaughter->mass();
	+
	+ const ATOOLS::Vec4D daughter_mom( daugE, daugPx, daugPy, daugPz );
	+
	+ ATOOLS::Particle* daughter_part =
	+ new ATOOLS::Particle( iDaug, daughter_flav, daughter_mom );
	+ daughter_part->SetFinalMass( daugM0 );
	+
	+ daughter_part->SetStatus( ATOOLS::part_status::active );
	+ daughter_part->SetInfo( 'F' );
	+
	+ blob->AddToOutParticles( daughter_part );
	+ }
	+
	+ const SHERPA::Initialization_Handler* inithandler =
	+ m_sherpaGen->GetInitHandler();
	+ SHERPA::Soft_Photon_Handler* softphotonhandler =
	+ inithandler->GetSoftPhotonHandler();
	+
	+ // Simulate the radiation
	+ softphotonhandler->AddRadiation( blob );
	+
	+ // Get number of final-state particles
	+ const int nFinal( blob->NOutP() );
	+
	+ // Retrieve the event from Sherpa blob if FSR photons were added
	+ if ( nFinal > nDaughters ) {
	+ for ( int iLoop = 0; iLoop < nFinal; iLoop++ ) {
	+ const ATOOLS::Particle* outParticle = blob->OutParticle( iLoop );
	+ const ATOOLS::Vec4D daughter_mom = outParticle->Momentum();
	+ const long int pdgId = outParticle->Flav();
	+ const EvtVector4R newP4( daughter_mom[0], daughter_mom[1],
	+ daughter_mom[2], daughter_mom[3] );
	+ const char daugInfo = outParticle->Info();
	+
	+ if ( iLoop < nDaughters ) {
	+ // Update momenta of initial particles
	+ EvtParticle* daugParticle = theParticle->getDaug( iLoop );
	+ if ( daugParticle ) {
	+ daugParticle->setP4WithFSR( newP4 );
	+ }
	+ } else if ( pdgId == m_gammaPDG && daugInfo == 'S' ) {
	+ // Add FSR photons. PHOTONS flags them with info 'S'.
	+ // Create a new photon particle and add it to the list of daughters
	+ EvtPhotonParticle* gamma = new EvtPhotonParticle();
	+ gamma->init( m_gammaId, newP4 );
	+ gamma->setFSRP4toZero();
	+ gamma->setAttribute( "FSR", 1 );
	+ gamma->setAttribute( "ISR", 0 );
	+ gamma->addDaug( theParticle );
	+ }
	+ }
	+ }
	+
	+ return;
	+}
	+
	+#endif
	diff --git a/EvtGenExternal/EvtExternalGenList.hh b/src/EvtGenExternal/EvtSherpaRandom.cpp
	copy from EvtGenExternal/EvtExternalGenList.hh
	copy to src/EvtGenExternal/EvtSherpaRandom.cpp
	--- a/EvtGenExternal/EvtExternalGenList.hh
	+++ b/src/EvtGenExternal/EvtSherpaRandom.cpp
	@@ -18,36 +18,8 @@
	* along with EvtGen. If not, see <https://www.gnu.org/licenses/>. *
	***********************************************************************/

	-#ifndef EVTEXTERNALGENLIST_HH
	-#define EVTEXTERNALGENLIST_HH
	+#ifdef EVTGEN_SHERPA

	-#include "EvtGenBase/EvtAbsRadCorr.hh"
	-#include "EvtGenBase/EvtDecayBase.hh"
	-
	-#include <list>
	-
	-// Description: A factory type method to create engines for external physics
	-// generators like Pythia.
	-
	-class EvtExternalGenList {
	- public:
	- EvtExternalGenList( bool convertPythiaCodes = false,
	- std::string pythiaXmlDir = "",
	- std::string photonType = "gamma",
	- bool useEvtGenRandom = true );
	-
	- virtual ~EvtExternalGenList();
	-
	- std::list<EvtDecayBase*> getListOfModels();
	-
	- EvtAbsRadCorr* getPhotosModel( const double infraredCutOff = 1.0e-7,
	- const double maxWtInterference = 64.0 );
	-
	- protected:
	- private:
	- std::string m_photonType;
	-
	- bool m_useEvtGenRandom;
	-};
	+#include "EvtGenExternal/EvtSherpaRandom.hh"

	#endif
	diff --git a/test/CMakeLists.txt b/test/CMakeLists.txt
	--- a/test/CMakeLists.txt
	+++ b/test/CMakeLists.txt
	@@ -34,7 +34,7 @@
	if (EVTGEN_HEPMC3)
	target_compile_definitions(${test_exe} PRIVATE EVTGEN_HEPMC3)
	endif()
	- if( EVTGEN_PYTHIA OR EVTGEN_PHOTOS OR EVTGEN_TAUOLA )
	+ if( EVTGEN_PYTHIA OR EVTGEN_PHOTOS OR EVTGEN_TAUOLA OR EVTGEN_SHERPA )
	target_compile_definitions(${test_exe} PRIVATE EVTGEN_EXTERNAL)
	target_link_libraries(${test_exe} PRIVATE EvtGenExternal)
	endif()
	diff --git a/test/testDecayModel.cc b/test/testDecayModel.cc
	--- a/test/testDecayModel.cc
	+++ b/test/testDecayModel.cc
	@@ -113,9 +113,7 @@
	m_config.at( "models" ).get<std::vector<std::string>>() };
	const auto modelParameters{
	m_config.at( "parameters" ).get<std::vector<std::vector<std::string>>>() };
	- const auto outFileName{ m_config.at( "outfile" ).get<std::string>() };
	const auto nEvents{ m_config.at( "events" ).get<int>() };
	- const auto refFileName{ m_config.at( "reference" ).get<std::string>() };

	// Then check for optional fields, setting default values if not present

	@@ -131,6 +129,31 @@
	? m_config.at( "extras" ).get<std::vector<std::string>>()
	: std::vector<std::string>{} };

	+ // Set the FSR generator. Use PHOTOS by default.
	+ const auto fsrGenerator{
	+ ( m_config.contains( "fsr_generator" ) )
	+ ? m_config.at( "fsr_generator" ).get<std::string>()
	+ : "PHOTOS" };
	+
	+ // Set reference and output file names, insert fsrGenerator name if FSR simulation is not deactivated
	+ const bool noFSR = std::find( extraCommands.begin(), extraCommands.end(),
	+ "noFSR" ) != extraCommands.end();
	+
	+ const std::string fileNameEnd = noFSR ? ".root"
	+ : "_" + fsrGenerator + ".root";
	+
	+ const auto outFileStrSize =
	+ m_config.at( "outfile" ).get<std::string>().size() - 5;
	+ const auto refFileStrSize =
	+ m_config.at( "reference" ).get<std::string>().size() - 5;
	+
	+ const auto outFileName =
	+ m_config.at( "outfile" ).get<std::string>().substr( 0, outFileStrSize ) +
	+ fileNameEnd;
	+ const auto refFileName =
	+ m_config.at( "reference" ).get<std::string>().substr( 0, refFileStrSize ) +
	+ fileNameEnd;
	+
	const auto debugFlag{ ( m_config.contains( "debug_flag" ) &&
	m_config.at( "debug_flag" ).is_boolean() )
	? m_config.at( "debug_flag" ).get<bool>()
	@@ -159,7 +182,19 @@
	bool convertPythiaCodes( false );
	bool useEvtGenRandom( true );
	EvtExternalGenList genList( convertPythiaCodes, "", "gamma", useEvtGenRandom );
	- radCorrEngine = genList.getPhotosModel();
	+ if ( fsrGenerator == "PHOTOS" ) {
	+ radCorrEngine = genList.getPhotosModel();
	+ } else if ( fsrGenerator == "SherpaPhotons1" ) {
	+ radCorrEngine = genList.getSherpaPhotonsModel( 1e-7, 1, 0 );
	+ } else if ( fsrGenerator == "SherpaPhotons20" ) {
	+ radCorrEngine = genList.getSherpaPhotonsModel( 1e-7, 2, 0 );
	+ } else if ( fsrGenerator == "SherpaPhotons21" ) {
	+ radCorrEngine = genList.getSherpaPhotonsModel( 1e-7, 2, 1 );
	+ } else {
	+ std::cerr << "ERROR: The option fsr_generator = '" << fsrGenerator
	+ << "' is not supported. " << std::endl;
	+ return false;
	+ }
	extraModels = genList.getListOfModels();
	#endif

	@@ -811,12 +846,19 @@
	value = p1.get( 3 );

	} else if ( !selectedVarName.compare( "cosHel" ) \|\|
	- !selectedVarName.compare( "absCosHel" ) ) {
	+ !selectedVarName.compare( "absCosHel" ) \|\|
	+ !selectedVarName.compare( "cosHelParent" ) ) {
	// Cosine of helicity angle
	EvtVector4R p12;
	EvtVector4R p1Res;

	- if ( d2 != 0 ) {
	+ if ( !selectedVarName.compare( "cosHelParent" ) ) {
	+ p12 = selectedParent->getP4Lab();
	+ const EvtVector4R boost{ p12.get( 0 ), -p12.get( 1 ), -p12.get( 2 ),
	+ -p12.get( 3 ) };
	+ // Momentum of particle d1 in resonance frame, p1Res
	+ p1Res = boostTo( p1_lab, boost );
	+ } else if ( d2 != 0 ) {
	// Resonance center-of-mass system (d1 and d2)
	p12 = p1_lab + p2_lab;
	// Boost vector
	@@ -1387,8 +1429,10 @@

	int main( int argc, char* argv[] )
	{
	- if ( argc != 2 ) {
	- std::cerr << "Expecting one argument: json input file" << std::endl;
	+ if ( argc != 2 && argc != 3 ) {
	+ std::cerr << "Expecting at least one argument: json input file."
	+ << "\nOne additional argument supported for fsrGenerator"
	+ << std::endl;
	return 1;
	}

	@@ -1398,6 +1442,10 @@
	inputStr >> config;
	inputStr.close();

	+ if ( argc == 3 ) {
	+ config["fsr_generator"] = argv[2];
	+ }
	+
	bool allOK{ true };
	if ( config.is_array() ) {
	for ( const auto& cc : config ) {
	diff --git a/validation/CMakeLists.txt b/validation/CMakeLists.txt
	--- a/validation/CMakeLists.txt
	+++ b/validation/CMakeLists.txt
	@@ -33,7 +33,7 @@
	if (EVTGEN_HEPMC3)
	target_compile_definitions(${validation_exe} PRIVATE EVTGEN_HEPMC3)
	endif()
	- if( EVTGEN_PYTHIA OR EVTGEN_PHOTOS OR EVTGEN_TAUOLA )
	+ if( EVTGEN_PYTHIA OR EVTGEN_PHOTOS OR EVTGEN_TAUOLA OR EVTGEN_SHERPA)
	target_compile_definitions(${validation_exe} PRIVATE EVTGEN_EXTERNAL)
	target_link_libraries(${validation_exe} PRIVATE EvtGenExternal)
	endif()

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