The G4HepEm R&D Project

The G4HepEm R&D project was initiated by the Electromagnetic Physics Working Group of the Geant4 collaboration as part of looking for solutions to reduce the computing performance bottleneck experienced by the High Energy Physics (HEP) detector simulation applications.

Description

The project (initially) targets the most performance critical part of the HEP detector simulation applications, i.e. the EM shower generation covering $e^{-}/e^{+}$ and $\gamma$ particle transport. By

starting from the EM physics modelling part, the project isolates and extracts all the data and functionalities required for EM shower simulation in HEP detectors in a clear, compact and well documented form
investigates the possible computing performance benefits of replacing the current general particle transport simulation stepping-loop of Geant4 by alternatives, highly specialised for particle types and tailored for HEP detector simulation applications
by providing a clear, compact and well documented environment for EM shower generation (already connected to Geant4 applications), the project also provides an excellent domain for further related R&D activities.
especially, the projects facilitates R&D activities targeting EM shower simulation on GPU by providing:
- functionalities of making all required physics data available on the main device memory, together with example kernels for their run-time usage.
- isolated, self-contained (i.e. "single function") implementations of both the physics related parts of the stepping loop and all required physics interactions

All details can be found in the documentation.

Requirements

G4HepEm is one of the ongoing developments, carried out within the EM physics working group of the Geant4 collaboration. It has been made available in order to facilitate and catalyse correlated R&D activities by providing and sharing the related expertise and specific knowledge. Therefore, G4HepEm is tightly connected to and depends on the Geant4 simulation toolkit.

The only requirement of G4HepEm is a recent Geant4 version to be available on the system. The recommended version, Geant4-10.7.p01 is available at the corresponding Geant4 Download area. All information regarding the Prerequisites of Geant4 as well as the detailed Geant4 Installation Instructions can be found in the related sections of the Geant4 Installation Guide.

Quick start

More detailed instructions can be found in the Build and Install section of the documentation.

It is assumed in the followings, that the required version of the Geant4 toolkit is installed on the system and the corresponding Geant4Config.cmake CMake configuration file is located under the G4_INSTALL directory. Then building and installing G4HepEm (under the G4HepEm_INSTALL directory) can be done by simple:

$ git clone https://github.com/mnovak42/g4hepem.git    
$ cd g4hepem/
$ mkdir build
$ cd build/
$ cmake ../ -DGeant4_DIR=G4_INSTALL -DCMAKE_INSTALL_PREFIX=G4HepEm_INSTALL
$ make install

Example: build and execute an example application

After building and installing G4HepEm under the G4HepEm_INSTALL directory, the g4hepem/apps/examples/TestEm3 (general) simplified sampling calorimeter example application can be built and executed as:

$ cd g4hepem/apps/examples/TestEm3/
$ mkdir build
$ cd build/
$ cmake ../ -DGeant4_DIR=G4_INSTALL -DG4HepEm_DIR=G4HepEm_INSTALL/lib/cmake/G4HepEm/  
$ make
$ ./TestEm3 -m ../ATLASbar.mac

Execute the application as ./TestEm3 --help for more information and see the g4hepem/apps/examples/TestEm3/ATLASbar.mac example input macro file for more details.