Extending Geant4 Parallelism with External Libraries (MPI, TBB) and Its Use on HPC Resources

With Geant4 Version 10.0, released in December 2013, one of the most widely used Monte-Carlo codes has been ported to take full advantage of multi- and many-core CPUs thanks to the introduction of event-level parallelism via multithreading. In this paper we review recent developments to allow for a better integration of parallel Geant4 jobs with external libraries. We have chosen to develop examples using the popular Intel Threading Building Block (for short TBB) as an alternative parallelization approach to the native Geant4 POSIX. To simplify the scaling of a Geant4 application across nodes on a cluster we are improving the support of MPI in Geant4. In particular it is now possible to run an hybrid MPI/MT application that uses MPI to scale across nodes and MT to scale across cores. %The recent developments allow users to easily implement parallel application resources that scale on a very large number of nodes and cores typical of HPC resources.Comment: conferenc

Interfacing Geant4, Garfield+ plus and Degrad for the simulation of gaseous detectors

© 2019 For several years, attempts have been made to interface Geant4 and other software packages with the aim of simulating the complete response of a gaseous particle detector. In such a simulation, Geant4 is always responsible for the primary particle generation and the interactions that occur in the non-gaseous detector material. Garfield++ on the other hand always deals with the drift of ions and electrons, amplification via electron avalanches and finally signal generation. For the ionizing interaction of particles with the gas, different options and physics models exist. The present paper focuses on how to use Geant4, Garfield++ (including its Heed and SRIM interfaces) and Degrad to create the electron–ion pairs stemming from the ionization of the gas. Software-wise, the proposed idea is to use the Geant4 physics parameterization feature, and to implement a Garfield++ or Degrad based detector simulation as an external model. With a Degrad model, detailed simulations of the X-ray interaction in gaseous detectors, including shell absorption by photoelectric effect, subsequent Auger cascade, shake-off and fluorescence emission, become possible. A simple Garfield++ model can be used for photons (Heed), heavy ions (SRIM) and relativistic charged particles or MIPs (Heed). For non-relativistic charged particles, more effort is required, and a combined Geant4/Garfield++ model must be used. This model, the Geant4/Heed PAI model interface, uses the Geant4 PAI model in conjunction with the Heed PAI model. Parameters, such as the lower production cut of the Geant4 PAI model and the lowest electron energy limit of the physics list have to be set correctly. The paper demonstrates how to determine these parameters for certain values of the W parameter and Fano factor of the gas mixture. The simulation results of this Geant4/Heed PAI model interface are then verified against the results obtained with the stand-alone software packages.keywords: Gaseous detectors, Monte-carlo simulation, Particle interactions, Software engineering, Geant4status: publishe

Where Brain, Body and World Collide

The production cross section of electrons from semileptonic decays of beauty hadrons was measured at mid-rapidity (|y| < 0.8) in the transverse momentum range 1 < pt < 8 Gev/c with the ALICE experiment at the CERN LHC in pp collisions at a center of mass energy sqrt{s} = 7 TeV using an integrated luminosity of 2.2 nb^{-1}. Electrons from beauty hadron decays were selected based on the displacement of the decay vertex from the collision vertex. A perturbative QCD calculation agrees with the measurement within uncertainties. The data were extrapolated to the full phase space to determine the total cross section for the production of beauty quark-antiquark pairs