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Requirements.md

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Geant4 Exacale Proxy Requirements

Description of the functionality necessary for the Geant Exascale Proxy

The proxy should be a standalone application with a mean to explore various detector layouts, for example the CMS detector and a Liquid Argon TPC. It should provide interfaces for configuration and options for transport, event input, and output and either indirectly or directly include performance measurement tools.

The primary goal of the proxy is to explore the best ways to leverage the type of coprocessor (GPGPU) expected in the next generation of HPC machines (even if this require more code and dependency than a typical proxy application)

Configuration interfaces

  1. physics lists
  2. detector descriptions (eg. GDML)
  3. input event types

Transport Options

For a reasonably representative example (described in particle-proposal.md) of simulation, we find that processing photon, e-, e+, p+, p-, take have about 80% of the cpu time specifically dedicated to particle processing and represents 70% of the number of particles. If we also include neutrons, pi+, pi-, and protons this goes up to 99% of the cpu time and 98% of the number of particles. In addition the code for the simulating the former set exist in a easier-to-extract form than for the later set.

Given these ratio, in the first phase the application should focus on:

  • charged particles in uniform electromagnetic field
  • realistic electromagnetic field description used in typical HEP experiments
  • standard set of electromagnetic physics processes and models required for most of HEP detector simulation, including:
    • Charged particles
      • Ionization
        • Bremsstrahlung
        • Multiple scattering models (electron and positron)
    • Photons
      • Photoelectric Effect
      • Compton Scattering
      • Pair-production

and later extent to:

  • Hadronic physics models for:
    • Proton
    • Neutron
    • Pion
    • Kaons
  • Parameterized particle shower simulations

Event Input

  • Particle gun win customizations:
    • number of particles
    • particle types
    • random distributions in energy, eta, phi in given ranges
    • Ability to use HEPevents (for an example, BSM events from PYTHIA) would be a plus

Output

The proxy should be capable of producing output data representative of a typical HEP experiment, for example digitized hits (scoring) in sensitive detectors.

Performance Measurements

The proxy should include (directly or indirectly) the ability to measure:

  1. scalability
  2. event throughput
  3. memory usage under various configuration settings, including multi-threaded execution

Additional Notes

An estimate of the date size for input events for a real physics process (for example Higgs -> ZZ , Z to all decays, O(1000) primary tracks) is in the order of 10's of kilobytes (for example 32K/event at the LHC energy). A typical output rate is in the order of 1.5 MB per event (for simulated data, compared to about 1MB for the equivalent real data.)