Simulation steps

The simulation is a chain or series of steps each modeling a specific physical process. The following picture describes the general workflow and the products. Each piece will be described in detail.


Beam Simulation

  • Generates neutrino flux hitting the detector
  • Simulated sources can include accelerator, sun, astrophysical sources, KDAR sources, etc. (so not strictly from accelerator beams)

The beam simulation is external to LArSoft

The beam simulation combines geometry with hadronic physics, energy loss and decays to produce a simulated, predicted flux. Initial particles are 120 GeV or 8 GeV protons for NuMI or BNB, respectively, or 60 to 120 GeV protons for LBNF. Primary tools are Geant4 and PPFX. In principle, fluka together with flugg can be used as well.

Event Generation

Event generation

  • Produces final state secondaries from neutrino interactions within the detector based on input flux description
  • For proton decays and radiologicals, just generates decay signatures
  • Output is list of final state particles in simb::MCTruth

Can run different generators using the same flux files as input.

Specific detector simulation

The stage of converting energy depositions into “raw digits” involves the specific technology of the detector. Only the LAr experiments can make much use of code sharing due to the significant differences.

Some experiments that involve light collection use Geant to do that part of simulation, either directly embedded in the framework, or as a separate simulation that provides distributions that can be sampled (mostly for speed and efficiency.)

Electron Response

Detector response for electrons

  • Field effects, noise, electronics transfer function, etc.
  • Output is fully simulated TPC readout channel

Photon Detector Response


Detector response for photons:

  • Photon transport, photo-detector quantum efficiency, noise, electronics transfer function, etc.
  • Output is fully simulated photo-detector readout channel

For more information, please see Erica Snider’s Introduction to LArSoft – source material.

For information about simulations in general, please consult Robert Hatcher’s Simulation Tools in Neutrino Experiments.