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GENIE neutrino generation

aegir-genie generates neutrino interactions with GENIE inside an aegir job. It is a phlex source plugin, genie_source, that publishes MCParticle vectors like aegir's other generators.

FairShip runs GENIE as a chain of command-line steps (gmkspl → gevgen → gntpc → vertex re-placement). The plugin drives a genie::GMCJDriver directly instead. It convolves the SHiP neutrino flux with the cross-section splines and the GeoModel geometry, so interaction vertices follow the same material that Geant4 tracks through, and it keeps count of protons on target.

Repository: ShipSoft/aegir-genie

API reference: Doxygen

Why a separate repository

GENIE is GPL-licensed, so anything that links it becomes a combined GPL work. aegir is LGPL-3.0-or-later and must not depend on GENIE, which is why everything that links GENIE lives in aegir-genie. The SHiP-authored sources there are LGPL-3.0-or-later as well; only the plugin binary, linked against GENIE, is distributed under GPL-3.0-or-later. aegir never links this code. Phlex finds the plugin at run time through PHLEX_PLUGIN_PATH.

aegir itself contains genie_reader_source, which reads GENIE rootracker files with plain ROOT I/O. That path needs no GENIE libraries and serves as the validation reference for the embedded source.

Installing

aegir-genie and the production cross-section splines are packaged on the prefix.dev/ship-experiment/stable channel:

pixi workspace channel add https://prefix.dev/ship-experiment/stable
pixi add aegir aegir-genie genie-splines-ship

genie-splines-ship installs the splines as $CONDA_PREFIX/share/genie-splines-ship/gxspl-ship.xml. The example workflows are installed under $CONDA_PREFIX/share/aegir-genie/workflows/.

To build from source:

git clone https://github.com/ShipSoft/aegir-genie.git
cd aegir-genie
pixi run build
pixi run test

Running

Two example workflows are included:

  • workflows/genie_st.jsonnet: a short single-threaded chain with a schema-v1 SHiP flux file.
  • workflows/genie_ship_full.jsonnet: the full chain on the production geometry with the neutrino group's GSimple flux, as used for validation.

Both need a flux file, the spline XML and a GeoModel geometry database. The geometry, Geant4 and output plugins in these workflows come from aegir, so run full chains from an environment that has aegir and its Geant4 data, with aegir-genie's plugin on PHLEX_PLUGIN_PATH and GENIE pointing at share/genie. The aegir-genie README covers the configuration keys, both flux formats and the gevgen_ship validation tool.