G4LArBox

G4LArBox transports generated particles through one configurable box of liquid argon. The detector model is intentionally small: an active G4_lAr box inside an invisible vacuum world. The simulation records particle steps, tracks, the liquid-argon medium response, and generator truth in a ROOT file.

Run

The self-contained route is Docker:

docker build --platform linux/amd64 -t g4larbox .
mkdir -p data
docker run --rm --platform linux/amd64 \
  -v "$PWD/data:/opt/G4LArBox/data" \
  g4larbox

The pinned image is linux/amd64. On an ARM machine, prefer a remote amd64 builder: compiling the dependency stack under local emulation is resource intensive.

This runs simplebox.mac with singlegun.mac and writes data/output.root. Choose another generator macro by replacing the image's default arguments:

docker run --rm --platform linux/amd64 \
  -v "$PWD/data:/opt/G4LArBox/data" \
  g4larbox -d simplebox.mac -g marley.mac

For a local build, provide Geant4, ROOT, GSL, CMake, Git, and Make, then run:

cmake -S . -B build
cmake --build build -j2
./G4LArBox -d simplebox.mac -g singlegun.mac

CMake fetches and builds MARLEY and BxDecay0 under the ignored extern/ directory when they are not already present.

The box

simplebox.mac defines a one-metre cube. The three detector commands accept any positive length:

/box/width 1 m
/box/height 1 m
/box/length 1 m

Set G4LARBOX_RANDOM_SEED for a repeatable run and G4LARBOX_OUTPUT_FILE to change the output path.

Generators

All generators feed the same box and write to the same truth tree.

Mode	Example macro	Input
Geant4 GPS	singlegun.mac	/gps/* commands
GENIE GST	genie_gst.mac	gst tree in a ROOT file
GENIE nucleon decay	genie_pdecay.mac	final-state arrays in a gst tree
CORSIKA	corsika_cosmics.mac	converted corsika tree
CORSIKA + GENIE	corsika_overlay_genie.mac	one tree of each type
MARLEY	marley.mac	JSON configuration or event file
BxDecay0	bxdecay0_Ar39.mac, bxdecay0_Co60.mac, bxdecay0_Rn222.mac	configured isotope
Radiological activity	radiological.mac	isotope activities in the macro
Rock neutrons	rock_neutrons.mac	spectrum and rate in the macro

The GENIE and CORSIKA examples expect user-supplied ROOT files at the paths shown in their macros.

GENIE input is read with momenta in GeV and optional vertices in metres and seconds. CORSIKA trees use the branches iev, nprimary, pdg, px, py, pz, x, y, z, and t, with momenta in GeV, positions in metres, and times in seconds. Input exhaustion is an error unless the corresponding cycleEvents command is enabled.

MARLEY can generate from config/marley_ve40ar_mono.js or replay an event file with /generator/marley/file. BxDecay0 also exposes dbd, dbdranged, mdl, and mdlr commands under /generator/bxdecay0/.

Radiological activity may be used as its own source or overlaid on another mode with /generator/radiological/enable true. Rock neutrons can likewise be overlaid with /generator/rockNeutrons/enable true.

Output

The output file contains four trees:

• stepTree: deposited energy, step geometry, particle IDs, and medium response
• trackTree: particle vertices, endpoints, momenta, and ancestry
• eventTree: total excitons, ions, scintillation photons, and electrons
• truthTree: source-specific metadata and all injected primary particles

The original quick-look trajectory and lifetime plots remain available:

cd data
mkdir -p plots
./runplots.sh output.root