Configuration Reference¶

larnd-sim is controlled by a set of YAML configuration files and optional look-up-table (LUT) binary files. The sections below describe each file type, its location inside the repository, and the key fields it contains.

Pixel Layout ¶

Directory: larndsim/pixel_layouts/

A pixel layout file (YAML) describes the physical arrangement of LArPix channels across all tiles and anodes. It provides:

Channel mapping (chip → pixel ID)
Pixel pitch
Tile positions and orientations
TPC geometry

The files are produced by larpix-geometry.

File	Description
`multi_tile_layout-2.3.16.yaml`	Module 0 (v2a, realistic dead channels)
`multi_tile_layout-2.4.16.yaml`	Generic LArPix v2a, 2×2 module
`multi_tile_layout-2.5.16.yaml`	Generic LArPix v2b, 2×2 module
`multi_tile_layout-3.0.40.yaml`	LArPix v2b/v3, ND-LAr module

Note

The suffix .16 / .40 indicates the number of tiles per anode. For 2.4.16 and 2.5.16 all channels are activated; 2.3.16 includes realistic dead-channel masking from Module 0 data taking.

Detector Properties ¶

Directory: larndsim/detector_properties/

A detector properties YAML file sets physical detector constants that are loaded into larndsim.consts.detector and larndsim.consts.light. Key fields include:

Electric field (e_field)
Electron lifetime
Pixel response sampling / bin sizes
Light-related constants (trigger windows, SiPM response model, etc.)

Per-module variations (for 2x2_mod2mod_variation) are also expressed here.

Simulation Properties ¶

Directory: larndsim/simulation_properties/

Controls algorithmic parameters loaded into larndsim.consts.sim:

Batch sizes (batch_size, event_batch_size, write_batch_size)
Number of sampled points per segment
MC truth tracking settings (MAX_MC_TRUTH_IDS)

Response File ¶

A NumPy .npy binary containing the near-field charge induction look-up table. The table is produced from finite-element-method (FEM) electric-field simulations.

Directory: larndsim/bin/

File	Pixel pitch / ASIC version
`response_44.npy`	4.4 mm pitch (LArPix v2a)
`response_38.npy`	3.8 mm pitch (LArPix v2b / v3)

Warning

The RESPONSE_BIN_SIZE and RESPONSE_SAMPLING constants in the detector properties YAML must match the response file selected.

Light Look-Up Table (LUT)¶

The light LUT encodes the photon visibility from each voxel in the active TPC volume to each SiPM channel. It is produced with a GEANT4 optical simulation using ArgonCubeLUTSim.

A 2×2 example LUT is shipped at larndsim/bin/lightLUT.npz. Higher resolution LUTs (required for production-quality simulations) are hosted on NERSC.

Light Detector Noise ¶

An .npy file containing the per-channel FFT noise spectrum extracted from single-module cosmic-ray runs.

Example: larndsim/bin/light_noise_2x2_4mod_July2023.npy

Optional Inputs ¶

Bad channels ¶

A JSON or YAML file listing LArPix chip keys whose channels should be deactivated in the simulation. If omitted, all channels are treated as active.

Pixel thresholds ¶

Provides a channel-by-channel discriminator threshold. If omitted, every channel uses the global fee.DISCRIMINATION_THRESHOLD value.

Pixel gains ¶

Provides a channel-by-channel front-end gain factor. If omitted, every channel uses the global fee.GAIN value.

Configuration YAML (keyword presets)¶

The named keyword configurations (module0, 2x2, …) are defined in larndsim/config/config.yaml. Each entry maps a keyword to a complete set of the file paths described above. You can add custom entries to this file or override individual fields via the command-line interface.