LEGEND integration

[sethrj]

This is the primary tracking issue for integrating Celeritas with the simulation workflow for the LEGEND experiment. The primary Celeritas contact points are the "assignees" to the right.

Core capabilities

• Optical photon physics: Add optical photon simulation #886
• ORANGE for platform portability: Convert Geant4 geometry to ORANGE #1167

Notes

• Framework: https://github.com/legend-exp/remage
• Optical physics simulation: https://doi.org/10.1140/epjc/s10052-023-11354-9

[drbenmorgan]

I'm happy to be added as a preliminary contact point if you want here as I'm officially in LEGEND.

[sethrj]

From Matthew Green:

To start, we simulate scintillation photons produced in liquid argon, in which we approximate the blue curve in the figure as a gaussian distribution centered at 128nm with sigma = 2.929nm, emitted isotropically.

We voxelize the detector in 5mmx5mmx5mm voxels, generate scintillation photons, track. In addition to the scintillation, we also include wavelength shifting in TPB and wavelength-shifting optical fibers and scintillation in PEN plastic.

Everthing inside the double-walled steel cyrostat is argon, but it is partitioned by that vertical copper can into 2 regions. In the outer region, where things are essentially axially symmetric, we use the axial symmetry to effectively generate a 2D probability map in R, Z. In the inner region, where the axial symmetry is broken, we generate the map fully in 3D. In both cases we generate random points within the voxel boundary, sample whether that point is in LAr, and if so, throw a photon. If not, resample.

Maps look something like this:

Inner region (left-most) is a 2d slice from a 3d map, middle/outer regions are the 2D map in R,z.