LZ integration

[sethrj]

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

LZ is running simulation campaigns until 2030, so we have to work fast to make an impact.

Optical photons come from:

• S1: prompt scintillation
• S2: delayed electrons that drift up through the field: signal strength depends on energy and electric field, but generally orders of magnitude greater than S1

The S1 photons are currently handled by NEST external framework, which essentially all TPC experiments use:

• During EM transport, cluster energy depositions based on some input detector resolution
• NEST returns the number of photons generated

If the S2 photons are handled explicitly:

• Energy deposition is clustered and saved
• During digitization ("Detector electronics response"), electrons from deposition are drifted through the electric field, emitting photons on the way
• Position of those photons generate detector responses using optical map

Another mode of execution doesn't handle optical photons explicitly at all, it uses the parameterised LZLAMA model to determine detector responses directly.

Core capabilities

• [x] ORANGE for platform portability: https://github.com/celeritas-project/celeritas/issues/1167

Optical physics

• [ ] Core photon physics: https://github.com/celeritas-project/celeritas/issues/886
• [ ] Physics importing through GDML
• [ ] Diffuse reflective (Lambertian) boundaries

Constructing an optical map:

• [ ] Gaussian source description: https://gitlab.com/seriksen/S2LightMaps
• [ ] Tallying time bin * spatial bin * detector

EM physics

• [ ] Electric field
• [ ] Region/volume specific physics
• [ ] Neutron physics
• [ ] Custom neutron physics
• [ ] Custom xenon scintillation physics

[sethrj]

Notes on today's meeting with @seriksen:

• LZ currently uses optical maps due to prohibited cost of inline optical tracking (Would very much like to do optical photons inline to the veto detectors.)
• Three detectors LZ: inner TPC, skin, outer detector
• Optical maps are done for the inner TPC (top 5-10cm), 1cm voxels for a total 15 billion photons (ish): 10 nodes * 256 threads -> 24 hours wall time
• Record hits and time on PMT surfaces (no direction, no position)
• Run geant4 in 2 modes: energy deposit (no optical photons), then PMT output (using optical map). - BACCARAT requires Geant4 10.3
• Next detector: XLZD #1401

[sethrj]

From the LZ GDML file we have:

Surface Name	Surface Type	Finish
diffuseReflectorOpSurface	dielectric_dielectric	groundfrontpainted
gasXeSteelSurface	dielectric_metal	polished
aluminumQuartzSurface	dielectric_metal	polished
gasXeTeflonSurface	dielectric_dielectric	groundfrontpainted
liquidXeTeflonSurface	dielectric_dielectric	groundfrontpainted
gasXeTitaniumSurface	dielectric_metal	polished
liquidXeTeflonSurfaceBskinPMT	dielectric_dielectric	groundfrontpainted
liquidXeTeflonSurfaceDomePMT	dielectric_dielectric	groundfrontpainted
liquidXeTeflonSurfacePMT	dielectric_dielectric	groundfrontpainted
liquidXeTitaniumSurface	dielectric_metal	polished
gasXeBlackSurface	dielectric_dielectric	groundfrontpainted

And all report a "value" (aka sigma_alpha) of 1.0.