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.

Core capabilities

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

[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 XLZD integration #1401