material_tables.md

Generation of Material Tables

Guide to generate material property tables for XML files for DD4hep.

Procedure

1. Build executables from source in src/ by running make.
2. Execute bin/generate_material_tables. This will produce XML nodes for each material and optical-surface property table, which can be copied into any relevant XML files. Plots of the property tables will also be produced, but note that step 3 will extend or override these plots; always refer to the plots from step 3 in place of those from step 2, since in some cases, the step 2 tables are out of date
3. Extrapolate tables to broader ranges using scripts/extrapolate_material_tables.py; these tables should be used in place of the ones from step 2

Code

• src/g4dRIChOptics.hh: Common class hierarchy for dRICH material optical properties, originally from cisbani/dRICh
• text/drich-materials.txt: Geant4 text-file description of materials, needed along with src/g4dRIChOptics.hh for the generation of property tables
• src/generate_material_tables.cpp: Executable for generating the XML nodes and plots
• scripts/extrapolate_material_tables.py: Extrapolate material property tables beyond g4dRIChOptics
• src/surfaceEnums.h: helper methods for Geant4 surface properties

Material Property Tables Status

Aerogel

Material

• using CLAS12 experimental points rescaled by Alessio/GEMC, in range 200 to 660 nm
  • except for absorption length, where we use data from Aerogel Factory
• needed to do curve fits for extrapolation
• EXTRAPOLATION: refractive index
  • fit to 2nd order Sellmeier function
  • upper limit 660 nm extrapolated to 1000 nm
• EXTRAPOLATION: absorption length
  • linear fit to 870 nm and above only
  • upper limit extrapolated to 1000 nm
• EXTRAPOLATION: Rayleigh scattering length
  • fit to lambda^4 dependence
  • upper limit 660 nm extrapolated to 1000 nm

Surface

• TODO

Airgap

• using common AirOptical
• no effect switching to C2F6 (which disables it)
• no extrapolation

Acrylic Filter

Material

• using (adjustable) cutoff of 300 nm
• no effect switching to C2F6 (which disables it)
• no extrapolation

Surface

• TODO

Gas

Material

• currently 200-700nm, 10 points
• straightforward to adjust in Evaristo's code, g4dRIChOptics.hh
• EXTRAPOLATION: refractive index
  • extrapolated to 200-1000nm, 16 points
  • done for both C2F6 and C4F10
• EXTRAPOLATION: absorption length
  • is constant
  • same range as refractive index
  • done for both C2F6 and C4F10
• TODO: use Rayleigh scattering length?
  • also is constant, but not used in epic

Surface

• TODO?

Mirror

Material

• same as filter material
• TODO: update to a more realistic material

Surface

• model exists from Evaristo's code, but we are not using this since reflectivity seems too low
• instead, using constant 0.9 reflectivity for all wavelengths: 1-7 eV = 177-1240nm
• no extrapolation, since wavelength range is large enough
• TODO: update to a more realistic model or measurement

Sensors

Material

• Material is currently AirOptical, to correctly model the gas/sensor optical boundary
• TODO: do this more correctly

Surface

• table EFFICIENCY is set to constant 1 for all wavelengths 1-7 eV = 177-1240nm
• actual quantum efficiency is applied downstream in reconstruction