SoLID Detector Simulation (DD4hep)

DD4hep detector description and Geant4 simulation setup for SoLID (Solenoidal Large Intensity Device, JLab Hall A). It covers full SoLID and the staged SoLID-Lite configurations, follows the EIC software conventions (DD4hep + ddsim/npsim + EDM4hep), and runs in the eic-shell container.

• Wiki
• Design and conventions: docs/design.md
• Comparison with solid_gemc and the reference documents: docs/geometry_comparison.md
• Line-view drawings (DAWN replacement): docs/visualization.md
• Reconstruction framework and container environment: docs/reconstruction.md

Detector overview

Full SoLID in its SIDIS (polarized ³He) and PVDIS (LD₂, baffles) setups, and SoLID-Lite J/ψ, drawn from the DD4hep geometry with make_solid_views --views overview. The other configurations are linked in the table below.

Configurations

compact file	experiment	magnet / field	GEMC reference	overview
solid.xml = solid_SIDIS_He3.xml	SIDIS, polarized 3He (40 cm, z = -350 cm)	CLEO-II, longer endcap (v4c) / CLEOv9	solid_SIDIS_He3_moved_full	drawing
solid_SIDIS_NH3.xml	SIDIS, polarized NH3 (+ 5 T target field)	v4c / CLEOv9	solid_SIDIS_NH3_moved_full	drawing
solid_PVDIS.xml	PVDIS, 40 cm LD2 (z = +10 cm), baffles	v4c / CLEOv9	solid_PVDIS_LD2_moved_full	drawing
solid_JPsi.xml	J/psi, 15 cm LH2 (z = -315 cm)	v4c / CLEOv9	solid_JPsi_LH2_moved_full	drawing
solid_DDVCS.xml	J/psi + DDVCS forward muon detector	v4c / CLEOv9	solid_JPsi_DDVCS_LH2_moved_full	drawing
solid_JPsi_lite.xml	SoLID-Lite J/psi (stage 1)	CLEO-II iron as built / CLEOv10	solid_JPsi_LH2_lite_full	drawing
solid_DDVCS_lite.xml	SoLID-Lite DDVCS	CLEO-II iron as built / CLEOv10	solid_JPsi_DDVCS_LH2_lite_full	drawing
solid_beamtest.xml	beam-test placeholder (telescope Cherenkov)	none	–	–

Subsystems: CLEO-II solenoid (yoke, coil, cryostat), targets and beamlines, PVDIS baffles, GEM trackers, light-gas and heavy-gas Cherenkovs (plus the SoLID-Lite CO2 Cherenkov), shashlik ECal (forward and large angle, with preshower), scintillator pad detectors, forward MRPC, and the DDVCS muon system. All coordinates are in the GEMC hall frame: z along the beam, origin at the coil center.

Quick start

Get the container and build the geometry in it (Linux with Apptainer/Singularity; macOS and options: containers/README.md):

containers/install.sh --build
containers/solid-shell -c solid_JPsi_lite        # shell with the SoLID environment

The equivalent steps by hand, inside eic-shell or containers/solid-shell:

cmake -B build -S . -DCMAKE_INSTALL_PREFIX=install
cmake --build build -j4 && cmake --install build
source install/bin/thissolid.sh solid_JPsi_lite        # sets DETECTOR, DETECTOR_PATH, DETECTOR_CONFIG, LD_LIBRARY_PATH

# simulate (field maps are downloaded once into $DETECTOR_PATH/fieldmaps)
ddsim --steeringFile $DETECTOR_PATH/steering/solid_sim.py -N 100 --outputFile out.edm4hep.root

# check geometry and compare with GEMC
python3 scripts/geometry/check_geometry.py $DETECTOR_PATH/$DETECTOR_CONFIG.xml
python3 scripts/geometry/compare_gemc.py $DETECTOR_CONFIG --gemc /path/to/solid_gemc

# line drawings (SVG/PDF/PNG)
make_solid_views -o views
make_solid_views -o views --views overview             # the labelled overviews shown above

steering/solid_sim.py turns on optical photons for the gas Cherenkovs (SOLID_OPTICAL=0 switches them off) and places the default electron gun at the target of the selected configuration.

Repository layout

solid_*.xml        top-level configurations
compact/           definitions (system ids), materials, display, subsystem fragments, configs/ (shared detector sets)
src/               DD4hep plugins: SoLID_CLEOMagnet, SoLID_FieldMapB, SoLID_Beamline, SoLID_PolHe3Target,
                   SoLID_PolNH3Target, SoLID_CryoTarget, SoLID_PVDISBaffle, SoLID_GEMTracker, SoLID_LightGasCherenkov,
                   SoLID_SectorGasCherenkov, SoLID_HexShashlykEMCal, SoLID_ScintPadDisk, SoLID_MRPCDisk,
                   SoLID_MuonDetector (+ beam-test SoLID_TelescopeCherenkov)
steering/          ddsim steering
scripts/geometry/  check_geometry.py, solid_geo_dump.py, compare_gemc.py, gemc_txt.py
bin/               solid_lineview, make_solid_views (installed with thissolid.sh)
test/              stand-alone test configurations per subsystem
containers/        install.sh, solid-shell launcher, solid_xl Dockerfile (eic_xl + solid_dd4hep, optional Gaudi)
docs/              design, comparison, visualization, reconstruction
benchmarks/        LGC optical-photon study; ECal (Juggler era, to be ported to EICrecon)

Status (November 2026)

All configurations load and are free of overlaps at 1 um tolerance. Subsystem placements were validated against the GEMC geometry files, from 10^-9 cm to 0.1 mm depending on the subsystem. Hits were checked in every sensitive detector. Deliberate deviations from GEMC are listed in docs/geometry_comparison.md. The main one: the CLEO-II octagonal yoke uses the real flat-to-flat dimensions, where GEMC builds it about 8 % too large.

Open items:

• the 3D field map of the v4 yoke is missing upstream;
• there is no field map for the SoLID-Lite SIDIS magnet stage;
• the lite forward-angle segment azimuths are still under discussion;
• the beam-test geometry has not been ported;
• the ACTS material map has to be regenerated.