SHiP Geometry

This repository contains the SHiP experiment geometry implementation using GeoModel.

The SHiP geometry is described using GeoModel and is used by the simulation and digitisation/reconstruction packages which are developed in a separate repository.

Coordinate System

• Origin: target front face (first tungsten disk)
• Z-axis: along beam direction (positive downstream)
• Y-axis: vertical (against gravity)
• X-axis: horizontal, perpendicular to beam (completes right-handed system)
• Units: mm (GeoModel native), angles in radians
• Beam axis height: 1.7 m above floor

Implementation Status

Subsystem	Status	Description
Cavern	Complete	World volume with subtracted rock cavities
Target	Complete	19 W slabs with Ta cladding in Inconel vessel
MuonShield	Approximate	6 stations, box approximations of arb8 shapes
Magnet	Approximate	Iron yoke with box-shaped coils (should be tubes)
DecayVolume	Approximate	Rectangular vessel (should be frustum)
TimingDetector	Complete	330 scintillator bars via GeoModelXML
UpstreamTagger	Approximate	Monolithic slab (needs bar segmentation)
Trackers	Envelope only	4 empty station boxes
Calorimeter	Envelope only	3 empty component boxes (ECAL front/back, HCAL)

Building

Prerequisites

• CMake 3.16 or later
• C++20 compatible compiler
• GeoModel libraries (GeoModelCore, GeoModelIO, GeoModelTools) version 6.22+

Build Instructions

# Configure
cmake -B build -DCMAKE_BUILD_TYPE=Release

# Build
cmake --build build

# Run tests
ctest --test-dir build

Build Geometry

# Build the complete SHiP geometry
./build/apps/build_geometry [output_file.db]

# View in gmex
gmex output_file.db

Installing

cmake --install build --prefix /path/to/install

This installs the headers, libraries, and SHiPGeometryConfig.cmake so that downstream projects can locate the package:

find_package(SHiPGeometry CONFIG REQUIRED)
target_link_libraries(myapp PRIVATE SHiPGeometry::SHiPGeometry)

The package config calls find_dependency for GeoModelCore, GeoModelIO, and GeoModelTools automatically.

Architecture

Factory Pattern

Each subsystem is implemented as a factory class:

class FooFactory {
public:
    explicit FooFactory(SHiPMaterials& materials);
    GeoPhysVol* build();
private:
    SHiPMaterials& m_materials;
};

SHiPGeometryBuilder::build() orchestrates all factories, creating the world volume (Cavern) and placing each subsystem at its global z-position.

Materials

All materials are managed centrally by SHiPMaterials. To use an existing material in a factory:

const GeoMaterial* iron = m_materials.requireMaterial("Iron");

To add a new material, edit src/SHiPMaterials.cpp:

1. Add elements in createElements() if not already present
2. Add the material in createMaterials() with composition and density
3. Call material->lock() after defining the composition

Adding or Modifying a Subsystem

1. Header: subsystems/<Name>/include/<Name>/<Name>Factory.h — declare the factory class with dimension constants as static constexpr members
2. Implementation: subsystems/<Name>/src/<Name>Factory.cpp — implement build() using GeoModel primitives (GeoBox, GeoTubs, GeoLogVol, GeoPhysVol, GeoTransform, etc.)
3. Registration: add a build() + placement call in src/SHiPGeometry.cpp (SHiPGeometryBuilder::build())
4. CMake: add sources/headers to subsystems/<Name>/CMakeLists.txt
5. Docs: update the subsystem README.md with geometry tree, materials, and status

Structure

geometry/
├── include/SHiPGeometry/   # Public headers (SHiPGeometry, SHiPMaterials)
├── src/                     # Core implementation
├── subsystems/              # Detector subsystem factories
│   ├── Cavern/
│   ├── Target/
│   ├── MuonShield/
│   ├── Magnet/
│   ├── DecayVolume/
│   ├── Trackers/
│   ├── Calorimeter/
│   ├── UpstreamTagger/
│   └── TimingDetector/
├── apps/                    # build_geometry, validate_geometry
├── tests/                   # Unit tests
└── cmake/                   # CMake package config

Reference GDML

The reference GDML exported from FairShip is not tracked in this repository (ignored via .gitignore). To obtain it, export from FairShip and place in gdml/. The gdml2gm tool does not support GDML assemblies, so direct conversion is not possible — the GDML serves as a numerical reference for geometry parameters during C++ implementation.

License

The SHiP geometry is distributed under the GNU Lesser General Public License v3.0 or later (LGPL-3.0-or-later). See the LICENSE file for details.

Copyright is held by CERN for the benefit of the SHiP Collaboration. Some components are distributed under different licenses and copyrights — see the individual file headers and the LICENSES directory for details. This project follows the REUSE specification for licensing information.