For a long time, high energy physics experiments have been striving to develop software tools for the complete description of detector models based a single source of information. For the success of an experiment it is important to provide a consistent detector description to simulation, reconstruction and analysis applications from a single source. When referring to the detector description this includes, in addition to the geometry and the materials used in the device, also parameters describing e.g. the detection techniques, constants required for alignment and calibration, description of the readout structures and conditions data.
The main motivation behind the DD4hep package is to devise a toolkit that addresses all these issues for all the stages of an experiment. It was designed based on experiences from the LHCb experiment, as well as from developments in the Linear Collider community. The tool relies on usage of pre-existing and widely used software, combining it into a consistent generic detector description. The main components are the ROOT geometry package, which is used for construction and visualization of geometry, and the Geant4 simulation toolkit, which can be interfaced via DD4hep to perform detector simulation in complex detector designs.
The intent is to provide a comprehensive detector description for the quantification of the detector and provide all the information necessary for interpretation of data form the experiment. From past experiences it can be established that a comprehensive view, not limited only to geometry, is extremely advantageous for the construction of a complete set of tools aimed at data interpretation, e.g. alignment, where detector positions vary over time and need to be matched with the geometry for reconstruction.
The conception of the toolkit was driven mainly by the following requirements:
- Complete Detector Description: provides full detector geometry, the materials used when building the structures, visualization attributes, detector readout information, alignment, calibration and environmental parameters.
- Coverage of the full life cycle of the experiment: supports all stages from detector concept development, detector optimization, construction, operation and at the same time enables easy transition from one stage to the next.
- Single source of information: provides a consistent detector description, for simulation, reconstruction, analysis.
- Ease of Use: delivers a simple and intuitive interface, with minimal external dependencies.
The core element of DD4hep is the the so-called Generic Detector Description Model (GDDM). The figure below depicts the interaction of the main components of DD4hep and their interfaces to the end-user applications, namely the simulation, reconstruction, alignment and visualization. The generic detector description is an in-memory model, that consists of a set of objects containing geometry and auxiliary information about the detector.
It is envisioned that the GDDM can be constructed through several means, but current development is focused on a mechanism that converts a compact detector description in XML format through specialized code fragments (called Detector constructors) into the GDDM. These code fragments instantiate the GDDM of the detector defined by a set of C++ classes. From this model it is possible to transform in memory the GDDM to e.g. Geant4 geometry or a GDML file.
Development of DD4hep
DD4hep is been developed and maintained by:
- Markus Frank, CERN
- Andre Sailer, CERN
- Frank Gaede, DESY
- Marko Petric, CERN
The following authors, in alphabetical order, have contributed to DD4hep:
- Christian Grefe, CERN
- Christoph Rosemann, DESY
- Daniel Jeans, KEK
- Georgios Voutsinas, DESY
- Joschka Lingemann, CERN
- Nikiforos Nikiforou, CERN
- Pere Mato Vila, CERN
- Shaojun Lu, DESY