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Detector Description in LHCb

This workshop focuses on the architecture of the LHCb detector description, including topics such as visualization, interfacing with Geant4, and the condition database. It also discusses the use of XML files for persistent representation and the implementation of the conditions database.

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Detector Description in LHCb

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  1. Detector Description in LHCb Detector Description Workshop 13 June 2002 S. Ponce, P. Mato / CERN

  2. Contents • Architecture • Transient layer • Persistency layer : XML • Condition Database • Visualization • Interfacing Geant4 • Status & examples LHCb Detector Description

  3. Architecture Overview Visualization (Panoramix) XML Transient Store Simulation (Gauss/Geant4) Calibration Condition Database Materials Structure Reconstruction (Brunel) Geometry … Analysis (Da Vinci) GDML ? DAQ ? LHCb Detector Description

  4. Converter Converter Application Manager Converter Event Selector Transient Event Store Data Files Message Service Persistency Service Event Data Service JobOptions Service Algorithm Algorithm Algorithm Data Files Transient Detector Store Particle Prop. Service Persistency Service Detec. Data Service Other Services Data Files Transient Histogram Store Persistency Service Histogram Service Architecture • Sub-Architecture of Gaudi • Same principles • Transient/Persistent representations • Focus on the “Physics Algorithm” • Coherent access to “all” detector data • Geometry, Calibration, Slow Control, etc. Gaudi Architecture LHCb Detector Description

  5. Logical Structure • The basic object is a Detector Element • Identification • Navigation (tree-like) • DetElement as information center • Be able to answer any detector related question • E.g. global position of strip#, temperature of detector, absolute channel gain, etc. • Placeholder for specific code • The specific answers will be coded by “Physicists” DetElement * MyDetector LHCb Detector Description

  6. ReadOut DetElement MuonStation Algorithm Accessing Detector Data • Manages store • Synchronization updates beginEvent DetectorData Service Persistency Service request request: get, update Transient Detector Store Geometry Conversion Service IDetElement IGeometryInfo GeometryInfo Algorithm ICalibration Conditions DB Calibration Conversion Service IReadOut reference Other DBs Conversion Service LHCb Detector Description

  7. Material Solid DataObject PVolume LVolume Element Mixture Solid Solid ReadOut SolidBox Isotope MuonStation DetectorElement Calibration Simplified Diagram Association resolved on demand Hierarchy * IDetectorElement IGeometryInfo GeometryInfo ILVolume IReadOut * IMaterial ISolid IPVolume ICalibration * * Specific detector description questions from algorithms Detector Description Geometry Material LHCb Detector Description

  8. Persistency based on XML files • XML is used as persistent representation of the Structure, Geometry and Materials (eventually also Conditions) • Mapping each C++ class into an XML element • Inheritance emulation (Generic and Specific Detector Element) • Relationships using “Links” and symbolic names • Allow math expressions with parameters and physical units • Using expression evaluator (available in CLHEP) LHCb Detector Description

  9. XML Files • Separated XML files • By sub-detector and data type (structure, geometry, material) • Low coupling of developments • Links between files through references • allows to see the whole description as a single XML tree • Versioning done using CVS • Possible migration to the “Conditions DB” LHCb Detector Description

  10. XML Converters • Capable of converting (one way for the time being) XML into C++ objects • Using DOM interface (Xerces-C) • Specific converters for specific “DetElement” (to be provided by users) • Available Converters • Structure: Catalog, DetElement • Geometry: LVolume, Surface, Solids (various shapes, boolean), PVolumes (parametric) • Materials: Isotope, Element, Mixture, TabulatedProperty LHCb Detector Description

  11. XML Detector Description Editor • Developed a graphical editor to “hide” XML to the end-users (physicists) • It understands our model (DTD) • But it’s generic (possible to use another DTD) • It understands “links” and allow us to edit a web of XML files as a single tree • It’s implemented in Java (portable) LHCb Detector Description

  12. XMLEditor LHCb Detector Description

  13. Conditions DB • Accessing detector conditions data (calibration, slow control, alignment, etc.) should be the same as geometry data • Time validity period and Versioning in addition • Conditions are integrated into the transient data model • Converters are responsible for converting from database rather than from XML • Conditions are attached to Detector Elements as for geometry • each element has many conditions (calibration, alignment, slowcontrol, fastcontrol …) LHCb Detector Description

  14. Conditions DB Implementation • Condition objects are stored in XML • The XML fragments are stored using the Oracle condition DB developed by IT • XML references are used to select between XML and condition DB : • <conditionref href=“../Ecal/condition.xml#caEcal"/>  XML • <conditionref href=“cond://dd/Calibration/Ecal/caEcal"/>  DataBase LHCb Detector Description

  15. Geometry Visualization • Visualization is essential for developing the geometry • Applicable at the different data representations • Generic geometry information conversion to 3D graphics data • Panoramix (OnX) Structure+ Geometry Vis Display CnvSvc Transient Store Visual CnvSvc Display Giga CnvSvc G4 Geometry Visual CnvSvc Display LHCb Detector Description

  16. Interfacing With Geant4 • We integrate Gaudi with Geant4 by providing a number of “Gaudi Services” (GiGa) • The GiGaGeomCnvSvc is able to convert transient objects (DetElem, LVolume, Surfaces, etc.) into G4 geometry objects • The conversion does not require “user” code • Flexibility in mapping Gaudi model to Geant4 model • Single source of Geometry information LHCb Detector Description

  17. Status of LHCb Detector Description • The DetDesc framework is fully functional (transient classes, XML DTD, XML converters, editor, etc) • All sub-detectors are already described (structure, geometry and materials) using the provided framework • Visualization based on OnX : Panoramix. Allows to see geometry, events, histograms, … • Conversion to Geant4 through GiGa is complete LHCb Detector Description

  18. Example 1 : Velo and Rich1 LHCb Detector Description

  19. Example (2) : Zoom on Ecal LHCb Detector Description

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