This page last edited on December 11, 2015


The requirements for the detector data model has been captured in the document "GAUDI Detector Data Model" by R. Chytracek (pdf, fm).

Detector Geometry Model

The detector geometry is described in some detail in the Gaudi Users Guide in the Detector Description chapter. Please refer to it to get an overview. The following documents are the reference documents for the different parts of the software.

XML Description (DDDB)

The Detector structure, Geometry and Materials are described in XML files with the following DTD (see also DTD source files). To edit the detector description you can use a normal text editor to edit XML files or alternatively use the graphical XML editor developed to understand our Detector Description model. Please refer to the available XML editor documentation for details on how to access and use it.

All the XML files for the current LHCb detector description are stored in an sqlite database (CondDB). Instructions on how to use this database are available here. Prior to the migration to the sqlite database, the Xml files were kept in CVS, in the package Det/XmlDDDB.

You can check for overlapping volumes, correct material distributions etc. using one of the methods described in the Gauss FAQ. The list of current known overlaps can be found here

The LHCb Geometry (see also simplified geometry)

Each detector element class must have a unique Class ID. Look at the list of existing Class IDs. If you are coding a new detector element, choose a new ClassID in the appropriate range, and notify the detector description coordinator, who will update the list.

Sub-SystemDocumentation, Description, Notes,...
Beam PipeDescription of the Beam Pipe Geometry
MagnetDescription of the Magnet Geometry, B-field maps
VeloSee Velo software TWiKi. Also LHCb-2007-061
Rich SystemSee Rich software TWiKi
Silicon TrackerSee ST DetDesc pages.
Outer Tracker See Main OT home page and OT software TWiki. See also: LHCb 2003-062, LHCb-2004-114, Presentation at the tracking workshop, Amsterdam, 2003-11-19
CaloDescription of ECAL and HCAL geometry, CaloDet Twiki
MuonSee Muon software TWiKi
Radiation maps DC06 (XmlDDDB v30r3), Simplified geometry (SQLDDDB v2r2), RTTC

Geometry Framework and Alignment

The LHCb detector description framework has been extended to allow for detector misalignments, that is, detector positions which deviate from the ideal, or nominal, position. The generic geometry and alignment framework is described in the Geometry Framework TWiki. The specific LHCb alignment activities and procedures are documented in the LHCb Detector Alignment TWiki.


Large sections of the Simulation Advanced Tutorial on 21-22 February 2012 were devoted to detector description.

Older (not completely up to date) documentation includes a previous version of the tutorial, a recipe and a note on extending the detector element for sub-detector geometry information.

Documents and Presentations


  • Detector Description for the current detector - basic principles, essential & weak points from the reconstruction and simulation viewpoints, by G.Corti, 6th LHCb Computing Workshop, 2015-11-18 (slides)


  • Tools for going from global to local misalignments, by J.Palacios, T-Rec, CERN, 2007-07-09 (pdf)


  • Detector description framework in LHCb, by S. Ponce, CERN.
    CHEP 2003, San Diego, USA, March 24-28, 2003 (paper.pdf, transparencies.ppt)


  • Extended presentation to the RTAG 7 (Detector Geometry & material Description), by S.Ponce, CERN, 4/07/2002 (ppt, pdf, ps)
  • Presentation to the RTAG 7 (Detector Geometry & material Description), by S.Ponce, CERN, 14/06/2002 (ppt, pdf, ps)
  • Handling Several Geometry Configurations in XML, by S. Ponce, 10th LHCb Software Week, CERN, 08/03/2002 (ppt, pdf)


  • The LHCb detector description DTD, by S. Ponce, CERN, 31/08/2001 (pdf, fm)
  • Extending detector elements and implications, by S. Ponce, CERN, 31/08/2001 (pdf, fm)
  • The XML Editor, by S. Ponce, CERN, 07/05/2001, (pdf, fm)


  • XML in LHCb Detector Description Framework, by R. Chytracek  at XML Detector Description for HEP workshop 14/04/2000 (ppt)
  • LHCb detector description framework, by R. Chytracek, CHEP 2000, Padova (Italy) , slides (ppt), paper (pdf)