Outline

1. Detector Descriptionof theATLAS Muon Spectrometerand H8 Muon TestbeamD. PomarèdeCEA/DAPNIA/SEDI/LILAS - Saclay

2. Outline • The ATLAS Muon Spectrometer • Challenges of the Muon Detector Description • Integration in the ATLAS software chain • Implementation in the ATLAS Simulations and Data Challenges • Implementation in the H8 Muon Testbeams • Conclusions & Plans

3. The ATLAS Muon Spectrometer • High-momentum final-state muons are among the most promising and robust signatures of physics at the Large Hadron Collider (LHC) • To exploit this potential, the ATLAS Collaboration has designed a high-resolution muon spectrometer with stand-alone triggering and momentum measurement capability • The final aim is to reach the highest efficiency with stand-alone mo-mentum resolution of a few % at 10-100 GeV/c and ~10% at 1 TeV/c • The spectrometer is based on the magnetic deflection of tracks in large superconducting air-core toroid magnets. The tracks are measured in chambers laid out in three layers. An optical alignment system controls the relative positioning of chambers at the 30 mm level. • The layout of the detectors and their intrinsic design are optimized to provide the best acceptance and resolution, taking into account the high-level background environment, the inhomogeneous magnetic field, and the large size of the apparatus.

4. The ATLAS Muon Spectrometer Muon Chambers EndCap Toroid Magnet Barrel Toroid Magnet 24 meter diameter 44 meter length

5. Challenges of the Muon Detector Description • Four technologies of detectors are used : • Precision chambers : MDT (Monitored Drift Tubes Chamber) and CSC (Cathode Strips Chamber) • Trigger chambers : RPC (Resistive Plate Chamber) and TGC (Thin Gap Chamber) • A large number of chambers with different properties : • E.g. ~1200 MDT chambers • Rectangular or trapezoidal shapes with various sizes • 1 or 2 Multilayer per chamber • 3 or 4 layers of tubes per Multilayer • 30 to 72 tubes per layer • Some chambers have cutouts Example : EndCap Outer Large MDT chamber dim 1.4 x 6.2 meters 2 Multilayers with 3 layers 48 tubes / layer

6. Challenges of the Muon Detector Description • A complex layout • Organization in Large and Small sectors associated with the eight Magnet coils • Cylindrical symmetry broken by the feet : special sectors • Mirror symmetry z+/z- broken by holes for access and services (cables, cryo- genics) Layout of the Barrel MDT chambers with the Barrel Toroid and Feets

7. Complex layout of chambers in the bending plane Challenges of the Muon Detector Description Trigger and 2nd coordinate Measurements B Z-axis (LHC beam) Interaction point Precision Measurements in 3 locations in the bending plane

8. Challenges of the Muon Detector Description • Alignment of chambers • 6 parameters per chamber to describe the translations and rotations w.r.t nominal positions • Deformations of chambers : 8 parameters (Torsion, Cross Plate Sag (RO/HV), Cross Plates elongations (RO/HV), Long- beam sags, Trapezoid effect) + global Temperature expansion Barrel Outer Large MDT chamber with a combination of Torsion (100 mm) and Cross Plate sags (50 mm) EndCap Middle Large MDT chamber with a 150 mm Torsion

9. Challenges of the Muon Detector Description • A precise description of the passive materials is needed to account for the multiple Coulomb scattering and energy losses : Magnets, Supports, Shields Barrel and EndCap Toroids, Shields and Support Structures

10. Implementation and integration in the ATLAS SW Chain • The detector description relies on two key components : the Database that holds the geometrical parameters and the software that access it and builds the geometry • The entire chain of simulation, reconstruction, calibration packages depend upon the Detector Description • A stable and robust implementation is required • It must be flexible enough to answer the need of schema evolution and allow for possible layout changes : one version of the software should handle many different possible geometrical configurations held in the Detector Description Database • Database distribution (GRID-based operation) • The AMDB ascii file is the primary source for geometry parameters • “Atlas Muon DataBase” specific to the Muon system • Structured organization of active elements (detectors) • reproduce the natural symmetries of the detector • compact, object-oriented • indexing of objects similar to the offline identifier scheme • XML description of passive elements (AGDD) • Visualization tool to develop and debug the geometry : Persint • The Oracle Detector Description Database is a unified source of the AMDB parameters for the detector description packages • Common to all ATLAS subsystems (Calorimeters, Inner Detectors) • Supported by CERN-IT, MySQL-replicas available • Versioning supported to allow for multiple versions of the geometry, Browser

11. AMDB DESCRIPTION OF ACTIVE ELEMENTS • Example of Barrel Inner Large (BIL) chambers layout

12. AMDB/XML DESCRIPTION OF DEAD MATTER • Example of Disk Shield Small Wheel Hub : Primary variables volume polycone with two child-elements (polyplanes) Composition of volumes : Disk Shield

13. Oracle DDDB Browser Tags of ALMN tables (definition of objects in Muon stations) AMDB tables

14. Tag Hierarchy Browser List of tags of AMDB List of tags of ATLAS geometry List of tags of Muon geometry Tags of AMDB tables

15. Implementation and integration in the ATLAS SW Chain • The software packages retrieve the parameters from the DB and provide the geometrical informations to the clients in the software framework : • the Amdcsimrec package provides a set of methods to obtain all geome-trical informations to build the internal geometry of the client applications • tightly coupled to the AMDB database • schema evolution : a number of different geometries can be described with a single implementation of the software • complex volumes are described using boolean volume operations • visualization tool : Persint • the MuonGeoModel package introduced in 2003 • uses a geometry kernel common with all other ATLAS subsystems : • the GeoModel kernel provides a set of geometrical primitives of common use (tube, box, polyhedron, …) • detector-specific services that are not described in a generic way are implemented as an additional layer • it provides volume operations • it has CLHEP as sole dependency • visualization tool : HEPVis • used by Geant4 simulations

16. Implementation and integration in the ATLAS SW Chain • Implementation with the MuonGeoModel package : A picture of the whole system Barrel & CSC Stations EndCap Stations & Innert Materials

17. Implementation and integration in the ATLAS SW Chain MDT & RPC internal structure EC tubes staircasing BMS MDT+RPC stations CSC internal structure

18. Implementations in the Simulations and Data Challemges • The design of the Spectrometer was optimized using this Detector Description : • ATLAS Muon Spectrometer Technical Design Report, 1997 • Evaluation of the ATLAS Physics performance (“Layout M”) • Geant3 simulations • Detector and Physics Performance Technical Design Report, 1999 • Studies of realistic service and access holes, 2001 • ATLAS Data Challenge 1 (“Layout P”), 2001-2002 • Geant3 simulations • Athens Physics Workshop 2003 • ATLAS Data Challenge 2 (“Layout Q”), Ongoing • Geant4 simulations • GRID based • Rome Physics Workshop, June 6-11 2005

19. Simulations • Example of Higgs to four muons event. Detector Description AMDB, Track reconstruction Muonboy, Display Persint

20. H8 MUON TESTBEAM • Major testbeams have been conducted at the CERN-SPS H8 line since 2001 to test the Muon detectors • One of the main objective was to validate the concept of the optical alignment systems of the Muon chambers. • Detector Description is a key component of these tests : • Description of the nominal geometry • Misalignment of chambers w.r.t nominal positions • Deformations of chambers • Implementation of the geometrical models in both the alignment reconstruction programs (analysis/fitting of data from optical devices) and track reconstruction • Also, test of the description of dead materials : comparison MC/data • Analyses have demonstrated that the geometry can be controlled using alignment corrections from the optical alignment systems • various movements (translations, rotations) and deformations tested • Barrel and EndCap systems • chambers aligned at the 30 micron level

21. Combined Testbeam Geometry H8-2004 Combined Testbeam final configuration : 15 MDTs, 7 RPCs, 3 TGCs, 1 CSC Iron Dump Barrel setup (2 towers MDT+RPC) EndCap MDT setup CSC BIS chamber Rotating BIL BOS MDT+RPC station TGCs Magnets

22. H8 MUON TESTBEAM TYPICAL ENDCAP EVENT

23. H8 MUON TESTBEAM TYPICAL ENDCAP EVENT

24. Conclusions and plans • A well established Detector Description used in the optimization of the detector and throughout the evaluations of the Physics perfor-mance of ATLAS : large-scale simulations and testbeams • Plans : • Commissioning of Muon Spectrometer with cosmics • Barrel Sector 13 : 6 BML and 6 BOL stations, summer 2005 • Data Challenge 3 / Computing System Commissioning • with the most up-to-date geometry (“Layout R”) • misaligned / deformed chambers • Refinements of the chambers description • chamber intrinsic properties from X-ray tomography or analyses of cosmic-ray test stands : tube pitches, non-parallelism of multilayers • Refinements of dead matter description • electronics, cables, patch panels • additional dead matter : access platforms

25. Description of Access Platforms • Example of current developments : description of the access platforms clamped on the Barrel Toroid struts = additional contribution to Multiple Coulomb scatterring

26. Description of Access Platforms