Implementation of Chamber Misalignments and Deformations in the HCP 2007 Implementation of Chamber Misalignments and Deformations in the ATLAS Muon Spectrometer Description N.Benekos1, L.Chevalier2, S.Goldfarb3, R. Harrington4, J.F.Laporte2, I.Logashenko4, J.Miller4, R. Nicolaidou2, A.Ouraou2,D.Rebuzzi5, M.Schott1, S.Spagnolo6, N. van Eldik7, M.Verducci8, S.Willocq7 1 Max Planck Institut, 2 DAPNIA-Saclay, 3 Univ. of Michigan, 4 Boston Univ., 5 Pavia Univ. and INFN, 6 Salento Univ. and INFN, 7 Univ. of Massachusetts, 8 CERN

Requirements: Tracking (triggering) for pT>6 GeV/c up to = 2.7(2.4) pT resolution from 3% to 10% at pT=1TeV/c Precision provided at run-time by the optical alignment system in terms of 6 shift and tilt angles +8 deformation parameters 3 measurement stations sagitta for muons of 1TeV/c is 500 mm chamber position must be known to  30mm in the barrel, 40 mm in the endcaps  The detector description sw must handle alignment and deformation parameters as condition data The current MS geometry description, initialised with the primary numbers in the geometry DB and based on GeoModel (a set of geometrical primitives for the construction of a transient model the ATLAS detector) and translated with a parser into a GEANT4 representation for simulation offers a first successful implementation of misalignments applied as run-time corrections to the nominal layout and deformation parameters 1/pT pull distribution cot pull distribution The strategy for implementing deformations: most MDT deformation effects can be described with rigid tubes tilted and shifted w.r.t. their nominal location in the chamber Detector Description can apply one extra individual transform to each tube in order to provide a realistic chamber geometry to all reconstruction applications Pulls of reconstructed track parameters in a misaligned layout (red) and after correcting for misalignments by accessing a condition database (blu)