The barrel reference system1 THE BARREL REFERENCE SYSTEM C.Guyot (Saclay) Goal: Provide a geometrical survey of the whole barrel muon spectrometer giving the absolute chamber positions with a precision < 0.5 mm on translation and < 0.5 mrad on rotations Why: Correction of the projective system sagitta prediction Pattern recognition requirements (relative chamber positions are needed with a precision < 1mm ) Magnetic field reconstruction (aims at a reconstruction of the toroid coil positions w.r.t. chambers with a precision of about 1mm)

The barrel reference system2 dd Rotation axis Chamber rotated by an angle  Distance d between the plane of the projective sensors plane and the wire plane Projective sensors  Wire plane Correction to the projective system sagitta prediction The projective system predicts zero sagitta correction for this muon whereas a false sagitta of the of order  d is measured with the wire plane. With d = 50mm, the angle  has to be known with a precision < 0.5 mrad to keep this error on the sagitta below 25  m. BIL BML BOL

The barrel reference system3 Principle of the reference system (only one sector shown) (camera - LED sources)

The barrel reference system4 Reference system implementation: plate-chamber connection Closed wheel of plate-plate connections Foot plate BIL BIR BML Standard sector plate

The barrel reference system5 Plates on the toroid rib Supported via a 3 balls system Calibration: Ball triplets location on the plate measured with a 3D CMM (+- 10  m) Camera (Cf BCAMs calibration procedure in the end cap system) LED holes location w.r.t. balls known to <  m by construction CMOS camera Platform on MDT tubes

The barrel reference system6 Reference system implementation: BL-BS chambers connection BIL-BIS connection BML-BMS connection BOL-BOS connection Projective system

The barrel reference system7 Implementation on MDT chambers

The barrel reference system8 SIMULATION/RECONSTRUCTION (1): Principle of the simulation/reconstruction program: Mechanical elements (MDT chambers, sensor platform, reference plates) are simulated by a 3D nodes in space, connected by either rigid mechanical bars (fixed distance), by proximity sensors (distance measurement), by RASNIKs (sagitta measurement over 3 nodes) or camera/LED system (angular and distance measurements): A MDT chamber is described by 4 nodes at the corners + one central node, connected by rigid bars and RASNIKs (inplane). The 4 corner nodes also carry the praxial sensors, connected to other praxial nodes via axial RASNIKs and proximity measurements. The projective nodes and the reference system nodes are rigidly connected to the 4 MDT corner nodes. The reference frame is defined by 3 reference plate nodes (one is fixed, the second has 2 dof, the third only one dof). In the simulation, all nodes are moved in space with ranges [+- 5mm] in all 3 directions. The reconstruction algorithm is based on a global fit which accounts for all the nodes connections.

The barrel reference system9 Nodes layout in the simulation/reconstruction program (one sector) RASNIK Camera (BCAM) Plates on toroid ribs BIL BML BOL In-plane RASNIKs BOL BML BIL z y x y z x cm

The barrel reference system10 SIMULATION/RECONSTRUCTION (2): AXIAL RASNIK resolutions: 5  m in x/y, in magnification 100  rad on mask/pixel lines rotation CAMERA resolutions: 100  rad on absolute pointing direction 20  rad on relative spot angles (=> on distance measurement) PROXIMITY sensor resolutions: 20  m in x/y/z Precision on chamber NODE positioning: Praxial and projective nodes: 20  m in z/y, 150  m in x (tube direction) Reference system nodes : 200  m in x/y/z Precision on distance measurement between 2 plates on the same toroid coil: 100  m

The barrel reference system11 Reconstruction accuracy of the nodes corresponding to the toroid rib plates  x = 306  m  y = 216  m  z = 393  m   x = 117  rad   y = 99  rad   z = 76  rad cm rad TranslationsRotations

The barrel reference system12 Reconstruction accuracy of the nodes corresponding to the MDT corners  x = 321  m  y = 252  m  z = 482  m cm Translations Projective track sagitta reconstruction accuracy Generated  z = 4.5 mm  z = 20  m Reconstructed cm The measured position of a straight track hit in a chamber is calculated by interpolation w.r.t. the assumed positions of the 4 corner nodes. The generated sagitta results from the initial random nodes movements (supposed to be unknown).

The barrel reference system13 Conclusion: The proposed system provides the required accuracy on the absolute chamber positioning within a sector. The simulation/reconstruction study of the whole barrel system is yet to be performed. Status and planning: 05/2001: Final drawings of the MDT platforms (similar to the platform for the magnetic field sensors) and of the positioning tools (if required) 10/2001: Delivery to the MDT construction sites of the first platforms and of their positioning tools. 12/2001: first barrel MDT chambers build with reference platforms 2003: Assembly and calibration of the cameras 2003: Assembly and measurement of the reference plates. 2003: Construction of the LED supports 2003/2004: Assembly and calibration of the cameras for the BL-BS connections 2004: Installation on the toroid ribs before the chamber installation : Installation in the ATLAS cavern of the BL-BS extension plates with their cameras