The alignment of the L3 forward-backward muon chambers at LEP200

In order to meet the detection requirements of LEP200, the L3 muon spectrometer was extended to cover the angular range of 44° > θ > 24°, where θ denotes the polar angle. The new system installed consists of three layers of drift chambers attached to the doors returning the flux of the L3 magnetic field. This note is describes in detail the alignment system, relating the central detector to the closest layer of the added forward-backward system as well as the relative alignment between its three layers. The achieved alignment resolutions are 70 μm in x, 150 μm in y, and 580 μm in z, for the link between the central detector and the closest forward-backward layer. For the relative alignment of the three layers 50 μm in x and y, and 200 μm in z are reached.