Development of a 150 000 channel MSGC tracking system for the experiment HERA-B

The universities of Heidelberg, Siegen and Zürich11Members of the collaboration are: T. Beckmann, C. Bresch, H.-B. Dreis, F. Eisele, S. Feuerstack, S. Hausmann, A. Hölscher, T. Hott, A. Lange, A. Maag, V. Myalitsin, P. Robmann, B. Schmidt, S. Schmidt, S. Steiner, U. Straumann, P. Truöl, S. Visbeck, A.-H. Walenta, T. Walter, U. Werthenbach, G. Zech and T. Zeuner. reparing the inner tracker of the HERA-B experiment at DESY designed to measure CP violation in B meson decays. The system consists of 200 MSGC chambers of sizes up to 30 × 30 cm2 with a total of 150 000 electronic channels. Rates up to 104 s−1 mm−2 have to be handled. The gold electrodes (300 μm pitch) are produced by a lift-off process on an alkali-free glass (300 μm thick). The glass is CVD coated with amorphous carbon with a surface resistivity of 1014ω/□. It provides the required lifetime of 5 years with an integrated charge of 30 mC per cm of the anode length. Gains > 5000 are obtained. The efficiency is greater than 99% with negligible noise rate. Measures to avoid deterioration of the anodes by discharges caused by heavy ionizing particles are discussed. GC detectors are connected to hybrid electronics via Kapton foils. A special bonding machine has been built which allows the adjustment by a video system and the chariots moved by micrometer screws and contains electronically steered glue dispenser and pressure pistons.