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T: Teilchenphysik

T 209: Spurkammern I

T 209.4: Vortrag

Freitag, 4. März 2005, 14:45–15:00, TU H3025

Magnetic Field Dependence of the Response of the ATLAS Muon Drift-Tube Chambers — •Ch. Valderanis¹, J. Dubbert¹, S. Horvat¹, D. Kharatchenko¹, O. Kortner¹, S. Kotov¹, H. Kroha¹, K. Nikolaev¹, F. Rauscher², R. Richter¹, and A. Staude² — ¹Max-Planck-Insitut für Physik, Föhringer Ring 6, D-80805 München — ²Sektion Physik der Ludwig-Maximilians-Universität München, Am Coulombwall, D-85748 Garching

In the ATLAS muon spectrometer drift-tube chambers are used as precision tracking detectors in a 0.4 T magnetic field generated by superconduction air toroid coils. The chambers consist of aluminium drift tubes with 30 mm diameter, 0.4 mm thick Aluminium walls, and sense wires of 50 µm diameter. The tubes are filled with an Ar:CO₂ (93:7) mixture at an absolute pressure of 3 bar and operated at a voltage of 3080 V corresponding to a gas gain of 2·10⁴. Under these conditions, a chamber resolution of 40 µm is achieved provided that the space-to-drift-time relationship r(t) is known with 20 µm accuracy. The component of the magnetic field along the sense wires of the drift tubes varies by up to 0.4 T in some chambers at the end of the magnetic coils. As the Lorentz force bends the electrons drifting to the anode wires, the r−t relationship is altered by the magnetic field along the tubes. In order to ensure an r−t relationship with the required accuracy, the magnetic field dependence of the r−t relationship has to be corrected for. The talk presents results of test-beam measurements of this effect and confronts them with expectations from a Garfield simulation.