Test of a full scale sector for a 1 m long high resolution vertex chamber

We have tested a 1 m long prototype sector consisting of 170 rectangular drift cells. The sector is arranged in 25 radial layers, of which the 13 inner layers have cell sizes of 10 mm x 15 mm and the 12 outer layers of 14 mm x 21 mm. To measure the coordinates of a track along the wire, 13 axial layers are interleaved with 12 stereo layers. Special care was taken to keep cell sizes as homogeneous as possible to obtain the same space vs drift-time relation for all layers of the same cell size. A low diffusion gas mixture of 85% CO2 plus 15% isobutane was used in a closed loop gas system, including a purifier, run at an absolute pressure of 1 and 2 bar and stabilized within a few mbars by a microprocessor system. The chamber signals were read-out with TDCs. In the central part of the drift length we achieved space resolutions of 35 μm per cell at atmospheric pressure and of 25 μm per cell at 2 bar pressure. These figures correspond to axial resolutions of 0.5 to 1 mm per stereo layer. (orig.)