A 18m(2) cylindrical tracking detector made of 2.6m long, stereo mylar straw tubes with 100 mu m resolution

An array of 2424 2.6 m-long, 15 mm-diameter mylar straw tubes, arranged in two axial and four stereo layers, has been assembled. The array covers a cy lindrical tracking surface of 18 m(2) and provides coordinate measurement i n the drift direction and along the wire. An under-standing of the systemat ic effects which are introduced by gravitational sag and electrostatics, th us dominating the detector performance especially with long straws, allows to determine wire position from drift-time distribution. The correction has been applied to reach a space resolution of 40 mu m with DME, 100 mu m wit h Ar + C2H6, and 100-200 mu m with CO2. Such a resolution is the best ever obtained for straws of these dimensions. A study of the gas leakage for the straw system has been performed, and results are reported. The array is be ing commissioned as a subdetector of the FINUDA spectrometer, and tracking performances are being studied with cosmic rays. (C) 1998 Elsevier Science B.V. All rights reserved.