FINAL RESULTS OF AN EXPERIMENTAL-STUDY OF A LARGE-AREA PLANAR DRIFT CHAMBER FILLED WITH A HE-BASED MIXTURE

This paper reports the final results of an accurate and complete exper imental study of the performance of a large-area (1150 x 566 mm(2)) pl anar drift chamber filled with a He-iC(4)H(10) (70%-30%) mixture, Sixt een chambers of this type will constitute the elements of the central part of the tracking device of FINUDA, one of the two spectrometers ap proved for running at DA Phi NE. The measured spatial resolution acros s the full drift cell ranges from 80 to 120 mu m for particles at norm al incidence angle, and the measured spatial resolution along the sens e wire, as measured by the charge division method, was better than 1% of the wire length, Efficiency, space-time relationship, long term sta bility and Lorentz angle were measured as well. Particular care was de voted to the study of the spatial resolution as a function of the inci dence angle, The conclusion of this study is that the chamber performa nces are the same or better than those obtained with Ar-based mixtures .