Gas pixel chambers

Gas pixel (pad) chambers are proposed to be used in the HERA-B experiment in the inner parts of both the high-p(t) pretrigger system and the muon system. The first prototypes have been built and successfully tested at ITEP, Moscow. An efficiency of 99.87% has been attained with a gas amplification of 10(4). A chamber with 10 x 10 mm(2) cells, filled with the gas mixture Ar/CF4 (80/20), allows detection of more than 99% of all particles within 80 ns. Stable operation was achieved with beam intensities of 3 x 10(5) particles/cm(2)/s without any visible degradation of the performance. Crosstalk between neighboring cells was studied and was found to be not larger than 1.5% and caused by delta-electrons.