ONLINE ANALYSIS FOR THE OBELIX DRIFT CHAMBERS AT LEAR

We report on the characteristics and performances of front-end electronics and a data acquisition system for the jet drift chambers of the OBELIX experiment (PS201), installed at the LEAR facility of CERN. The signals of the chambers are digitized by 100 MHz 8-bit nonlinear FADCs readout through a VME-based tree-like acquisition chain. Data reduction and saving of off-line reconstruction time is obtained through zero suppression and by means of 80 embedded digital signal processors, which provide the drift time, the z-coordinate and the dE/dx sample information. With minimum ionizing particles we achieve a resolution of 160 mum in the r-phi plane and of 0.8% in the z-coordinate, and a double hit separation of about 2 mm. Preliminary results on dE/dx resolution are: sigma/mean = 12% and pi/K separation up to 500 MeV/c.