On-line 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 μm in the r-θ 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: σ mean = 12% and π K separation up to 500 MeV/c.