FAST: a scintillating fiber tracker for antiprotons annihilation detection

A new fiber detector has been developed for the measurement of the annihilation cross-section of slow antiprotons (5 MeV for the 2006 run, < 1 keV in 2007) in gaseous targets in the framework of the ASACUSA experiment at the AD Antiproton Decelerator at CERN. The cylindrical gaseous target, 10 cm in radius, is surrounded by 2 axial and 4 stereo scintillating fiber layers built with 1 mm BCF-10 fibers from Bicron. The scintillation light released by charged pions originating in the annihilation vertex is readout by 64 channel multianode PMTs produced by HAMAMATSU. The anode outputs are amplified and discriminated with VLSI ASICs manufactured by IDEAS (VA64TAP2.1) and then sampled with a 320 MHz clock in order to extract the hit and time information by a set of ALTERA FPGAs. The paper describes the detector assembly, the custom electronics readout chain and the results of the tests during,the commissioning phase.