FAST: a compact scintillating fiber detector for antiproton cross section measurements

A novel tracking detector (FAST, Fiber Antiproton Scintillating Tracker) has been developed for the measurement of the annihilation cross section of slow antiprotons at the CERN Antiproton Decelerator. FAST has to reconstruct the charged pion tracks produced in the antiproton annihilation in gaseous and solid targets. The cylindrical (diameter: 30 cm, length: 50 cm) detector consists of 2 axial and 4 stereo layers of 1 mm BCF-10 scintillating \ufb01bers readout by 42 multianode photomultipliers (64 channels) whose signals are ampli\ufb01ed and discriminated by the VA64TAP2.1+LS64 VLSI ASICs and sampled at 320 MHz by a Cyclone II Altera FPGA. The fast sampling allows to distinguish annihilation events at the ns level as required by the pulsed nature of the AD beam (106 p in a 40 ns bunch for 6 bunches every 3c 110 s). \uaf The paper describes the detector design, its commissioning with cosmic rays and its performance in the 2007 data taking