The FAST detector, installed on the beam line of the antiproton decelerator at CERN in the framework of the ASACUSA Collaboration, is dedicated to the measurement of the annihilation cross-section of slow antiprotons (with an energy below 5 MeV, corresponding to a momentum of 100 MeV/c) in solid and gaseous targets. The goal of the detector is to reconstruct the tracks of the charged pions generated in the annihilation to identify and count the annihilation vertices. The detector has a cylindrical geometry and is made of 2 axial fiber layers and 4 stereo fiber layers. More than 10 km of BCF-10 fibers by Bicron with a 1 mm diameter and a 70 cm length have been used. To obtain a high efficiency reducing the dead areas each fiber layer is made of two staggered half layers, in a doublet ribbon configuration. The scintillating light is detected by 42 multianode photomultipliers (HAMAMATSU H7546) with 64 channels each; given that 4 fibers are readout by a single PMT anode, the total nuber of electronic channels is similar to 2500. The signals from the PMTS are amplified, shaped and discriminated by a pair of ASICs (VA64TAP2.1 and LS64-2 from IDEAS) and then sent to a FPGA (Altera Cyclone 11) that performs a 640 MHz digital sampling, allowing to measure the arrival time of the signal of each hit fiber in a 800 ns time window, as requested by the time structure of the antiproton decelerator beam. This paper describes the detector and its electronics, reports the results of the cosmic-ray run during the commissioning phase and the preliminary results of the 2007 data taking at the antiproton decelerator.
FAST: A scintillating fiber detector for antiproton cross-section measurements at the antiproton decelerator
Mascacna V.;PREST, MICHELA;
2007-01-01
Abstract
The FAST detector, installed on the beam line of the antiproton decelerator at CERN in the framework of the ASACUSA Collaboration, is dedicated to the measurement of the annihilation cross-section of slow antiprotons (with an energy below 5 MeV, corresponding to a momentum of 100 MeV/c) in solid and gaseous targets. The goal of the detector is to reconstruct the tracks of the charged pions generated in the annihilation to identify and count the annihilation vertices. The detector has a cylindrical geometry and is made of 2 axial fiber layers and 4 stereo fiber layers. More than 10 km of BCF-10 fibers by Bicron with a 1 mm diameter and a 70 cm length have been used. To obtain a high efficiency reducing the dead areas each fiber layer is made of two staggered half layers, in a doublet ribbon configuration. The scintillating light is detected by 42 multianode photomultipliers (HAMAMATSU H7546) with 64 channels each; given that 4 fibers are readout by a single PMT anode, the total nuber of electronic channels is similar to 2500. The signals from the PMTS are amplified, shaped and discriminated by a pair of ASICs (VA64TAP2.1 and LS64-2 from IDEAS) and then sent to a FPGA (Altera Cyclone 11) that performs a 640 MHz digital sampling, allowing to measure the arrival time of the signal of each hit fiber in a 800 ns time window, as requested by the time structure of the antiproton decelerator beam. This paper describes the detector and its electronics, reports the results of the cosmic-ray run during the commissioning phase and the preliminary results of the 2007 data taking at the antiproton decelerator.
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