A superconducting solenoidal spectrometer for a balloon-borne experiment

The BESS detector is a new type of balloon-borne spectrometer which utilize s various technologies recently developed for collider experiments. The pri ncipal scientific objectives include a measurement of cosmic-ray antiproton spectrum, search for anti-nuclei in cosmic radiation, and precise meaureme nts of cosmic-ray primaries. A thin superconducting solenoidal coil produce s a uniform magnetic field of 1 T. Cylindrical drift chambers are located i nside and outside the coil and perform continuous tracking. The momentum re solution is 0.5% at 1 GeV/c. i.e., the maximum detectable rigidity is 200 G V. Scintillation counter hodoscopes, placed above and below the solenoid, p rovide timing and dE/dx measurements and trigger generation. The timing res olution is 80 ps/counter. This cylindrical configuration achieves a large g eometrical acceptance of 0.35 m(2) sr which is essential to detect rare cos mic-ray particles. In order to cope with high trigger rate and large data s ize, intelligent trigger circuits and a fast and parallel data acquision sy stem are also developed. In 1993, the first scientific flight of the BESS a pparatus was carried out and the first mass-measured antiprotons were detec ted at energies below 500 MeV (C) 2000 Elsevier Science B.V. All rights res erved.