Search for anti-particles of cosmic origin with a superconducting spectrometer

A Balloon Experiment with Superconducting Spectrometer (BESS) to search for primordial anti-matter abundance in cosmic radiation and to measure anti-proton spectrum is being prepared. A large geometry factor of 1.2 m2sr was achieved by the solenoidal detector configuration. The magnet provides an uniform magnetic field of 1.2 tesla over a cylindrical volume of 0.85m in diameter and 1.0m in length. Anti-helium nuclei will be searched for to a level of anti-He/He∼10−8 and the low energy primary anti-proton flux will be observed down to anti-proton/proton∼10−6. The superconducting magnet has been constructed and excited to 1 tesla and showed good and stable performance. The main tracking device, jet type drift chamber, together with the readout electronics and data acquisition system have been assembled and tested. A flight to test the detector performance at the balloon altitude was successfully carried out in September 1989.