Results of the AMS experiment

The Alpha Magnetic Spectrometer (AMS) was flown in June 1998 on the space shuttle Discovery during flight STS-91 in a 51.7◦ orbit at altitudes between 320 and 390 km. The major detector elements were a permanent magnet with an analyzing power B∗L2 of 0.14 Tm2, a six-layer, double-sided silicon tracker, time-of-flight hodoscopes, a ˇCerenkov counter and anti-coincidence counters. A total of 2.86 × 106 He nuclei were observed in the rigidity range 1 to 140 GeV. No He nuclei were detected at any rigidity. The upper limit on the flux ratio of He to He is 1.1×10−6. The proton spectrum in the kinetic energy range 0.1 to 200 GeV was measured, and is parameterized by a power law above the geomagnetic cutoff. Below the geomagnetic cutoff, a substantial second spectrum was observed concentrated at equatorial latitudes with a flux of ∼70m−2s−1sr−1. The lepton spectra in the kinetic energy ranges 0.2 to 40 GeV for electrons and 0.2 to 3 GeV for positrons were measured. Two distinct spectra were observed, a higher energy spectrum and a substantial second spectrum with positrons much more abundant than electrons. Tracing leptons from the second spectra shows that most of these leptons travel for an extended period of time in the geomagnetic field and that the positrons and electrons originate from two complementary geographic regions. Long-lived secondary spectra protons (antiprotons) originate from the same regions as positrons (electrons)