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Leptons with E>200 MeV trapped in the Earth's radiation belts

For the first time accurate measurements of electron and positron fluxes in the energy range 0.2-10 GeV have been performed with the Alpha Magnetic Spectometer (AMS) instrument at altitudes of 370-390 Km in the geographic latitude interval +/- 51.7 deg. We present an original analysis of the AMS data, focused on the study of the under-cutoff component of these fluxes, outside the region of the South Atlantic Anomaly (SAA). A separation in quasi-trapped, long lifetime (O(10 s)), and albedo, short life time (O(100 ms)), components is found. The flux maps as a function of the canonical adiabatic variables L, alpha0 are determined in the interval (L,alpha0)=(0.95-3,0-90) for electrons with E less than 10 GeV, and positrons with E less than 3 GeV. The results are compared with existing data at lower energies and in similar L, alpha0 range. The properties of the observed under-cutoff particles are also investigated in terms of their residence times and geographical origin. The resulting distributions are discussed and related to the characteristics of the drift shells observed by AMS.