The fluxes of sub--cutoff particles detected by AMS, the cosmic ray albedo and atmospheric neutrinos

Abstract

New measurements of the cosmic ray fluxes (p, e+, e- and Helium) performed by the Alpha Magnetic Spectrometer (AMS) during a ten days flight of space shuttle have revealed the existence of significant fluxes of particles below the geomagnetic cutoff. These fluxes exhibit a number of remarkable properties, such as a He-3/He-4 ratio of order ~10, an e+/e- ratio of order ~4 and production from well defined regions of the Earth that are distinct for positively and negatively charged particles. In this work we show that the natural hypothesis, that these subcutoff particles are generated as secondary products of primary cosmic ray interactions in the atmosphere can reproduce all the observed properties. We also discuss the implications of the subcutoff fluxes for the estimate of the atmospheric neutrino fluxes, and find that they represent a negligibly small correction. On the other hand the AMS results give important confirmations about the assumption of isotropy for the interplanetary cosmic ray fluxes also on large angular scales, and on the validity of the geomagnetic effects that are important elements for the prediction of the atmospheric neutrino fluxes.