Precision measurement of nuclei in cosmic rays with the alpha magnetic spectrometer on the International Space station

Abstract

AMS-02 is wide acceptance high-energy physics experiment installed on the International Space Station in May 2011 and operating continuously since then. With a collection rate of approximately 1.7×1010 events/year, and the combined identification capabilities of 5 independent detectors, AMS-02 is able to precisely separate cosmic rays light nuclei (1 ≤Z ≤ 8). Knowledge of the precise rigidity dependence of the light nuclei fluxes is important in understanding the origin, acceleration, and propagation of cosmic rays. AMS-02 collaboration has recently released the precise measurements of the proton and helium fluxes as function of rigidity (momentum/charge). The spectral indexes of both fluxes progressively hardens at rigidities larger than 100 GV. The rigidity dependence of the helium flux spectral index is similar to that of the proton spectral index though the magnitudes are different. Remarkably, the spectral index of the proton to helium flux ratio increases with rigidity up to 45 GV and then becomes constant; i.e. the flux ratio above 45 GV is well described by a single power law. Preliminary results about the spectral shape of other light nuclei have been shown during the conference and are here briefly introduced.