Identification of Light Cosmic-Ray Nuclei with AMS-02

Abstract

AMS-02 is a wide acceptance (0.5 m2 sr) and long duration (up to 20 years) magnetic spectrometer operating onboard the International Space Station since May 2011. Its main scientific objectives are the indirect research of Dark Matter, searches of primitive Anti-Matter and the precise measurement of the Cosmic-Ray (CR) spectra. Among charged CR species, AMS-02 will be able to measure relative abundances and absolute fluxes of CRs nuclei from Hydrogen up to at least Iron (Z = 26) in a kinetic energy range from hundreds MeV to TeV per nucleon. The high statistics measurement of the chemical composition of CRs in this extended energy range will reveal new insights about the CRs life in the Galaxy, from their origin to the propagation in the interstellar medium, giving new constraints to astrophysical models of Galactic CRs. The nucleus absolute charge, Z, is measured several times along the trajectory of the particle inside AMS-02 using different detection techniques: in the 9 planes of the Silicon Tracker, in the 4 layers of scintillator counters of the Time-of-Flight system (TOF), in the Ring Imaging Cherenkov Counter (RICH) as well as in the 20 layers of Transition Radiation Detector (TRD) and in the upper layers of the Electromagnetic Calorimeter (ECAL). The combination of the redundant measurements delivered by the tracking system and by the TOF allows an accurate discrimination between chemical elements. The charge measurements in the detectors on top of AMS, as the Upper plane of the Tracker and in TRD, is used for the identification of the incoming nuclear specie and allows the charge-changing events background estimation. The AMS-02 different charge measurement principles are here briefly explained, and performance of each sub-detector presented. Then the AMS-02 combined charge separation capability as well as the interaction events identification principles are presented.