The RICH detector of AMS-02: 5 years of operation in space

Abstract

AMS-02 is a high-energy particle physics magnetic spectrometer installed on the International Space Station since May 2011, and operating continuously since then. The AMS-02 Ring Imaging Čerenkov counter (RICH) is a specialised sub-detector for the precise measurement of the particle velocity β with a resolution of Δβ/β=0.7(2.4)×10−3 for helium nuclei passing through the Aerogel (NaF) radiator. From the emitted photon counting the particle absolute charge magnitude |Z| can be estimated with an uncertainty of 0.3 charge units for helium nuclei. In 5 years of operations the optical properties of the RICH had no significant degradation and the performances of the detector have been stable in time.By means of the simultaneous use of the Silicon Tracker and the RICH, AMS is able to investigate the isotopic composition of cosmic rays in the kinetic energy range from few GeV/n to ∼10GeV/n for elements with charge |Z| up to 4 with unprecedented statistics. The precise measurement of cosmic rays light nuclei isotopes ratio, such as 3He/4He and 10Be/9Be, provide important constraints to the free parameters in the models for cosmic rays propagation in our Galaxy. In particular the mass distinction between 3He and 4He needed for the measurement of the 3He/4He flux ratio is obtained by statistical methods. The excellent simulation of the AMS detector provides the precise description needed for this analysis. Moreover, the use of the geomagnetic field for selecting control samples of CRs with enhanced abundances of heavy isotopes provides an independent tool for the study of the light nuclei isotopic composition with AMS.