Iterative-Bayesian unfolding of cosmic-ray isotope fluxes measured by AMS-02

Abstract

The measurement of the isotopic composition of cosmic rays (CRs) provides essential insights into the understanding of the origin and propagation of these particles, namely the CR source spectra, the propagation processes and the galactic halo size. The Alpha Magnetic Spectrometer (AMS-02), a CR experiment operating aboard the International Space Station since May 2011, has the capability of performing these measurements due to its precise determination of the velocity provided by its Time of Flight (TOF) and Ring Imaging Cherenkov (RICH) detectors. The correct interpretation of the data requires the measurements to be deconvoluted from the instrumental effects. The unique design of AMS-02, with more than one detector being used to measure the same particle flux, requires a novel approach to unfold the measured fluxes. In this work, we apply for the first time the so-called iterative-bayesian approach in the context of the direct measurement of the cosmic-ray fluxes. Moreover, we introduce a non-parametric regularization method for the detector response functions and a single, smooth flux prior covering the range of measurements from both detectors, TOF and RICH. The accuracy of the method is assessed using a simulated flux based on previous AMS-02 measurements and taking into account the full detector response. In addition, the estimation of the errors and a discussion about the performance of the method are also shown, demonstrating that the method is fast and reliable, allowing for the recovery of the true particle fluxes in the whole energy range.