Antiproton identification below threshold with the AMS-02 RICH detector

Abstract：

The Alpha Magnetic Spectrometer (AMS-02), which is installed on the International Space Station (ISS), has been collecting data successfully since May 2011. The main goals of AMS-02 are the search for cosmic anti-matter, dark matter and the precise measurement of the relative abundance of elements and isotopes in galactic cosmic rays. In order to identify particle properties, AMS-02 includes several specialized sub-detectors. Among these, the AMS-02 Ring Imaging Cherenkov detector (RICH) is designed to provide a very precise measurement of the velocity and electric charge of particles. We describe a method to reject the dominant electron background in antiproton identification with the use of the AMS-02 RICH detector as a veto for rigidities below 3 GV. A ray tracing integration method is used to maximize the statistics of p with the lowest possible e^- background, providing 4 times rejection power gain for e^- background with respect to only 3% of p signal efficiency loss. By using the collected cosmic-ray data, e^- contamination can be well suppressed within 3% with β ≈ 1, while keeping 76% efficiency for p below the threshold.