Antiproton identification below threshold with AMS-02 RICH detector

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The Alpha Magnetic Spectrometer (AMS-02) was installed on the International Space Station (ISS) and it 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 them, 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. 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-rays data, e⁻ contamination can be well suppressed within 3% with β≈ 1, while keeping 76% efficiency for p below the threshold.