An Accelerator Measurement of Atomic X-ray Yields in Exotic Atoms and Implications for an Antideuteron-Based Dark Matter Search

The General AntiParticle Spectrometer (GAPS) is a novel approach for indirect dark matter searches that exploits cosmic antideuterons. The low energy antideuteron provides a clean dark matter signature, since the antideuteron production by cosmic ray interactions is suppressed at low energy, while the WIMP-WIMP annihilation can produce low energy an- tideuterons. GAPS utilizes a distinctive detection method using atomic X-rays and charged particles from the exotic atom as well as the timing, stopping range and dE/dX energy deposit of the incoming particle, which provides excellent antideuteron identification. Prior to the future balloon experiment, an accelerator test was conducted in 2004 and 2005 at KEK, Japan to measure the atomic X-rays of antiprotonic exotic atoms produced by different targets. In 2005, solid targets were tested to avoid the bulky fixture of the gas target and also to have flexibility of the detector geometry in the flight experiment. Recently, we have developed a simple cascade model and the parameters were fitted with the experimental results. The cascade model was extended to the antideuteronic exotic atom for the GAPS flight experiment. GEANT4 simulation was conducted to obtain optimized cuts on the timing, stopping range, dE/dX energy deposit, atomic X-rays, and annihilation products, in order to eliminate the background. Based on the simulation results, we have estimated the GAPS sensitivity with the antideuteron flux. GAPS has a strong potential to detect a dark matter signature.