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

Fabrication of low-cost, large-area prototype Si(Li) detectors for the GAPS experiment

A Si(Li) detector fabrication procedure has been developed with the aim of satisfying the unique requirements of the GAPS (General Antiparticle Spectrometer) experiment. Si(Li) detectors are particularly well-suited to the GAPS detection scheme, in which several planes of detectors act as the target to slow and capture an incoming antiparticle into an exotic atom, as well as the spectrometer and tracker to measure the resulting decay X-rays and annihilation products. These detectors must provide the absorption depth, energy resolution, tracking efficiency, and active area necessary for this technique, all within the significant temperature, power, and cost constraints of an Antarctic long-duration balloon flight. We report here on the fabrication and performance of prototype 2"-diameter, 1-1.25 mm-thick, single-strip Si(Li) detectors that provide the necessary X-ray energy resolution of $\sim$4 keV for a cost per unit area that is far below that of previously-acquired commercial detectors. This fabrication procedure is currently being optimized for the 4"-diameter, 2.5 mm-thick, multi-strip geometry that will be used for the GAPS flight detectors.Comment: Accepted for publication at Nuclear Instrumentation and Methods A, 12 pages, 11 figure