A 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 the
indirect dark matter search that exploits cosmic antideuterons. 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. In
anticipation of a future balloon experiment, an accelerator test was conducted
in 2004 and 2005 at KEK, Japan, in order to prove the concept and to precisely
measure the X-ray yields of antiprotonic exotic atoms formed with different
target materials [1]. The X-ray yields of the exotic atoms with Al and S
targets were obtained as ~ 75%, which are higher than were previously assumed
in [2]. A simple, but comprehensive cascade model has been developed not only
to evaluate the measurement results but also to predict the X-ray yields of the
exotic atoms formed with any materials in the GAPS instrument. The cascade
model is extendable to any kind of exotic atom (any negatively charged
cascading particles with any target materials), and it was compared and
validated with other experimental data and cascade models for muonic and
antiprotonic exotic atoms. The X-ray yields of the antideuteronic exotic atoms
are predicted with a simple cascade model and the sensitivity for the GAPS
antideuteron search was estimated for the proposed long duration balloon
program [3], which suggests that GAPS has a strong potential to detect
antideuterons as a dark matter signature. A GAPS prototype flight (pGAPS) was
launched successfully from the JAXA/ISAS balloon facility in Hokkaido, Japan in
summer 2012 [4, 5] and a proposed GAPS science flight is to fly from Antarctica
in the austral summer of 2017-2018.
