We report progress in developing a novel antimatter detection scheme. The gaseous antiparticle spectrometer (GAPS) identifies antimatter through the characteristic X-rays emitted by antimatter when it forms exotic atoms in gases. The approach provides large area and field of view, and excellent background rejection capability. If the GAPS concept is successfully demonstrated, then it would be an ideal candidate for space-based, indirect dark matter searches. GAPS can detect antideuterons produced in neutralino annihilations. A modest GAPS experiment can detect the neutralino for all minimal SUSY models in which the neutralino mass is in the ∼ 50-350 GeV mass range. Underground searches, by contrast, are only sensitive to about 1/2 the SUSY parameter space in this mass range.

Abstract--Recent events highlight the increased risk of a terrorist attack using either a nuclear or a radiological weapon. One of the key needs to counter such a threat is long-range detection of nuclear material. Theoretically, gamma-ray emissions from such material should allow passive detection to distances greater than 100 m. However, detection at this range has long been thought impractical due to fluctuating levels of natural background radiation. These fluctuations are the major source of uncertainty in detection and mean that sensitivity cannot be increased simply by increasing detector size. Recent work has shown that this problem can be overcome through the use of imaging techniques. In this paper we describe the background problems, the advantages of imaging and the construction of a prototype, large-area (0.57 m 2 ) gamma-ray imager to detect nuclear materials at distances of ~100 m.

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.

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Abstract:We report on recent accelerator testing of a prototype general antiparticle spectrometer (GAPS). GAPS is a novel approach for indirect dark matter searches that exploits the antideuterons produced in neutralino-neutralino annihilations. GAPS captures these antideuterons into a target with the subsequent formation of exotic atoms. These exotic atoms decay with the emission of X-rays of precisely defined energy and a correlated pion signature from nuclear annihilation. This signature uniquely characterizes the antideuterons. Preliminary analysis of data from a prototype GAPS in an antiproton beam at the KEK accelerator in Japan has confirmed the multi-X-ray/pion star topology and indicated X-ray yields consistent with prior expectations. Moreover our success in utilizing solid rather than gas targets represents a significant simplification over our original approach and offers potential gains in sensitivity through reduced dead mass in the target area.The general antiparticle spectrometer (GAPS) is a novel concept for detection of antimatter. As described below it is particularly well suited for antideuteron searches. Antideuterons provide an indirect signature of neutralino annihilation, as first pointed out by Donato and collaborators [1], and a direct signature of black hole evaporation [2]. The operating principles, designs and sensitivity calculations for potential balloon and satellite-based GAPS experiments have been previously reported in Mori et al. [3], but the GAPS concept has not hitherto been demonstrated in a working prototype. We report here interim progress on analyzing a GAPS prototype exposed to an antiproton beam, as well as various beams representative of cosmic backgrounds, at the KEK accelerator facility in Japan. After a discussion of the use of antimatter in dark matter and primordial black hole searches, we briefly summarize recent theoretical studies of antideuteron searches and their relevance to our ongoing experimental program. We then follow with a description of the GAPS concept, the GAPS prototype experiment and analysis and plans for continued experimental work. We note that our preliminary analysis suggests that the GAPS concept is at least as promising as our previous simulations suggested, and thus recent theoretical analyses based on reference [3] remain unaltered by the current experimental landscape.