General Antiparticle Spectrometer

The General Antiparticle Spectrometer (GAPS) is the first experiment optimized to detect cosmic-ray antinuclei below 0.25 GeV/n as a signature of dark matter annihilation or decay in the Galaxy. Compared to other experimental handles for detecting dark matter, antideuterons provide a uniquely precise target: the expected astrophysical antideuteron background is orders of magnitude lower than the possible dark matter signal, such that a single antideuteron at this energy scale would be a smoking-gun signature of new physics. The GAPS program will also provide a precision antiproton spectrum in a previously unprobed low-energy range, as well as leading sensitivity to antihelium-3 nuclei. 

The GAPS scientific program is accessible thanks to a novel particle identification method based on exotic atom formation, de-excitation, and decay. Exotic atoms provide a unique handle for the negatively-charged antinuclei, facilitating excellent rejection of the positive-nucleus background. Meanwhile the method does not require a magnet, enabling a large sensitive area for rare events. With its large acceptance and orthogonal sources of systematic uncertainty compared to other experiments, GAPS will either make the first definitive detection of a cosmic-ray antideuteron or exclude the diverse dark matter models that would produce these particles.

Cartoon illustrating some of the theoretical considerations involved in determining the antideuteron flux at Earth due to dark matter. Dark matter particles annihilate (or decay) into Standard Model particles, of which some may form an antideuteron. Antideuterons then propagate through the galaxy, heliosphere, and upper atmosphere to GAPS.