Abstract
GAPS (General Anti-Particle Spectrometer) is a balloon-borne experiment designed to measure low-energy (<0.25 GeV/n) cosmic antinuclei (i.e., antiprotons, antideuterons, and antihelium nuclei) as a signature of dark matter annihilation or decay. According to viable beyond-the-Standard Model theories, the predicted dark matter signal in the low-energy antideuterons and antihelium nuclei channels is several orders of magnitude higher than the astrophysical background. The experiment will conduct a series of at least three long-duration balloon flights at high altitudes from Antarctica. The instrument is composed of a Si(Li) tracker surrounded by a Time-of-Flight system made of plastic scintillators. GAPS uses the novel exotic-atom detection technique in which an antinucleus is captured by the tracker material and forms an exotic atom. This excited exotic atom decays within the order of nanoseconds emitting X-rays at specific energies defined by the atomic transitions and annihilates emitting secondary particles (mainly pions and protons). The measured quantities (e.g., dE/dx, time of flight, annihilation vertex position, X-rays energies, etc.) allow for identifying antinuclei with high precision.