  The General Antiparticle Spectrometer (GAPS) will carry out a sensitive dark
matter search by measuring low-energy ($\mathrm{E} < 0.25
\mathrm{GeV/nucleon}$) cosmic ray antinuclei. The primary targets are
low-energy antideuterons produced in the annihilation or decay of dark matter.
At these energies antideuterons from secondary/tertiary interactions are
expected to have very low fluxes, significantly below those predicted by
well-motivated, beyond the standard model theories. GAPS will also conduct
low-energy antiproton and antihelium searches. Combined, these observations
will provide a powerful search for dark matter and provide the best
observations to date on primordial black hole evaporation on Galactic length
scales.
  The GAPS instrument detects antinuclei using the novel exotic atom technique.
It consists of a central tracker with a surrounding time-of-flight (TOF)
system. The tracker is a one cubic meter volume containing 10 cm-diameter
lithium-drifted silicon (Si(Li)) detectors. The TOF is a plastic scintillator
system that will both trigger the Si(Li) tracker and enable better
reconstruction of particle tracks. After coming to rest in the tracker,
antinuclei will form an excited exotic atom. This will then de-excite via
characteristic X-ray transitions before producing a pion/proton star when the
antiparticle annihilates with the nucleus. This unique event topology will give
GAPS the nearly background-free detection capability required for a rare-event
search.
  Here we present the scientific motivation for the GAPS experiment, its design
and its current status as it prepares for flight in the austral summer of
2021-22.
