  The General Antiparticle Spectrometer (GAPS) is designed to carry out
indirect dark matter search by measuring low-energy cosmic-ray antiparticles.
Below a few GeVs the flux of antiparticles produced by cosmic-ray collisions
with the interstellar medium is expected to be very low and several
well-motivated beyond-standard models predict a sizable contribution to the
antideuteron flux. GAPS is planned to fly on a long-duration balloon over
Antarctica in the austral summer of 2020. The primary detector is a 1m3 central
volume containing planes of Si(Li) detectors. This volume is surrounded by a
time-of-flight system to both trigger the Si(Li) detector and reconstruct the
particle tracks. The detection principle of the experiment relies on the
identification of the antiparticle annihilation pattern. Low energy
antiparticles slow down in the apparatus and they are captured in the medium to
form exotic excited atoms, which de-excite by emitting characteristic X-rays.
Afterwards they undergo nuclear annihilation, resulting in a star of pions and
protons. The simultaneous measurement of the stopping depth and the dE/dx loss
of the primary antiparticle, of the X-ray energies and of the star
particle-multiplicity provides very high rejection power, that is critical in
rare-event search. GAPS will be able to perform a precise measurement of the
cosmic antiproton flux below 250 MeV, as well as a sensitive search for
antideuterons.
