Integration and Calibration of the GAPS Antarctic Balloon Payload

With its inaugural Antarctic long-duration balloon mission in December 2024, the General Antiparticle Spectrometer (GAPS) will become the first experiment optimized to detect cosmic-ray antinuclei below 0.25 GeV/n. Detection of a single antideuteron in this energy range would be a smoking-gun signature of new physics, such as dark matter. 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. This new parameter space is accessible thanks to a novel particle identification method based on exotic atom formation, de-excitation, and annihilation. The method provides a unique signature for the negatively-charged antinuclei, facilitating excellent rejection of the positive-nucleus background, and does not require a magnet, enabling a large sensitive area for rare events. The GAPS instrument is designed to provide excellent discrimination power for rare events within the power and mass constraints of a long-duration balloon. The time-of-flight, composed of 160 scintillator paddles, provides the system trigger as well as the GAPS energy scale. The 2.5 m³ tracker volume is instrumented with 10-cm-diameter silicon sensors, which serve as the target, X-ray spectrometer, and particle tracker. Together, a large-area radiator and an integrated oscillating heat pipe system cool the payload without a bulky cryostat. This contribution reports the integration and calibration of the GAPS science payload, including the performance of the sensitive detector subsystems, the cooling system, the power distribution, and data acquisition and onboard event processing.