The General Antiparticle Spectrometer (GAPS) Antarctic Balloon Payload

TL;DR

GAPS is a balloon mission designed to detect low-energy cosmic-ray antinuclei as dark matter signatures using a novel detection technique and specialized instrumentation, successfully flown for 25 days.

Contribution

The paper introduces the design, integration, and successful flight of the GAPS payload with innovative particle detection and thermal management systems.

Findings

GAPS achieved 25 days of Antarctic balloon flight.

The payload successfully detected antinuclei signatures.

A new heat pipe system improved thermal efficiency.

Abstract

The General Antiparticle Spectrometer (GAPS) is an Antarctic stratospheric balloon mission designed to provide unmatched sensitivity to low-energy (<0.25 GeV/n) cosmic-ray antiprotons, antideuterons, and antihelium nuclei as signatures of dark matter. The distinctive GAPS particle identification technique relies on measuring the energy loss along the track of an incoming antinucleus as it slows down and is captured into an exotic atom, and then detecting the de-excitation X-rays and the nuclear annihilation products. This measurement is realized using a Tracker composed of more than 1000 custom silicon strip detectors and a plastic scintillator time-of-flight (TOF) system instrumenting more than 40m$^2$. Together, these subsystems provide the velocity and energy resolution, stopping power, particle tracking, and X-ray identification necessary to distinguish rare antinucleus signals from the abundant positive-nucleus backgrounds, all within the constraints of a high-altitude mission. A multi-loop capillary heat pipe system has been developed to maintain the tracker operating temperature with significant mass and power savings over a conventional pump-based system. The first GAPS science payload flew for 25 days during the 2025/26 NASA Antarctic balloon campaign. We detail the design, integration, and commissioning of the payload prior to flight.