The General Antiparticle Spectrometer (GAPS) Antarctic Balloon Payload

The GAPS Collaboration, Kazutaka Aoyama, Tsuguo Aramaki, Padrick Beggs, Mirko Boezio, Steven E. Boggs, Valter Bonvicini, Gabriel Bridges, Donatella Campana, Scott Candey, William W. Craig, Philip von Doetinchem, Conor Earley, Erik Everson, Lorenzo Fabris, Sydney Feldman, Hideyuki Fuke, Florian Gahbauer, Cory Gerrity, Luca Ghislotti, Charles J. Hailey, Takeru Hayashi, Akiko Kawachi, Kai Konoma, Masayoshi Kozai, Paolo Lazzaroni, Alexander Lowell, Massimo Manghisoni, Matteo Martucci, Keita Mizukoshi, Emiliano Mocchiutti, Brent Mochizuki, Kazuoki Munakata, Riccardo Munini, Shun Okazaki, Jerome Olson, Rene A. Ong, Giuseppe Osteria, Francesco Palma, Kaliroë Pappas, Kerstin Perez, Francesco Perfetto, Lodovico Ratti, Valerio Re, Elisa Riceputi, Brandon Roach, Field R. Rogers, Nathan Saffold, Suzuto Sakamoto, Pratiksha Sawant, Valentina Scotti, Yuki Shimizu, Roberta Sparvoli, Achim Stoessl, Arathi Suraj, Alessio Tiberio, Grace Tytus, Elena Vannuccini, Sarah Vickers, Luigi Volpicelli, Zhen Wu, Mengjiao Xiao, Jinghe Yang, Kelsey Yee, Tetsuya Yoshida, Gianluigi Zampa, Jiancheng Zeng, Jeffrey Zweerink

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.