Progress on Ultra-Heavy Cosmic-Ray Analysis with CALET on the International Space Station
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Date
2021-07-12
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Citation of Original Publication
“Progress on Ultra-Heavy Cosmic-Ray Analysis with CALET on the International Space Station,” W. V. Zober, B. F. Rauch, A. Ficklin, and N. Cannady for the CALET Collaboration, Proceedings of Science: 37th International Cosmic Ray Conference , (Berlin, Germany), 124 (2021). https://doi.org/10.22323/1.395.0124
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This work was written as part of one of the author's official duties as an Employee of the United States Government and is therefore a work of the United States Government. In accordance with 17 U.S.C. 105, no copyright protection is available for such works under U.S. Law.
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Abstract
The Calorimetric Electron Telescope (CALET), launched to the International Space Station in
August 2015 and continuously operating since, measures cosmic-ray (CR) electrons, nuclei and
gamma-rays. CALET utilizes its main calorimeter charge detector to measure CR nuclei from 1H
to 40Zr. In order to maximize the acceptance of the rare ultra-heavy (UH) CR above 30Zn, a special
high duty cycle (∼90%) UH trigger is used that does not require passage through the 27 radiation
length deep Total Absorption Calorimeter (TASC). This provides a 6× increase in geometry factor
allowing CALET to collect in 5 years a UHCR dataset with statistics comparable to those from
the first flight of the balloon-borne SuperTIGER instrument but without the need for atmospheric
corrections. Previous CALET UHCR analyses using time and position corrections based on 26Fe
and a geomagnetic vertical cutoff rigidity selection have shown abundances of even nuclei in
agreement with SuperTIGER. To further improve resolution and maximize statistics, a trajectory
dependent geomagnetic rigidity selection has been employed here with further work being done to
implement a Cash-Karp Runge-Kutta ray tracing method for an improved determination of effective
cutoff rigidities. Additional work has also been done to analyze events from the smaller dataset
of events that pass through the TASC, which provides energy information and a better charge
assignment that will provide higher resolution UH measurements, albeit with lower statistics.