Measurement of the Iron Spectrum in Cosmic Rays from 10 GeV$/n$ to 2.0 TeV$/n$ with the Calorimetric Electron Telescope on the International Space Station

TL;DR

This paper presents a precise measurement of the cosmic-ray iron spectrum from 10 GeV/n to 2 TeV/n using CALET on the ISS, confirming a power-law behavior consistent with previous experiments.

Contribution

First precise measurement of the cosmic-ray iron spectrum over a wide energy range with space-based instrumentation, extending previous observations with improved accuracy.

Findings

The iron spectrum follows a single power law with index -2.60 ± 0.03 from 50 GeV/n to 2 TeV/n.

Results are consistent with previous experiments within errors.

The study demonstrates CALET's capability for detailed cosmic-ray composition analysis.

Abstract

The Calorimetric Electron Telescope (CALET), in operation on the International Space Station since 2015, collected a large sample of cosmic-ray iron over a wide energy interval. In this Letter a measurement of the iron spectrum is presented in the range of kinetic energy per nucleon from 10 GeV$/n$ to 2.0 TeV$/n$ allowing the inclusion of iron in the list of elements studied with unprecedented precision by space-borne instruments. The measurement is based on observations carried out from January 2016 to May 2020. The CALET instrument can identify individual nuclear species via a measurement of their electric charge with a dynamic range extending far beyond iron (up to atomic number $Z$ = 40). The energy is measured by a homogeneous calorimeter with a total equivalent thickness of 1.2 proton interaction lengths preceded by a thin (3 radiation lengths) imaging section providing tracking and energy sampling. The analysis of the data and the detailed assessment of systematic uncertainties are described and results are compared with the findings of previous experiments. The observed differential spectrum is consistent within the errors with previous experiments. In the region from 50 GeV$/n$ to 2 TeV$/n$ our present data are compatible with a single power law with spectral index -2.60 $\pm$ 0.03.