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.

O Adriani,K Yamaoka,S Sugita,A Bruno,H Fuke,M Bongi,T Tamura,T Terasawa,T Hams,S Nakahira,P Brogi,J Kataoka,S Yanagita,Y Tsunesada,T Sakamoto,K Kasahara,Y Kawakubo,Y Uchihori,G Bigongiari,M Ichimura,S Gonzi,A Sulaj,N Cannady,G Collazuol,Y Asaoka,N Ospina,M Takita,N Mori,E Vannuccini,K Munakata,C Checchia,S Okuno,K Hibino,A Shiomi,G Castellini,P Papini,P Maestro,S Ozawa,A Yoshida,W Ishizaki,Y Katayose,C Kato,M Mori,G A De Nolfo ,J T Link ,Ryuho Kataoka ,M H Israel ,А А Моисеев ,M L Cherry ,Yuki Shimizu ,Misao Sasaki ,E Berti ,Kazuyoshi Kobayashi ,Shoko Miyake ,H Motz ,J F Ormes ,W R Binns ,Kunihito Ioka ,T G Guzik ,Yosui Akaike ,Kazunori Kohri ,Francesco Stolzi ,S Ricciarini ,Shoji Torii ,Jun Nishimura ,H Krawczynski ,J H Buckley ,Kentaro Asano ,J W Mitchell ,П Спиллантини ,A Messineo ,B F Rauch ,P S Marrocchesi ,Norita Kawanaka ,Ken Ebisawa ,J P Wefel ,John F Krizmanic ,Kazuhiro Sakai ,Lorenzo Pacini ,Kenji Yoshida

doi:10.1103/physrevlett.126.241101

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 (3radiation 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±0.03.

Highlights

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
In order to discriminate among different interpretations, a precision measurement of the iron spectrum is of particular interest as iron provides favorable conditions for observations, because of its largest relative abundance among the heavy elements, and for a negligible contamination from spallation of higher mass elements

Summary

Published by the American Physical Society

CALET is a space-based instrument [35,36,37] optimized for the measurement of the all-electron spectrum [38,39], and designed to study individual chemical elements in CRs from proton to iron and above, exploring particle energies up to the PeV scale. This can be achieved thanks to its large dynamic range, adequate calorimetric depth, accurate tracking, and excellent charge identification capabilities. A linear interpolation is used to determine the correction factor for intermediate energies

Number of Events

Systematic uncertainties

Findings

Spectral Index