Title

Direct Measurement of the Cosmic-Ray Proton Spectrum from 50 GeV to 10 TeV with the Calorimetric Electron Telescope on the International Space Station

Authors

O. Adriani, Università degli Studi di Firenze
Y. Akaike, University of Maryland, Baltimore County (UMBC)
K. Asano, The University of Tokyo
Y. Asaoka, Waseda University
M. G. Bagliesi, Università degli Studi di Siena
E. Berti, Università degli Studi di Firenze
G. Bigongiari, Università degli Studi di Siena
W. R. Binns, Washington University in St. Louis, McDonnell Center for the Space Sciences
S. Bonechi, Università degli Studi di Siena
M. Bongi, Università degli Studi di Firenze
P. Brogi, Università degli Studi di Siena
A. Bruno, NASA Goddard Space Flight Center
J. H. Buckley, Washington University in St. Louis, McDonnell Center for the Space Sciences
N. Cannady, Louisiana State University
G. Castellini, Consiglio Nazionale delle Ricerche
C. Checchia, Università degli Studi di Padova
M. L. Cherry, Louisiana State University
G. Collazuol, Università degli Studi di Padova
V. Di Felice, Università degli Studi di Roma "Tor Vergata"
K. Ebisawa, JAXA Institute of Space and Astronautical Science
H. Fuke, JAXA Institute of Space and Astronautical Science
T. G. Guzik, Louisiana State University
T. Hams, University of Maryland, Baltimore County (UMBC)
N. Hasebe, Waseda University
K. Hibino, Kanagawa University
M. Ichimura, Hirosaki University
K. Ioka, Yukawa Institute for Theoretical Physics
W. Ishizaki, The University of Tokyo
M. H. Israel, Washington University in St. Louis, McDonnell Center for the Space Sciences
K. Kasahara, Waseda University
J. Kataoka, Waseda University
R. Kataoka, National Institute of Polar Research
Y. Katayose, Yokohama National University

Document Type

Article

Publication Date

5-10-2019

Abstract

In this paper, we present the analysis and results of a direct measurement of the cosmic-ray proton spectrum with the CALET instrument onboard the International Space Station, including the detailed assessment of systematic uncertainties. The observation period used in this analysis is from October 13, 2015 to August 31, 2018 (1054 days). We have achieved the very wide energy range necessary to carry out measurements of the spectrum from 50 GeV to 10 TeV covering, for the first time in space, with a single instrument the whole energy interval previously investigated in most cases in separate subranges by magnetic spectrometers (BESS-TeV, PAMELA, and AMS-02) and calorimetric instruments (ATIC, CREAM, and NUCLEON). The observed spectrum is consistent with AMS-02 but extends to nearly an order of magnitude higher energy, showing a very smooth transition of the power-law spectral index from-2.81±0.03 (50-500 GeV) neglecting solar modulation effects (or-2.87±0.06 including solar modulation effects in the lower energy region) to-2.56±0.04 (1-10 TeV), thereby confirming the existence of spectral hardening and providing evidence of a deviation from a single power law by more than 3σ.

Publication Source (Journal or Book title)

Physical Review Letters

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