Helium nuclei research advances our understanding of cosmic ray origin
and propagation

Date:
May 25, 2023
Source:
Waseda University
Summary:
The latest observations from Low Earth Orbit with the International
Space Station provide further evidence of spectral hardening and
softening of cosmic ray particles.


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FULL STORY ==========================================================================
The CALorimetric Electron Telescope (CALET), aboard the Kibo's Exposed
Facility (EF) of the International Space Station, has been on a mission
to measure the flux of cosmic ray particles since 2015. In a new study,
an international team of researchers report the results of a direct
measurement of the cosmic ray helium spectrum using the data collected by CALET. In contrast to the single power-law that was previously believed to exist, analysis of the flux data collected between 2015 and 2022 reveals
that the energy distribution of cosmic ray helium nuclei follows a Double Broken Power Law.

Much of our understanding of the Universe and its mysterious phenomena is
based on theoretical interpretations. In order to deepen the understanding
of distant objects and energetic phenomena, astronomers are looking at
cosmic rays, which are high-energy charged particles composed of protons, electrons, atomic nuclei, and other subatomic particles. Such studies
have revealed that cosmic rays contain all the elements known to us in
the periodic table, suggesting that these elements originate from stars
and high-energy events such as supernovae. Additionally, due to their
charged nature, the path of cosmic rays through space is influenced by
the magnetic fields of interstellar phenomena and objects.

Detailed observations of cosmic rays can, thus, not only shed light on the origins of these particles but also decode the existence of high-energy
objects and phenomena such as supernova remnants, pulsars, and even dark matter. In an effort to better observe high-energy radiations, Japan,
Italy, and USA collaboratively established the CALorimetric Electron
Telescope (CALET) on the International Space Station in 2015.

In 2018, observations of the cosmic ray proton spectrum from 50 GeV
to 10 TeV revealed that the particle flux of protons at high energies
was significantly higher than expected. These results deviated from the conventional cosmic ray acceleration and propagation models that assume a "single power-law distribution," wherein the number of particles decrease
with increasing energy.

Consequently, in a study published in 2022, the CALET team, including researchers from Waseda University, found cosmic ray protons in the energy range of 50 GeV to 60 TeV to follow a "Double Broken Power Law." This
law assumes that the number of high-energy particles initially increase
until 10 TeV (known as spectral hardening) and then decrease with an
increase in energy (known as spectral softening).

Extending these observations further, the team has now found similar
trends of spectral hardening and softening in the cosmic ray helium
spectrum captured over a broad range of energy, from 40 GeV to 250 TeV.

The study, published in the journal Physical Review Letters on 27 April,
2023, was led by Associate Professor Kazuyoshi Kobayashi from Waseda University, Japan, along with contributions from Professor Emeritus Shoji Torii, Principal Investigator of the CALET project, also affiliated with
Waseda University, and Research Assistant Paolo Brogi from the University
of Siena in Italy.

"CALET has successfully observed energy spectral structure of cosmic ray helium, especially spectral hardening starting from around 1.3 TeV, and
the tendency of softening starting from around 30 TeV," says Kobayashi.

These observations are based on data collected by CALET aboard the International Space Station (ISS) between 2015 to 2022. Representing
the largest energy range to date for cosmic helium nuclei particles,
these observations provide additional evidence for deviation of the
particle flux from the single power-law model. The researchers noticed
that deviation from the expected power-law distribution was more than
eight standard deviations away from the mean, indicating a very low
probability of this deviation occurring by chance.

Notably, the initial spectral hardening observed in this data suggests
that there may be unique sources or mechanisms that are responsible for accelerating and propagating the helium nuclei to high energies. The
discovery of these spectral features is also supported by recent
observations from the Dark Matter Particle Explorer, and questions our
current understanding of the origin and nature of cosmic rays.

"These results would significantly contribute to the understanding
of cosmic ray acceleration in the supernova remnant and propagation
mechanism," says Torii.

These findings undoubtedly enhance our understanding of the Universe. Even
as we prepare for manned missions to the Moon and Mars, the energy
distribution of cosmic ray particles can also provide further insight
into the radiation environment in space and its effects on astronauts.

* RELATED_TOPICS
o Space_&_Time
# Cosmic_Rays # Astronomy # Cosmology # Solar_Flare #
NASA # Astrophysics # Space_Telescopes # Space_Exploration
* RELATED_TERMS
o Compton_Gamma_Ray_Observatory o International_Space_Station
o Space_observatory o Mir o Space_exploration o Space_debris
o Subatomic_particle o Lunar_space_elevator

========================================================================== Story Source: Materials provided by Waseda_University. Note: Content
may be edited for style and length.


========================================================================== Journal Reference:
1. O. Adriani, Y. Akaike, K. Asano, Y. Asaoka, E. Berti, G. Bigongiari,
W. R. Binns, M. Bongi, P. Brogi, A. Bruno,
J. H. Buckley, N. Cannady, G. Castellini, C. Checchia,
M. L. Cherry, G.

Collazuol, G. A. de Nolfo, K. Ebisawa, A. W. Ficklin,
H.

Fuke, S. Gonzi, T. G. Guzik, T. Hams, K. Hibino, M. Ichimura,
K.

Ioka, W. Ishizaki, M. H. Israel, K. Kasahara, J. Kataoka, R.

Kataoka, Y. Katayose, C. Kato, N. Kawanaka, Y. Kawakubo,
K. Kobayashi, K.

Kohri, H. S. Krawczynski, J. F. Krizmanic,
P. Maestro, P. S. Marrocchesi, A. M. Messineo,
J. W. Mitchell, S. Miyake, A. A. Moiseev, M. Mori,
N. Mori, H. M. Motz, K.

Munakata, S. Nakahira, J. Nishimura, S. Okuno, J. F. Ormes,
S.

Ozawa, L. Pacini, P. Papini, B. F. Rauch,
S. B. Ricciarini, K. Sakai, T. Sakamoto, M. Sasaki,
Y. Shimizu, A. Shiomi, P. Spillantini, F. Stolzi, S. Sugita,
A. Sulaj, M. Takita, T. Tamura, T. Terasawa, S.

Torii, Y. Tsunesada, Y. Uchihori, E. Vannuccini, J. P. Wefel,
K.

Yamaoka, S. Yanagita, A. Yoshida, K. Yoshida,
W. V. Zober. Direct Measurement of the Cosmic-Ray Helium
Spectrum from 40 GeV to 250 TeV with the Calorimetric Electron
Telescope on the International Space Station.

Physical Review Letters, 2023; 130 (17) DOI: 10.1103/
PhysRevLett.130.171002 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2023/05/230525141326.htm

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