MSGID: 1:317/3 647035fb   
   PID: hpt/lnx 1.9.0-cur 2019-01-08   
   TID: hpt/lnx 1.9.0-cur 2019-01-08   
    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   
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   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   
      
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   Story Source: Materials provided by Waseda_University. Note: Content   
   may be edited for style and length.   
      
      
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   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   
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   Link to news story:   
   https://www.sciencedaily.com/releases/2023/05/230525141326.htm   
      
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