Neutrons and antiprotons in ultrahigh-energy cosmic rays

  • W. -Y. P. Hwang
  • Bo-Qiang MaEmail author
Original Article


The neutron fraction in the very high-energy cosmic rays near the Greisen-Zatsepin-Kuzmin (GZK) cutoff energy is analyzed by taking into account the time dilation effect of the neutron decays and also the pion photoproduction behaviors above the GZK cutoff. We predict a non-trivial neutron fraction above the GZK cutoff and a negligibly small neutron fraction below. However, there should be a large antiproton fraction in the high-energy cosmic rays below the GZK cutoff in several existing models for the observed cosmic-ray events above and near the GZK cutoff. Such a large antiproton fraction can manifest itself by the muon charge ratio μ+- in the collisions of the primary nucleon cosmic rays with the atmosphere, if there is no neutron contribution. We suggest to use the muon charge ratio as one of the information to detect the composition of the primary cosmic rays near or below the GZK cutoff.


98.70.Sa Cosmic rays (including sources, origin, acceleration, and interactions) 03.30.+p Special relativity 13.85.Tp Cosmic-ray interactions 98.70.Vc Background radiations 


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  1. 1.
    For a few excellent reviews, see, e.g., F. Halzen, Int. J. Mod. Phys. A 17, 3432 (2002)Google Scholar
  2. 2.
    K. Greisen, Phys. Rev. Lett. 16, 748 (1966)Google Scholar
  3. 3.
    F.W. Stecker, Phys. Rev. Lett. 21, 1016 (1968). For an extensive review with recent progress, see F.W. Stecker, astro-ph/0101072.Google Scholar
  4. 4.
    T. Weiler, Phys. Rev. Lett. 49, 234 (1982)Google Scholar
  5. 5.
    D. Fargion, B. Mele, A. Salis, Astrophys. J. 517, 725 (1999).Google Scholar
  6. 6.
    G. Gelmini, A. Kusenko, Phys. Rev. Lett. 82, 5202 (1999)Google Scholar
  7. 7.
    V. Berezinsky, M. Kachelrie, A. Vilenkin, Phys. Rev. Lett. 79, 4302 (1997)Google Scholar
  8. 8.
    For a review, see, e.g., P. Bhattacharjee, G. Sigl, Phys. Rep. 327, 110 (2000).Google Scholar
  9. 9.
    G.F. Chew, M.L. Goldberger, F.E. Low, Y. Nambu, Phys. Rev. 106, 1345 (1957)Google Scholar
  10. 10.
    Z. Li, Phys. Rev. D 50, 5639 (1994).Google Scholar
  11. 11.
    T. Fujii , Phys. Rev. Lett. 28, 1672 (1972)Google Scholar
  12. 12.
    W.Y.P. Hwang, T.S.H. Lee, B.-Q. Ma, Nucl. Phys. A 737, 294 (2004).Google Scholar
  13. 13.
    For a review, see, e.g., J.P. Wefel, J. Phys. G 29, 821 (2003).Google Scholar
  14. 14.
    R.K. Adair, Phys. Rev. Lett. 33, 115 (1974)Google Scholar
  15. 15.
    M.G. Thompson, M.R. Whalley, J. Phys. G 3, 97 (1977)Google Scholar
  16. 16.
    See, e.g., B.-Q. Ma, I. Schmidt, J. Soffer, J.-J. Yang, Nucl. Phys. A 703, 346 (2002).Google Scholar
  17. 17.
    See, e.g., B.-Q. Ma, I. Schmidt, J.-J. Yang, Phys. Rev. D 65, 034010 (2002).Google Scholar
  18. 18.
    Y.-J. Zhang, B. Zhang, B.-Q. Ma, Phys. Lett. B 523, 260 (2001).Google Scholar
  19. 19.
    J.N. Capdevielle, Y. Muraki, Astropart. Phys. 11, 335 (1999). See, e.g., fig. 7.Google Scholar
  20. 20.
    F.W. Stecker, Phys. Rev. Lett. 80, 1816 (1998)Google Scholar
  21. 21.
    See, e.g., K. Rawlins, 2001 PhD Thesis at UW-Madison.Google Scholar
  22. 22.
    N. Nayashida , J. Phys. G 21, 1101 (1995).Google Scholar
  23. 23.
    K.-H. Kampert, astro-ph/0204205Google Scholar
  24. 24.
    J. Kremer , Phys. Rev. Lett. 83, 4241 (1999).Google Scholar
  25. 25.
    A.A. Mikhailov, J. Phys. G 20, 841 (1994)Google Scholar

Copyright information

© Società Italiana di Fisica and Springer-Verlag 2005

Authors and Affiliations

  1. 1.Department of PhysicsNational Taiwan UniversityTaipeiTaiwan
  2. 2.Department of PhysicsPeking UniversityBeijing

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