Indications of Proton-Dominated Cosmic-Ray Composition above 1.6 EeV
R. U. AbbasiDepartment of Physics, University of Utah, Salt Lake City, Utah, USAT. Abu‐ZayyadDepartment of Physics, University of Utah, Salt Lake City, Utah, USAM. Al-SeadyDepartment of Physics, University of Utah, Salt Lake City, Utah, USAM. AllenDepartment of Physics, University of Utah, Salt Lake City, Utah, USAJ. F. AmmanLos Alamos National Laboratory, Los Alamos, New Mexico, USAR. J. AndersonDepartment of Physics, University of Utah, Salt Lake City, Utah, USAG. ArchboldDepartment of Physics, University of Utah, Salt Lake City, Utah, USAK. BelovDepartment of Physics, University of Utah, Salt Lake City, Utah, USAJ. W. BelzDepartment of Physics, University of Utah, Salt Lake City, Utah, USAD. R. BergmanDepartment of Physics and Astronomy, Rutgers University — The State University of New Jersey, Piscataway, New Jersey, USAS. A. BlakeDepartment of Physics, University of Utah, Salt Lake City, Utah, USAO. BrusovaDepartment of Physics, University of Utah, Salt Lake City, Utah, USAG. W. BurtDepartment of Physics, University of Utah, Salt Lake City, Utah, USAC. CannonDepartment of Physics, University of Utah, Salt Lake City, Utah, USAZ. CaoDepartment of Physics, University of Utah, Salt Lake City, Utah, USAW. DengDepartment of Physics, University of Utah, Salt Lake City, Utah, USAY. FedorovaDepartment of Physics, University of Utah, Salt Lake City, Utah, USAC. FinleyDepartment of Physics and Nevis Laboratory, Columbia University, New York, New York, USAR. GrayDepartment of Physics, University of Utah, Salt Lake City, Utah, USAW. HanlonDepartment of Physics, University of Utah, Salt Lake City, Utah, USAC. M. HoffmanLos Alamos National Laboratory, Los Alamos, New Mexico, USAM. H. HolzscheiterLos Alamos National Laboratory, Los Alamos, New Mexico, USAGareth HughesDepartment of Physics and Astronomy, Rutgers University — The State University of New Jersey, Piscataway, New Jersey, USAP. HüntemeyerDepartment of Physics, University of Utah, Salt Lake City, Utah, USAD. IvanovDepartment of Physics and Astronomy, Rutgers University — The State University of New Jersey, Piscataway, New Jersey, USAB. F. JonesDepartment of Physics, University of Utah, Salt Lake City, Utah, USAC. C. H. JuiDepartment of Physics, University of Utah, Salt Lake City, Utah, USAK. KimDepartment of Physics, University of Utah, Salt Lake City, Utah, USAM. A. KirnDepartment of Physics, Montana State University, Bozeman, Montana , USAE. C. LohDepartment of Physics, University of Utah, Salt Lake City, Utah, USAJ. LiuInstitute of High-Energy Physics, Beijing, ChinaJon Paul LundquistDepartment of Physics, University of Utah, Salt Lake City, Utah, USAM. M. MaestasDepartment of Physics, University of Utah, Salt Lake City, Utah, USANaohiro ManagoInstitute for Cosmic-Ray Research, University of Tokyo, Kashiwa, JapanLukáš MarekLos Alamos National Laboratory, Los Alamos, New Mexico, USAK. MartensDepartment of Physics, University of Utah, Salt Lake City, Utah, USAJohn MatthewsDepartment of Physics and Astronomy, University of New Mexico, Albuquerque, New Mexico, USAJ. N. MatthewsDepartment of Physics and Astronomy, University of New Mexico, Albuquerque, New Mexico, USASheva MooreDepartment of Physics, University of Utah, Salt Lake City, Utah, USAA. O’NeillDepartment of Physics and Nevis Laboratory, Columbia University, New York, New York, USAC. A. PainterLos Alamos National Laboratory, Los Alamos, New Mexico, USAL. PereraDepartment of Physics and Astronomy, Rutgers University — The State University of New Jersey, Piscataway, New Jersey, USAK. ReilDepartment of Physics, University of Utah, Salt Lake City, Utah, USAR. RiehleDepartment of Physics, University of Utah, Salt Lake City, Utah, USAM. S. RobertsDepartment of Physics and Astronomy, University of New Mexico, Albuquerque, New Mexico, USAD. RodriguezDepartment of Physics, University of Utah, Salt Lake City, Utah, USAM. SasakiInstitute for Cosmic-Ray Research, University of Tokyo, Kashiwa, JapanS. SchnetzerDepartment of Physics and Astronomy, Rutgers University — The State University of New Jersey, Piscataway, New Jersey, USAL. M. ScottDepartment of Physics and Astronomy, Rutgers University — The State University of New Jersey, Piscataway, New Jersey, USAG. SinnisLos Alamos National Laboratory, Los Alamos, New Mexico, USAJ. D. SmithDepartment of Physics, University of Utah, Salt Lake City, Utah, USAP. SokolskyDepartment of Physics, University of Utah, Salt Lake City, Utah, USAC. SongDepartment of Physics and Nevis Laboratory, Columbia University, New York, New York, USAR. W. SpringerDepartment of Physics, University of Utah, Salt Lake City, Utah, USAB. T. StokesDepartment of Physics, University of Utah, Salt Lake City, Utah, USASabrina A. StrattonDepartment of Physics and Astronomy, Rutgers University — The State University of New Jersey, Piscataway, New Jersey, USAS. B. ThomasDepartment of Physics, University of Utah, Salt Lake City, Utah, USAJ. R. ThomasDepartment of Physics, University of Utah, Salt Lake City, Utah, USAG. B. ThomsonDepartment of Physics and Astronomy, Rutgers University — The State University of New Jersey, Piscataway, New Jersey, USAD. TupaLos Alamos National Laboratory, Los Alamos, New Mexico, USAA. ZechDepartment of Physics and Astronomy, Rutgers University — The State University of New Jersey, Piscataway, New Jersey, USAX. ZhangDepartment of Physics and Nevis Laboratory, Columbia University, New York, New York, USA
2010en
ABI
Аннотация
We report studies of ultrahigh-energy cosmic-ray composition via analysis of depth of air shower maximum (${X}_{\mathrm{max}}$), for air shower events collected by the High-Resolution Fly's Eye (HiRes) observatory. The HiRes data are consistent with a constant elongation rate $d⟨{X}_{\mathrm{max}}⟩/d[\mathrm{log}(E)]$ of $47.9\ifmmode\pm\else\textpm\fi{}6.0(\mathrm{stat})\ifmmode\pm\else\textpm\fi{}3.2(\mathrm{syst})\text{ }\text{ }\mathrm{g}/{\mathrm{cm}}^{2}/\mathrm{\text{decade}}$ for energies between 1.6 and 63 EeV, and are consistent with a predominantly protonic composition of cosmic rays when interpreted via the QGSJET01 and QGSJET-II high-energy hadronic interaction models. These measurements constrain models in which the galactic-to-extragalactic transition is the cause of the energy spectrum ankle at $4\ifmmode\times\else\texttimes\fi{}{10}^{18}\text{ }\text{ }\mathrm{eV}$.
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