Published December 31, 2014
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Depth of maximum of air-shower profiles at the Pierre Auger Observatory. II. Composition implications

Creators

  • 1. Folkwang University of the Arts
  • 2. Instituto Superior Técnico
  • 3. Istituto Nazionale di Fisica Nucleare
  • 4. United States Department of Energy
  • 5. Centre national de la recherche scientifique
  • 6. University of São Paulo
  • 7. National Scientific and Technical Research Council
  • 8. New York University
  • 9. Ohio State University
  • 10. National Autonomous University of Mexico
  • 11. University of Santiago de Compostela
  • 12. University of Hamburg
  • 13. Radboud University Nijmegen
  • 14. City University of New York
  • 15. Complutense University of Madrid
  • 16. University of Bucharest
  • 17. University of Adelaide
  • 18. Karlsruhe Institute of Technology
  • 19. Max Planck Society
  • 20. Academy of Sciences of the Czech Republic
  • 21. Rio de Janeiro State University
  • 22. Polish Academy of Sciences
  • 23. Colorado State University
  • 24. University of Granada
  • 25. Instituto Politécnico Nacional
  • 26. Universidad Michoacana de San Nicolás de Hidalgo
  • 27. State University of Campinas
  • 28. Pennsylvania State University
  • 29. Case Western Reserve University
  • 30. University of Chicago
  • 31. University of Buenos Aires
  • 32. Federal Fluminense University
  • 33. University of Alcalá
  • 34. Michigan Technological University
  • 35. University of Groningen
  • 36. National University of La Plata
  • 37. RWTH Aachen University
  • 38. University of Nova Gorica
  • 39. University of Hawaii
  • 40. State University of Feira de Santana
  • 41. Palacký University, Olomouc
  • 42. University of New Mexico
  • 43. Universidade Federal do ABC
  • 44. Benemérita Universidad Autónoma de Puebla
  • 45. University of Leeds
  • 46. Louisiana State University System
  • 47. Louisiana State University
  • 48. Colorado School of Mines
  • 49. National University of Rosario
  • 50. Charles University in Prague
  • 51. Federal University of Bahia
  • 52. University of Nebraska–Lincoln
  • 53. INAF
  • 54. Northeastern University

Description

Using the data taken at the Pierre Auger Observatory between December 2004 and December 2012, we have examined the implications of the distributions of depths of atmospheric shower maximum (X-max), using a hybrid technique, for composition and hadronic interaction models. We do this by fitting the distributions with predictions from a variety of hadronic interaction models for variations in the composition of the primary cosmic rays and examining the quality of the fit. Regardless of what interaction model is assumed, we find that our data are not well described by a mix of protons and iron nuclei over most of the energy range. Acceptable fits can be obtained when intermediate masses are included, and when this is done consistent results for the proton and iron-nuclei contributions can be found using the available models. We observe a strong energy dependence of the resulting proton fractions, and find no support from any of the models for a significant contribution from iron nuclei. However, we also observe a significant disagreement between the models with respect to the relative contributions of the intermediate components.
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