1. The 23-European Symposium and the 32 Russian cosmic ray conference 3-7 July Moscow 1 Possible composition of the primary particles at ultrahigh energies observed at the Yakutsk array

2. The 23-European Symposium and the 32 Russian cosmic ray conference 3-7 July Moscow 2 By L.G. Dedenko 1, A.V. Glushkov 2, G.F. Fedorova 1, S.P. Knurenko 2, A.K. Makarov 2, L.T. Makarov 2, M.I. Pravdin 2, T.M. Roganova 1, A.A. Saburov 2, I.Ye. Sleptzov 2 1. M.V. Lomonosov Moscow State University, Faculty of Physics and D.V. Skobeltsin Institute of Nuclear Physics, Moscow, 119992, Leninskie Gory, Russian Federation 2. Insitute of cosmic rays and aeronomy. Yakutsk, Russian Federation

3. The 23-European Symposium and the 32 Russian cosmic ray conference 3-7 July Moscow 3 Motivation Testing the overall CR spectrum formation scenarios

4. The 23-European Symposium and the 32 Russian cosmic ray conference 3-7 July Moscow 4 The “dip” scenario of the overall CR spectrum formation In the model of uniformly distributed extragalactic sources with a power law spectrum of generation, the proton flux must first decrease (a dip), then increase (a bump) and drop steeply (the GZK effect) [3, 4]. [3] Berezinsky V S and Grigorieva S I 1988 Astron. Astrophys. 199 1 [4] Berezinsky V S, Gazizov A Z, Grigorieva S I 2006 Phys. Rev. D 74 043005

5. The 23-European Symposium and the 32 Russian cosmic ray conference 3-7 July Moscow 5 The “ankle” scenario In the alternative “ankle” scenario [6] the extragalactic component dominates at energies above 10 19 eV. The CR composition in this scenario is considerably heavier at energies 10 18 − 10 19 eV [6] Wibig T and Wolfendale W 2005 J. Phys. G: Nucl. Part. Phys. 31 255

6. The 23-European Symposium and the 32 Russian cosmic ray conference 3-7 July Moscow 6 The scenario by Berezhko E G The peak of rather heavy composition is predicted at energies ~ 10 17 eV followed by a sharp decrease of atomic number A within of the energy interval 10 17 − 10 18 eV. It is regarded as a signature of the transition from galactic to extragalactic CR. The second peak of heavy elements in the atomic number distribution is predicted at energy ~ 10 19 eV. So a profound increase of heavy composition should be observed within the energy interval 10 18 − 10 19 eV [5]. [5] Berezhko E G 2009 Astrophys. J. 698 L138

7. The 23-European Symposium and the 32 Russian cosmic ray conference 3-7 July Moscow 7 Study of composition Standard approach: The depth X max of shower maximum vs. E

8. The 23-European Symposium and the 32 Russian cosmic ray conference 3-7 July Moscow 8 Before LHC

9. The 23-European Symposium and the 32 Russian cosmic ray conference 3-7 July Moscow 9 After LHC

10. The 23-European Symposium and the 32 Russian cosmic ray conference 3-7 July Moscow 10 23-d European cosmic ray symposium Conclusion by T. Pierog, KIT, Karlsruhe, Germany (03.07.2012) … light composition is excluded at high energies …

11. The 23-European Symposium and the 32 Russian cosmic ray conference 3-7 July Moscow 11 Question by Angela Olinte The UHECR in CERN Febrary 2012 do we have pure protons anywhere???

12. The 23-European Symposium and the 32 Russian cosmic ray conference 3-7 July Moscow 12 We believe the answer is Yes

13. The 23-European Symposium and the 32 Russian cosmic ray conference 3-7 July Moscow 13 Alternative approach THE FRACTION OF MUONS α at 600 m from the shower core: α=s μ (600)/s(600) s μ (600) – a signal in the underground detector s(600) – a signal in the surface detector

14. The 23-European Symposium and the 32 Russian cosmic ray conference 3-7 July Moscow 14 Yakutsk array The Yakutsk array includes the surface scintillation detectors (SD), detectors of the Vavilov-Cherenkov radiation, underground detectors of muons (UD) with suggested the threshold energy ~1 GeV. It was shown that the less energetic muons may hit the underground detectors.

15. The 23-European Symposium and the 32 Russian cosmic ray conference 3-7 July Moscow 15 Simulations Simulations of the individual shower development in the atmosphere have been carried out with the help of the code CORSIKA-6.616 [7] Heck D, Knapp J, Capdevielle J-N et al. 1998 CORSIKA: A Monte Carlo Code to Simulate Extensive Air Showers Report FZKA 6019 Forschungszentrum Karlsruhe

16. The 23-European Symposium and the 32 Russian cosmic ray conference 3-7 July Moscow 16 Simulations in terms of the models QGSJET2 [8] Ostapchenko S S 2006 Nucl. Phys. Rev. B (Proc. Suppl.) 151 143 and Gheisha 2002 [9] Fesefeldt H C 1985 GHEISHA program Technical report PITHA 85-02, III Physikalisches Institut, RWTH Aachen. Physikzentrum with the weight parameter ε=10 -8 (thinning).

17. The 23-European Symposium and the 32 Russian cosmic ray conference 3-7 July Moscow 17 Simulations The program GEANT4 [10] The GEANT4 Collab. Available from http://geant4.web.cern.ch/geant4/support/ gettingstarted.shtml has been used to estimate signals in the scintillation detectors from electrons, positrons, gammas and muons in each individual shower.

18. The 23-European Symposium and the 32 Russian cosmic ray conference 3-7 July Moscow 18 Study of the chemical composition Muon density with energies above 1 GeV for the primary protons with the energy E: ρ μ (600, >1 GeV)=a·E b Decay processes are decreasing for higher energies E. b<1

19. The 23-European Symposium and the 32 Russian cosmic ray conference 3-7 July Moscow 19 Study of the chemical composition Muon density for the primary nuclei with atomic number A ρ μ (600)=a · A c · E b c>0 (c=1-b) QGSJET2: b=0.895, c=0.105 For Fe: A 0.105 =1.53

20. The 23-European Symposium and the 32 Russian cosmic ray conference 3-7 July Moscow 20 Study of the chemical composition The signals are calibrated in the surface detectors s(600)=∆E s (600)/δE s (600) and in the underground detectors s μ (600)=∆E u (600)/δE u (600) ∆E s (600) and ∆E u (600) from the EAS particles δE s (600) and δE u (600) from the one vertical muon

21. The 23-European Symposium and the 32 Russian cosmic ray conference 3-7 July Moscow 21 Standard approach of energy estimation at the Yakutsk array s(600) – the signal at 600 m in the vertical EAS measured in VEM’s (VERTICAL EQUIVALENT MUON) is used to estimate the energy E of EAS.

22. The 23-European Symposium and the 32 Russian cosmic ray conference 3-7 July Moscow 22 Standard approach of energy estimation at the Yakutsk array DATA: 1. The CIC method to estimate s(600) from data for the inclined EAS. 2. The signal s(600) is calibrated with help of the Vavilov-Cherenkov radiation E=(4.6+-1.2) · 10 17 · s(600) 0.98, eV

23. The 23-European Symposium and the 32 Russian cosmic ray conference 3-7 July Moscow 23 Standard AGASA approach Like AGASA: 1. The CIC method to estimate s(600) from data for the inclined EAS. 2. Calculation s(600) for EAS with the energy E: E=(3+-0.2)∙10 17 ·s(600), eV

24. The 23-European Symposium and the 32 Russian cosmic ray conference 3-7 July Moscow 24 Spectrum Data: s(600)= E/((4.6+-1.2) · 10 17 ) Simulation: s(600)= E/((3.+-0.2)∙10 17 ) The simulated signal larger! The fraction α is less!

25. The 23-European Symposium and the 32 Russian cosmic ray conference 3-7 July Moscow 25 Spectrum Data: s(600)= E/((4.6+-1.2) · 10 17 ) Simulation: s(600)= E/((3.+-0.2)∙10 17 ) The simulated signal larger! The energy spectra are different for these approaches.

26. The 23-European Symposium and the 32 Russian cosmic ray conference 3-7 July Moscow 26 Question Is it possible to increase the signal s(600) more, to be able to decrease the fraction α?

27. The 23-European Symposium and the 32 Russian cosmic ray conference 3-7 July Moscow 27 points ─ Yakutsk data circles ─ Yakutsk (calculation like AGASA) stars ─ PAO

28. The 23-European Symposium and the 32 Russian cosmic ray conference 3-7 July Moscow 28 Answer In the formula E=a·10 17 ·s(600) The coefficient a should be less than 4.6 and higher than 3 (difference by a factor 1.53). The magnitude a=3 leads to the maximal signal s(600) and the minimal value of the muon fraction.

29. The 23-European Symposium and the 32 Russian cosmic ray conference 3-7 July Moscow 29 Results Results of calculations

30. The 23-European Symposium and the 32 Russian cosmic ray conference 3-7 July Moscow 30 The fraction α of muons in EAS calculated in terms of the QGSJET-II and Gheisha-2002d models for the primary protons (solid line) and the primary iron nuclei (dashed line) and observed at the YaA [11] (dots with error bars) versus the energy E.

31. The 23-European Symposium and the 32 Russian cosmic ray conference 3-7 July Moscow 31 Question Where are protons?

32. The 23-European Symposium and the 32 Russian cosmic ray conference 3-7 July Moscow 32 Another question Are the models used reliable?

33. The 23-European Symposium and the 32 Russian cosmic ray conference 3-7 July Moscow 33 At energies above 100 GeV QGSJET2? Kochanov A A, Sinegovskaya T S, Sinegovsky S I 2008 Astrop. Physics 30 219 Panov A D, Adams J H Jr, Ahn H S et al. 2007 Bull. Russ. Acad. Sci. Phys. 71 494

34. The 23-European Symposium and the 32 Russian cosmic ray conference 3-7 July Moscow 34 The energy spectrum of vertical muons

35. The 23-European Symposium and the 32 Russian cosmic ray conference 3-7 July Moscow 35 Ratio R1 of the observed intensities (Δ − [21], - [22], ● − [23], ■ − [24], ○ − [25], + − [26]) of the vertical muons to the calculated muon intensity in terms of the QGSJET-II model vs. an impulse p of muons (A.Kochanov).

36. The 23-European Symposium and the 32 Russian cosmic ray conference 3-7 July Moscow 36

37. The 23-European Symposium and the 32 Russian cosmic ray conference 3-7 July Moscow 37 Conclusion Difference is increasing with the energy E from 1.5 to 3 at E=10 7 GeV. We adopted the minimal value 1.5 (A. Kochanov)

38. The 23-European Symposium and the 32 Russian cosmic ray conference 3-7 July Moscow 38 Below 100 GeV GHEISHA? Maris I C, Engel R, Arrido X et al. 2009 arXiv: 0907.0409v1 [astro-ph.CO]

39. The 23-European Symposium and the 32 Russian cosmic ray conference 3-7 July Moscow 39 Ratio R 2 of muon densities calculated in terms of the FLUCA model to the intensty calculated with the Gheisha-2002d model vs. a distance r from a shower axis (R. Engel).

40. The 23-European Symposium and the 32 Russian cosmic ray conference 3-7 July Moscow 40 Conclusion GHEISHA gives the density of muons at 600 m from the shower core by a factor f 3 =1.1 less than the FLUKA (R. Engel)

41. The 23-European Symposium and the 32 Russian cosmic ray conference 3-7 July Moscow 41 Corrected results

42. The 23-European Symposium and the 32 Russian cosmic ray conference 3-7 July Moscow 42 The fraction α of muons corrected due to results of [19, 21-26, 27, 29].

43. The 23-European Symposium and the 32 Russian cosmic ray conference 3-7 July Moscow 43 Answer We hope that protons are observed

44. The 23-European Symposium and the 32 Russian cosmic ray conference 3-7 July Moscow 44 The dependence of the atomic number A on α lnA= ln(α / α p ) / 0.105 Here α is a measured value and α p is calculated for protons.

45. The 23-European Symposium and the 32 Russian cosmic ray conference 3-7 July Moscow 45 Dependence of the atomic number on the energy E for YaA

46. The 23-European Symposium and the 32 Russian cosmic ray conference 3-7 July Moscow 46 CONCLUSION We hope that protons are observed in the energy interval 3·10 18 – 10 19 eV The new scenarios of the cosmic ray spectrum formation should be developed

47. The 23-European Symposium and the 32 Russian cosmic ray conference 3-7 July Moscow 47 Conclusions are model dependent The Coulomb scattering of charged particle (electrons, positrons) and the p t distribution of hadrons (for muon scattering) should be taken into account precisely in calculations of the lateral spread of these particles.

48. The 23-European Symposium and the 32 Russian cosmic ray conference 3-7 July Moscow 48 Acknowledgements. Moscow authors thank G.T. Zatsepin LSS (grant 871.2012.2 ) for support. Authors from Yakutsk thank RFBR grant 11- 02-12193 ofim and by the state contract 16.518.11.7075 from the Department of science and education of Russian Federation. for support.

49. The 23-European Symposium and the 32 Russian cosmic ray conference 3-7 July Moscow 49 Thank you for attention

50. The 23-European Symposium and the 32 Russian cosmic ray conference 3-7 July Moscow 50 Dependence of the atomic number on the energy E for various experiments: ● − [12], ■ − [9], □ − [33], ▲− [32].