1. Workshop on AstroParticle Physics, WAPP 2009 Bose Institute, Darjeeling, December 2009 Extensive Air Showers and Astroparticle Physics Observations and Interpretation through Simulations Suresh Tonwar Department of Physics, University of Maryland, College Park, MD 20742, USA

2. Extensive Air Showers and Astroparticle Physics Observations and Interpretation through Simulations Plan 1.Historical Remarks 2.Introduction to Primary Cosmic Rays 3.Development of Extensive air showers 4.Observable in Extensive Air Showers 5.Measurement of Observables 6.Interpretation of Observables 7.Results in AstroParticle Physics

3. EAS OBSERVABLES Electron lateral distribution Electron size Electron size spectrum Muon lateral distribution Muon mulyiplicity at a given distance from the shower axis Muon size Electron size – Muon size correlation Electron size – Muon multiplicity at a given distance from the shower axis

4. EAS OBSERVABLES Hadron energy spectrum Hadron energy flow Neutral to Charged ratio vs. Hadron energy Neutral to Charged ratio vs Electron size Cherenkov photon lateral distribution Cherenkov photon size Cherenkov photon pulse rise time N 2 Fluorescence Longitudinal development X max from Cherenkov or N 2 Fluorescence

5. Observation vs Simulation EAS observables at any observational level in the lower atmosphere, mountain altitude or sea level, are the result of an overlap of the products from thousands of interactions occurring at various levels in the atmosphere and their propagation upto the observational level. Most of these interaction processes are stochastic in nature and large fluctuations are quite common.

6. Observation vs Simulation As a result, the development of individual showers in the atmosphere is quite different even if the primary particle and primary energy are the same. Therefore, it is not possible to relate directly any observable with any physical variable of cosmic rays or particle interaction. It is necessary to calculate the expected characteristics of showers for various models of primary energy and composition and for various models of particle interactions over the broad energy range, from a few GeV to the highest primary energy capable of contributing to the observed showers.

7. EAS Simulation Inputs Primary energy spectrum and elemental composition Model of primary cosmic rays – energy spectrum and flux of various nuclear groups over a broad energy range, including changes in spectral index at specific energies. For example, showers of observable size 10 5.0 -10 5.2 at the Darjeeling level can be produced by protons of energy over the broad range, ~ 3x10 13 – 3x10 15 eV, or by N nuclei of ~ 4x10 13 – 4x10 15 eV or by Fe nuclei of ~9x10 13 – 9x10 15 eV. Primary all-particle energy spectrum shows a change in power-law spectral index from -2.6 to -3.1 around energy ~ 3x10 15. A similar change has to be assumed in the spectra of all the elements at energies which are determined by the assumed physics of the spectral change, for example, due to leakage from the galactic disk. EAS observables at any observational level in the lower atmosphere, mountain altitude or sea level, are the result of an overlap of the products from thousands of interactions occurring at various levels in the atmosphere and their propagation upto the observational level..

8. EAS Simulation Inputs Interaction characteristics and their energy dependence Proton-air inelastic collision cross-section and its variation over the energy range, 10 GeV to 10 11 GeV. Similarly cross- sections for inelastic collisions of various nuclei from He nuclei to Fe nuclei.

9. Inelastic Interaction Cross-Section for Protons with Air Nuclei

10. Inelastic Interaction Cross-Section for Various Nuclear Elements with Air Nuclei

11. Inelastic Interaction Cross-Section for Various Particles with Air Nuclei

12. Photo-Pion Production Cross-Section

13. Inelastic cross-Section and Fluctuations in the 1 st Point of Interaction In a simple case, we can assume, 80 gm/cm 2, 120 gm/cm 2 and 140 gm/cm 2 as the interaction mean free paths for protons-air, pion-air and kaon-air inelastic collisions respectively. Nearly 67% of primary protons interact within the top 80 gm/cm 2 of the atmosphere. About 25% protons skip the first 80 gm/cm 2 and the first interaction is between 80 gm/cm 2 and 160 gm/cm 2. Further ~ 7% protons skip the first 160 gm/cm 2 and interact between 160 gm/cm 2 and 240 g/cm 2.

14. Inelastic cross-Section and Fluctuations in the 1 st Point of Interaction Observations show that the attenuation mean free path for shower size around size ~ 10 6 particles is 160 gm/cm 2. Assuming the rest of the shower development remains the same, ~25% showers have ~ 50% larger shower size at the observational level of 800 gm/cm 2 (Darjeeling) and ~7% showers have size larger by more than a factor of 2. Therefore, in an average picture, showers which started later in the atmosphere get assigned a higher primary energy as their observed size is larger, causing an error in the determination of the size spectrum and flux measurements.

15. EAS Simulation Inputs Interaction characteristics and their energy dependence Inelasticity – fraction of energy lost by the primary particle in its interaction with the air nuclei Direct measurements on ‘inelasticity’ are available only from ‘Fixed-Target’ experiments at accelerators for protons only upto 450 GeV and much lower energies for other particles like pions and kaons. In collider experiments, particles travelling in the very forward direction (x f > 0.9) remain within the beam-pipes and go undetected and unmeasured.

16. EAS Simulation Inputs Longitudinal Momentum Distribution – Forward Region

17. EAS Simulation Inputs Longitudinal Momentum Distribution – Central Region

19. EAS Simulation Inputs Charged Particle Multiplicity – Central Region

20. EAS Simulation Inputs Multiplicity Probability Distribution – Central Region

21. EAS Simulation Inputs Particle Composition – Central Region

22. Model of the Atmosphere over the Observational Site and its Variation during the Seasons

23. Energy Loss for Muons in Air Ionization and Pair Production

24. Hadron Interaction Models in CORSIKA

25. EAS Simulation Results Shower Size (Ne) Distributions

26. EAS Simulation Results Muon Size (Nmu) Distributions

27. EAS Simulation Results Muon Size vs. Primary Energy

28. Observations vs. Simulations Muon Distributions (QGSJet) – GRAPES Experiment

29. Observations vs. Simulations Muon Distributions (SYBILL) – GRAPES Experiment

30. Observations vs. Simulations Spectral Break – GRAPES Experiment

31. Observations vs. Simulations Primary Proton Spectrum – GRAPES Experiment

32. Observations vs. Simulations Primary Helium Spectrum – GRAPES Experiment

33. Observations vs. Simulations All Particle Spectrum – GRAPES Experiment

34. Spectrum at the Highest Energies Results from the Pierre Auger Observatory

35. Observations vs. Simulations Shower Maximum vs. Primary Energy

36. Cosmic Ray Cources at the Highest Energies Results from the Pierre Auger Observatory

37. WAPP 2009 Darjeeling, December 2009 Thanks for your kind attention Special Thanks to the Organizers for their kind hospitality and excellent organizational arrangements Wishing you all Merry Christmas and a Joyful and Productive New Year 2010