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Suresh Tonwar Department of Physics, University of Maryland , College Park, MD 20742, USA

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.

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Suresh Tonwar Department of Physics, University of Maryland , College Park, MD 20742, USA

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

  2. Extensive Air Showers and Astroparticle PhysicsObservations and Interpretation through Simulations Plan Historical Remarks Introduction to Primary Cosmic Rays Development of Extensive air showers Observable in Extensive Air Showers Measurement of Observables Interpretation of Observables 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 • N2 Fluorescence • Longitudinal development • Xmax from Cherenkov or N2 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 InputsPrimary 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 105.0 -105.2 at the Darjeeling level can be produced by protons of energy over the broad range, ~ 3x1013 – 3x1015 eV, or by N nuclei of ~ 4x1013 – 4x1015 eV or by Fe nuclei of ~9x1013 – 9x1015 eV. • Primary all-particle energy spectrum shows a change in power-law spectral index from -2.6 to -3.1 around energy ~ 3x1015 . 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 InputsInteraction characteristics and their energy dependence • Proton-air inelastic collision cross-section and its variation over the energy range, 10 GeV to 1011 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 1st Point of Interaction • In a simple case, we can assume, 80 gm/cm2, 120 gm/cm2 and 140 gm/cm2 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/cm2 of the atmosphere. About 25% protons skip the first 80 gm/cm2 and the first interaction is between 80 gm/cm2 and 160 gm/cm2. • Further ~ 7% protons skip the first 160 gm/cm2 and interact between 160 gm/cm2 and 240 g/cm2.

  14. Inelastic cross-Section and Fluctuations in the 1st Point of Interaction • Observations show that the attenuation mean free path for shower size around size ~ 106 particles is 160 gm/cm2. • Assuming the rest of the shower development remains the same, ~25% showers have ~ 50% larger shower size at the observational level of 800 gm/cm2 (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 InputsInteraction 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 (xf > 0.9) remain within the beam-pipes and go undetected and unmeasured.

  16. EAS Simulation InputsLongitudinal Momentum Distribution – Forward Region

  17. EAS Simulation InputsLongitudinal Momentum Distribution – Central Region

  18. EAS Simulation InputsLongitudinal Momentum Distribution – Central Region

  19. EAS Simulation InputsCharged Particle Multiplicity – Central Region

  20. EAS Simulation InputsMultiplicity Probability Distribution – Central Region

  21. EAS Simulation InputsParticle 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 ResultsShower Size (Ne) Distributions

  26. EAS Simulation ResultsMuon Size (Nmu) Distributions

  27. EAS Simulation ResultsMuon Size vs. Primary Energy

  28. Observations vs. SimulationsMuon Distributions (QGSJet) – GRAPES Experiment

  29. Observations vs. SimulationsMuon Distributions (SYBILL) – GRAPES Experiment

  30. Observations vs. SimulationsSpectral Break – GRAPES Experiment

  31. Observations vs. SimulationsPrimary Proton Spectrum – GRAPES Experiment

  32. Observations vs. SimulationsPrimary Helium Spectrum – GRAPES Experiment

  33. Observations vs. SimulationsAll Particle Spectrum – GRAPES Experiment

  34. Spectrum at the Highest EnergiesResults from the Pierre Auger Observatory

  35. Observations vs. SimulationsShower Maximum vs. Primary Energy

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

  37. WAPP 2009Darjeeling, 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

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