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AGASA Results

AGASA Results. Masahiro Teshima Max-Planck-Institut f ü r Physik, M ü nchen, Germany for AGASA collaboration. Cosmic Ray Energy Spectrum. GZK mechanism. Ｎ. P. Δ. Super GZK part. ~1/km 2 century. π. γ3K. AGASA Energy Spectrum. AGASA Akeno Giant Air Shower Array. 0 4km.

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AGASA Results

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  1. AGASA Results Masahiro Teshima Max-Planck-Institut für Physik, München, Germany for AGASA collaboration

  2. Cosmic Ray Energy Spectrum GZK mechanism Ｎ P Δ Super GZK part. ~1/km2 century π γ3K AGASA Energy Spectrum

  3. AGASAAkeno Giant Air Shower Array 0 4km 111 Electron Det. 27 Muon Det.

  4. Exposures of various experiments Auger

  5. Detector Calibration in AGASA experiment Detector Position Gain as a function of time (11years data) Survey from Airplane ΔＸ，ΔＹ＝0.1m, ΔＺ＝0.3m Cable delay (optic fiber cable) Accuracy of 100ps by measuring the round trip time in each run Linearity as a function of time (11years data) Detector Gain by muons in each run

  6. Linearity check after dismantling detectors in 2004 Feb At Akeno Observatory Central building in 2004 Jan

  7. Detector Response vertical θ = 60deg Detector Housing (Fe 0.4mm) Detector Box (Fe 1.6mm) Scintillator (50mm) Earth (Backscattering) Detector Simulation (GEANT) Energy spectra of shower particles

  8. EnergyDetermination • Local density at 600m • Good energy estimator by M.Hillas E=2.13x1020eV

  9. The Highest Energy Event 2.5 x1020eV on 10 May 2001

  10. Attenuation curve S(600) vs Nch 1018eV Proton Atmospheric depth

  11. S600 Attenuation curve 20.0 19.5 19.0 18.5 18.0 Atmospheric depth

  12. Proton S600 Intrinsic fluctuation Iron

  13. The Conversion from S600 to Energy Muon/Neutrino Ele. Mag

  14. Energy Resolution 25% 30% mainly due to measurement errors (particle density measurement and core location determination)not due to shower fluctuation

  15. Major Systematics in AGASAastro-ph/0209422 • Detector • Detector Absolute gain ± 0.7% • Detector Linearity ± 7% • Detector response(box, housing) ± 5% • Energy Estimator S(600) • Interaction model, P/Fe, Height ±15% • Air shower phenomenology • Lateral distribution function ± 7% • S(600) attenuation ± 5% • Shower front structure ± 5% • Delayed particle(neutron) ± 5% • Total± 18%

  16. Energy Spectrum by AGASA (θ<45) 11 obs. / 1.8 exp. 4.2σ 5.1 x 1016 m2 s sr

  17. The Energy spectrum by AGASA Red: well inside the array (Cut the event near the boundary of array)

  18. AGASA vs HiRes (astro-ph) See new paper: Energy determination in AGASA (astro-ph/0209422)

  19. Critical review for energy determination • Fitting the lateral distribution of shower particle density • Empirical formula (exclude errors in M.C. but limited by statistics) • no energy dependence • Linear dependence on sec(theta)  lateral distribution obtained by Corisika

  20. Lateral distribution Corskika lateral S(600) Empirical lateral S(600) Slope parameter eta

  21. S600 attenuation with recent Corsika We are very close to S600 maximum at 1020eV Overestimation factor if CORSIKA is right

  22. Preliminary spectra with recent Corsika Sec(theta) =1.0 - 1.2 Sec(theta) =1.2 - 1.4

  23. Comparison of original energy spectrum and new spectra based on Corsika ~10% ~15% Energy shift ~10% at 1019eV ~15% at 1020eV to lower direction Above 1020eV 11events  5~6 events Spectrum becomes more featureless

  24. Auger Energy Spectrumwith FD calibration AGASA Corsika by Arisaka

  25. Auger Energy Spectrumwith MC energy by Arisaka AGASA Corsika by Arisaka

  26. Arrival Direction Distribution >4x1019eVzenith angle <50deg. • Isotropic in large scale  Extra-Galactic • But, Clusters in small scale (Δθ<2.5deg) • 1triplet and 6 doublets (2.0 doublets are expected from random)

  27. Space Angle Distribution of Arbitrary two events >4x1019eV Normalized sigma by Li & Ma 3.2 sigma

  28. Arrival Direction Distribution >1019eV

  29. Space Angle Distribution Log E>19.0 Log E>19.2 Log E>19.4 Log E>19.6

  30. ρμ(1000) distribution

  31. Summary • Super GZK particles exist • Preliminary study with recent CORSIKA • If recent CORSIKA describes showers correctly, AGASA energy scale will shift down by ~10% at 1019eV and by ~15% at 1020eV on average • Spectrum seems to be more featureless (in preliminary study) ?? • Discrepancy between AGASA and HiRes becomes less significant • Small scale anisotropy of UHECR • The arrival direction of UHECRs is uniform in large scale • But AGASA data shows clusters, 1 triplets and 6 doublets  granularity • Source density ~10-5/Mpc3 ~ density of AGNs • Re-analysis is on-going with new shower front structure (but very slow) • Chemical composition at 1019eV • Consistent with light component (P) • No gamma ray dominance, γ/all <34%

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