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

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

AGASA Akeno Giant Air Shower Array 0 4km 111 Electron Det. 27 Muon Det.

Exposures of various experiments Auger

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

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

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

Energy Determination Local density at 600m Good energy estimator by M.Hillas E=2.13x1020eV

The Highest Energy Event 2.5 x1020eV on 10 May 2001

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

S600 Attenuation curve 20.0 19.5 19.0 18.5 18.0 Atmospheric depth

S600 Intrinsic fluctuation Proton S600 Intrinsic fluctuation Iron

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

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

Major Systematics in AGASA astro-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%

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

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

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

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

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

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

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

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

Auger Energy Spectrum with FD calibration AGASA Corsika by Arisaka

Auger Energy Spectrum with MC energy by Arisaka AGASA Corsika by Arisaka

Arrival Direction Distribution >4x1019eV zenith 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)

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

Arrival Direction Distribution >1019eV

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

ρμ(1000) distribution

Summary Super GZK particles exist Small scale anisotropy of UHECR 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%