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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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AGASA Results

Masahiro Teshima

Max-Planck-Institut für Physik, München, Germany

for AGASA collaboration

Cosmic Ray Energy Spectrum

GZK mechanism



Super GZK part.

~1/km2 century



AGASA Energy Spectrum

AGASAAkeno Giant Air Shower Array

0 4km

111 Electron Det.

27 Muon Det.

Exposures of various experiments


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




θ = 60deg

Detector Housing (Fe 0.4mm)

Detector Box (Fe 1.6mm)

Scintillator (50mm)

Earth (Backscattering)

Detector Simulation (GEANT)

Energy spectra of shower particles


  • Local density at 600m

    • Good energy estimator by M.Hillas


The Highest Energy Event

2.5 x1020eV on 10 May 2001

Attenuation curve

S(600) vs Nch

1018eV Proton

Atmospheric depth

S600 Attenuation curve






Atmospheric depth


S600 Intrinsic fluctuation


The Conversion

from S600 to Energy


Ele. Mag

Energy Resolution



mainly due to measurement errors (particle density measurement and core location determination)not due to shower fluctuation

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%

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

Corskika lateral S(600)

Empirical lateral S(600)

Slope parameter eta

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

Auger Energy Spectrumwith FD calibration



by Arisaka

Auger Energy Spectrumwith MC energy by Arisaka



by Arisaka

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)

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>19.0

Log E>19.2

Log E>19.4

Log E>19.6

ρμ(1000) distribution


  • 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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