Results%20of%20AGASA%20Experiment%20__Energy%20spectrum%20

1
Results of AGASA Experiment__Energy spectrum
Chemical composition __
Kenji SHINOZAKI Max-Planck-Institut für
Physik(Werner-Heisenberg-Institut)Munich,
Germanyon behalf of AGASA Collaboration
The Highest Energy Cosmic Rays and Their
Sources 21 23 May, 2004 _at_INR Moscow
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Outline

• Physics motivation
• Activities at Akeno Observatory
• Energy determination spectrum
• Shower properties analysis
• Systematic error in energy estimation
• Comparison with other results (HiRes A1)
• Muon component chemical composition
• Gamma-ray shower properties
• Chemical composition gamma-ray flux limit
  estimation
• Summary outlook

3
Physics motivation

• Understanding nature origin of UHECRs (gt1019eV)
• Energy spectrum
• Arrival direction distribution
• Chemical composition
• Super GZK particlesincl. highest energy cosmic
  rays (gt1020eV)
• Bottom-up scenarios
• AGNs / GRBs / Galactic clusters etc. ? Hadronic
  primaries predicted
• Top-Down scenarios
• Topological defects
• Super heavy dark matter
• Z-burst? Gamma-ray nucleon 1ries predicted
• Source location still not identified,..but ..

pUHECR ?CMB ? N p(E0 5x1019eV)
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Arrival direction distribution (gt4x1019eV ?lt50º)

• Small scale anisotropy
• Event clustering (gt4x1019eV within 2.5º)
• 6 doublets (?) 1 triplet (?) observed
• Against expected 2.0 doublets (Pch lt0. 1)
• There must be 250 EHECR sources (185340)

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Space angle distribution of events
Log Egt19.0 3.4s
Log Egt19.6 4.4s

• Significant peak _at_ 0 degree
• implying presence of compact EHECR sources

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AGASA Collaborators

• Institute for Cosmic Ray Research, University of
  Tokyo (Kashiwa)
• Masaki Fukushima, Naoaki Hayashida, Hideyuki
  Ohoka, Satoko Osone, Makoto Sasaki, Masahiro
  Takeda, Reiko Torii
• Kinki University (Osaka)
• Michiyuki Chikawa
• University of Yamanashi (Kofu)
• Ken Honda, Norio Kawasumi, Itsuro Tsushima
• Saitama University (Saitama)
• Naoya Inoue
• Musashi Institute of Technology (Tokyo)
• Kenji Kadota
• Tokyo Institute of Technology (Tokyo)
• Fumio Kakimoto
• Nishina Memorial Fundation (Tokyo)
• Koichi Kamata
• Hirosaki University (Hirosaki)
• Setsuo Kawaguchi
• Osaka City University (Osaka)
• Saburo Kawakami

Japan

• RIKEN (Wako)
• Yoshiya Kawasaki, Naoto Sakaki,Hirohiko M.
  Shimizu
• Ehime University (Matsuyama)
• Satoko Mizobuchi, Hisashi Yoshi
• Fukuki University of Technology (Fukui)
• Motohiko Nagano
• Communication Research Laboratory (Tokyo)
• Masahiko Sasano
• National Institute of Radiological Sciences
  (Chiba)
• Yukio Uchihori
• Chiba University (Chiba)
• Nobuyuki Sakurai, Shigeru Yoshida
• Max-Planck-Institute for Physics (Munich)
• Kenji Shinozaki, Masahiro Teshima
• University of Chicago (Chicago)
• Tokonatsu Yamamoto

Federal Republic of Germany
United States of America
We are INTERCONTINETAL collaboration among 31
(all Japanese) scientists from 17 institutes in 3
nations
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Akeno Observatory
Yakutsk ?????
Sea of Okhotsk??????

• Inst. for Cosmic Ray Research, Univ. of Tokyo
• Akeno,Yamanashi Japan (100km west of Tokyo)
• Lat. 35º47N, Long. 138º30E Altitude 900m
• Atom. depth 920 g/cm2
• Ave. pressure 910hPa
• Temp. 10 30?

Pacific Ocean???
Vladivostok ???????
Akeno??
Tsukuba???
Tokyo??
Mt.Fuji???
Main Building
Muon detectorstation
Cosmic Ray Imaging System
Leadburger
TA Prototype
AUGER Water Tank
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AGASA (Akeno Giant Air Shower Array)

• Detector station
• 111 surface detectors
• Effective area 100km2
• Optical fibre cable connection to observatory
• 27 muon detectors
• Southern region 30km2 coverage
• Operation
• Feb. 1990Dec.19954 separate-array operation
• Dec. 1995Jan.2004 Unified operation

8km
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• Surface detector
• 5cm thick scintillator
• Hamamatsu 5 R1512 PMT
• Muon detectors (2.810m2south region)
• 1420 Proportional counters
• Shielded by 30cm Fe or 1m concrete
• Threshold energy 0.5GeVxsec?
• Triggered by accompanying surface detector

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(No Transcript)
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Shower front structure (empirical)

• Modified from Linsley formula
• Delay time behind shower planeTd(R)ns 2.6 (
  1 R/30m )1.5 ?(R) -0.5
• Shower front thicknessTs(R)ns 2.6 ( 1
  R/30m )1.5 ?(R) -0.3

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Lateral distribution (empirical)
sec?1.1 S(600)10,30m2

• Modified Linsley formula ?(R) C (R/RM) a
  (1R/RM) (?a) 1(R/1000)2 d
• C Normalisation constant, a1.2, d0.6
• RM Moliere unit _at_ Akeno (91.6m)
• ? (3.970.13) (1.790.62) (sec? 1)
• Fluctuation of observed particle number
• s?2 ? 0.25 ?2 ? ( sscin2 srest2
  sstat2)

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Energy estimating relationships

• Energy vs. S(600) for vertical showers
• Dai et al.s MC result by COSMOSQCDJET (1988)E0
  eV 2.031017 S0 (600)
• S(600) Attenuation curve
• Empirical relationship (equi-intensity cut
  method)
• S? (600)S0 (600) expX0 / ?1 (sec?1) X0
  / ?2 (sec?1)2
• X 0 Atmospheric depth _at_ AKeno (920 g/cm2)
• ? 1 500 g/cm2
• ? 2 594 g/cm2

21019eV11019eV
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Event reconstruction

• Centre of gravity in ?ch distribution ?a priori
  core location
• Arrival direction optimisation (fitting shower
  front structure)
• Core location estimation (fitting lateral
  distribution)
• Iterative recalculation of Steps 2 3
• S? (600)?S0 (600) translation
• Energy estimation by S0 (600) vs. E0 relation

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Event sample
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Event sample
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Event selection criteria (standard)

• Dataset February 1990 January 2004
• Energy 1017eV (1018.5eV for spectrum)
• Zenith angle 45
• Core location inside AGASA boundary
• Number of hit detector 6
• Good reconstruction ?2 5 for arrival direction
  fitting
• ?2 1.5 for core location fitting

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Core location distribution (gt1018.5eV)Before
after unification
95.1204.01
90.295.12
Aperture 110km2sr extended to
160 km2sr
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Exposure (up to May 2003)

• AGASA Exposure
• 5.4x1016 m2 sec sr above 1019eV within ?lt45º
• AGASA has higher exposure than HiRes below
  3x1019eV

AGASA detector
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Reconstruction accuracy (Energy resolution,
Angular resolution)
8
20
6
15
Open angle ??º
4
Counts /bin
10
90
5
2
68
0
0
18 19 20

1.0 0.0 1.0 0.0 1.0
?Log(EnergyeV)
Log(EnergyeV)

• Energy resolution
• ?E0/E030 _at_1019.5eV
• ?E0/E025 _at_1020eV

• Angular resolution
• ??2.0º _at_1019.5eV
• ??1.3º _at_1020eV

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Energy spectrum (?lt45º)

• Super GZK-particles exist
• 11events above 1020eV
• Expected 1.9 event on GZK assumption for uniform
  sources

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Detector calibration
t1Peak
Pulse width distri. (10hr)
Gain variation (11yr)
a Slope
Linearity variation (11yr)
Channel 0.5ns

• PWD monitored every RUN (10h)
• Information taken into account in analysis
• Stability of detector
• Gain variation (peak of PWD) 0.7
• Linearity variation (slope of PWD) 1.6

Cf. ?t/lttgt?a/ltagt
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Detector simulation (GEANT)

• Detector container (0.4mm iron roof)
• Detector box (1.6mm iron)
• Scintillator (5cm thick)
• Earth (backscattering)

Detector response understood at 5 accuracy
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Energy conversion
AIRES QGSJET98 / SIBYLL for p Fe
Energy dispersion in atmosphere
90

• 90 primary energy carried by EM component
• primary particle model a few dependence
• S(600) depending less on primary particle / model

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Energy conversion factor
E0 a 1017eVx S(600) b
Ref. Model 1ry a b
Dai et al. 88 COSMOS QCDJET p 2.03 1.02
Singleelectron (900m)
Nagano et al. 99 (CORSIKA5.621) QGSJET98 p 2.07 1.03
Single PH peak (900m) Fe 2.34 1.00
SIBYLL1.6 p 2.30 1.03
Fe 2.19 1.03
Sakaki et al. 01 (AIRES2.2.1) QGSJET98 p 2.17 1.01
Single PW peak (667m) Fe 2.15 1.03
SIBYLL1.6 p 2.34 1.04
Fe 2.24 1.02

• Presently assigned primary energy 10 1 2
• Most conservative (We need to push up current
  energy)

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S(600) attenuation curve
AIRES code QGSJET / SIBYLL model for p / Fe
45º
45º
20.0
19.5
19.0
18.5
18.0

• S(600) attenuating rather slowly
• Correction factor less than 2 up to 45º zenith
  angle
• S(600) attenuation curve consistent between data
  MC
• Depending less on 1ry particles or interaction
  models
• Error on energy estimation 5

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Shower phenomenology effects(shower front
thickness/ delaying particles)
Particle arrival time distri. _at_2km (2x1020eV)
Shower front thickness

• Overestimation effects
• Important far away from core
• Data between several 100m 1kmdominant in
  energy estimation
• Effect of shower front thickness5 5
• Effect of delaying particles5 5

Delaying particles
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Major systematics in AGASA energy
Detector Detector Detector Detector Detector Detector
Absolute gain 0.7
Linearity 7
Detector response (container, box backscattering) 5
Energy estimator S(600) Energy estimator S(600) Energy estimator S(600) Energy estimator S(600) Energy estimator S(600) Energy estimator S(600)
Interaction model, primary particles, altitude Interaction model, primary particles, altitude 10 10 12
Shower Phenomenology Shower Phenomenology Shower Phenomenology Shower Phenomenology Shower Phenomenology Shower Phenomenology
Lateral distribution Lateral distribution 7
S(600) attenuation S(600) attenuation 5
Shower front structure Shower front structure 5 5 5
Late arriving particles Late arriving particles 5 5 5
Total Total Total Total 18
Systematics is energy independent above 1019eV
Feature of spectrum can hardly change that
extends beyond GZK cutoff.
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Consistency check in different aperture
Inside array Well inside array (2/3 AGASA)

• No systematic found in different apertures
• EHECR spectrum extension beyond GZK cut-off

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Recent spectra (AGASA vs. HiRes_at_Tsukuba ICRC)
HiRes Bergman et al. 03
vs. HiRes-II
vs. HiRes-I

• 2.5 sigma discrepancy between AGASA HiRes
• Energy scale difference by 25

vs. HiRes-stereo
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Comparison of Ne vs. S(600) in Akeno 1km2 array

• E0 eV 3.91015(Ne/106) 0.9
• Derived from attenuation curve comparison with
  Chacalaya (5200m 540g/cm2) experiment

• E0 8.51018 eV
• by Ne 5.13109
• E0 9.31018 eV
• by S(600) 45.7 /m2

Fairly good agreement between experiment MC
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AGASA vs. A1 comparison
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Chemical composition study

• Presence of Super-GZK particles
• No location identified as their sources
• Possibilities of Top-down models (TDs, Z-burst,
  SHDM)

UHECR composition is key discriminator of models
? Muons in giant air shower are key observable
for AGASA
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Gamma-ray shower properties

• Fewer muon content (photoproduced muon)
• Landau-Pomeranchuk-Migdal (LPM) effect
  (gt3x1019eV)
• Slowing down shower development
• Interaction in geomagnetic field (gtseveral x
  1019eV)
• Accelerating shower development
• LPM effect extinction
• Incident direction dependence

Simulated with MC by Stanev Vankov
1020eV Proton
1020eV Gamma-ray (LPM effect)
1020eV Gamma-ray (geomag. Interacted)
2000 g/cm2
0 g/cm2
500 g/cm2
1000 g/cm2
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Average S(600) vs. energy relationship for
gamma-rays (Akeno)

• Gamma-rayenergy underestimation
• 30 _at_1019 eV
• 50 _at_1019.5 eV(Maximum LPM effct)
• 30 _at_1020 eV(Recovered by geomag. effect)

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Lateral distribution of muons
No significant change in shape of LDM up to 1020eV
rm(R)C(R/R0)-1.2(1R/R0)-2.52(1(Rm/800)3)-0.
6 ,E01017.51019eV R0 Characteristic
distance (280m _at_q25o) Lateral distribution
function obtained by A1 Experiment (Hayashida et
al. 1995)
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Primary mass estimator
E01.8x1020eV rm(1000)2.4/m2
Lateral distribution

• Muon density at 1000mrm(1000)
• Fitting muon data in R800-1600m to LDM
• Error40

SAMPLE
Muon
Empirical formulae
Charged particle

• Muon density_at_1000m rµ (1000)
• 20 to total charged particles
• Feasible mass estimator for UHECRs

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Analysis

• Dataset (13 December 1995 31 December 2002)
• E01019eV
• Zenith angle q36º
• Normal event quality cuts
• 2 muon detectors in R800m1600m ? rm(1000)
• Statistics 129 events above 1019eV 19
  events above 1019.5eV

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Simulations

• Proton / iron primaries (AIRES2.2.1QGSJET98)
• Gamma-ray primaries (Geomag. AIRES LPM)
• Geomagnetic field effect
• Significant above 1019.5eV
• Code by Stanev Vankov
• LPM effect
• Significant above 1019.0eV
• Included in AIRES
• Detector configuration analysis process

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rm(1000) distribution (E0gt1019eV)
Consistent with proton dominant component
Average relationship rm (1000)m-2
(1.260.16)(E0eV/1019)0.930.13
1
0
Log(Muon density_at_1000mm2)
-1
-2
19
19.5
20
20.5
Log(Energy eV)
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Akeno 1km2 (A1) Hayashida et al. 95
(Interpretation by AIRESQGSJET)
Iron fraction(pFe 2comp. assumption)
A1 Preliminary
Present result (_at_90 CL)Fe frac. lt35 (1019
1019.5 eV) lt76 (above 1019.5eV)
A1 PRELIMINARY
Gradual decrease of Fe fraction between 1017.5
1019eV VERY PRELIMINARY
Haverah Park (HP) Ave et al. 03 Volcano Ranch
(VR) Dova et al. (present conf.) HiRes (HiRes)
Archbold et al. (present conf.)
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Limits on gamma-ray fraction
Assuming 2-comp. (pgamma-ray) primaries

• Gamma-ray fraction upper limits (_at_90CL)to
  observed events
• 34 (gt1019eV)(g/plt0.45)
• 56 (gt1019.5eV)(g/plt1.27)

Topological defects (Sigl et al. 01)
(Mx1016eV flux normalised_at_1020eV )
Z-burst model(Sigl et al. 01) (Flux
normalised_at_1020eV)
SHDM-model (Berezinski 03) (Mx1014eV flux
normalised_at_1020eV )
SHDM-model (Berezinski et al. 98) (Mx1014eV
flux normalised_at_1019eV )
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Summary

• AGASA operation
• 14year-observation watching 17km2 century sr
  exposure _at_ gt95 live-ratio
• Systematic errors in energy determination
• 18 independent of energy (1019eV)
• Super-GZK particles do exist
• 11 events observed gt1020eV against 1.9 on GZK
  assumption
• Energy spectrum remains extending beyond GZK
  cut-offConventional GZK mechanism can hardly
  explain!!
• Chemical composition
• Gradual lightening between 1017.5 1019eV
• Light component favoured _at_1019eV (AIRESQGSJET)
• Gamma-ray dominance negative at highest
  energiesFraction of gamma-rays lt56 _at_90CL (gt
  1019.5eV) (AIRESQGSJET)

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Another approach (Energy underestimation for
gamma-rays)

• Effects on UHE Gamma-ray
• LPM effect (gt3x1019eV)
• Geomagnetic effect (gt5x1019eV)
• Possible anisotropy in the sky expected for UHE
  gamma-rays
• No indication found for UHE gamma-rays
  (present low statistics)
• Possible approach for future large-scale
  experiments

Akeno sky up to 45o
This slide was shown for discussion_at_Rubtsovs
talk
q24.6
GMF
LPM