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Results of Experiments in AkenoResults of Experiments in Akeno
Kenji SHINOZAKIKenji SHINOZAKI
Max-Planck-Institut fMax-Planck-Institut füür Physikr Physik (Werner-Heisenberg-Institut)(Werner-Heisenberg-Institut)Munich, GermanyMunich, Germany
on behalf of AGASA Collaboration
2nd International Workshop on Ultra-high-energy cosmic rays and their sources14 – 16 April, 2005 @INR Moscow
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• Institute for Cosmic Ray Research, University of Tokyo (Kashiwa)
– Masaki Fukushima, Naoaki Hayashida, Hideyuki Ohoka, Satoko Osone,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
• RIKEN (Wako)– Yoshiya Kawasaki, Hirohiko M. Shimizu Chiba Unive
rsity (Chiba) – Keiichi Mase, Nobuyuki Sakurai,
Shigeru Yoshida• Ehime University (Matsuyama)
– Satoko Mizobuchi, Hisashi Yoshi• Fukuki University of Technology (Fukui)
– Motohiko Nagano• Aoyama Gakuin University (Sagamihara)
– Naoto Sakaki• National Maritine Research Institute (Sagamihara)
– Masahiko Sasano• Max-Planck-Institute for Physics (Munich, GER)
– Kenji Shinozaki, Masahiro Teshima • National Institute of Radiological Sciences (Chiba)
– Yukio Uchihori • University of Chicago (Chicago, USA)
– Tokonatsu Yamamoto
AGASA Collaborators
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Physics motivation• Understanding nature & origin of UHECRs
(>1019eV)– Energy spectrum– Arrival direction distribution– Chemical composition
• Super GZK particlesincl. highest energy cosmic rays (>1020eV) – Bottom-up scenarios
• AGNs / GRBs / Collinding galactic 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,pUHECR γCMB → N π+
(E0 ~5x1019eV)
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Air shower development & observation techniques
• Surface array observation (eg. AGASA)– Sampling particles in shower front reaching ground
• Measurement of particle distribution (electron/muon)
• Fluorescence technique (eg. HiRes, EUSO)– Imaging fluorescence light emitted along air shower track
• Measurement of longitudinal development (Track length; Xmax)
• Hybrid measurement (eg. Auger, Telescope Array)
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Outline• Physics motivation & observation principle
• Activities at Akeno Observatory
• Energy determination & spectrum– Shower properties & analysis– Systematic error in energy estimation
• UHECR Anisotropy – 1018eV energies– 1019eV energy and Super-GZK
• Muon component & chemical composition
• Summary & outlook
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Pre-AGASA
AGASA
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AGASA era
AGASA
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AGASA (Akeno Giant Air Shower Array)• Detector station
– 111 surface detectors• Effective area ~100km2
• Optical fibre cable connection to observatory
• Triggered by 5-neighbouringhit detector within 25s
– 27 muon detectors• Southern region
~30km2 coverage • Operation
– Feb. 1990–Dec.19954 separate-array operation
– Dec. 1995–Jan.2004 Unified operation
SB
NB
AB
TB
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• Surface detector– 5cm thick plastic scintillator– Hamamatsu 5” R1512 PMT
• Muon detectors (2.8–10m2;south region)
– 14–20 Proportional counters– Shielded by 30cm Fe or 1m concrete
• Threshold energy: 0.5GeVxsecθ– Triggered by accompanying surface detector
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Event sample & observables
4.11x1019eV
• Energy estimator (charged particle density @600m): S(600)
E0 = 2.0 × 1017 S(600) for vertical showers → less dependent of 1ries or interaction models
• Primary mass estimator (muon density@1000m): ρμ(1000)
600m 1000m
S(600)
ρμ(1000)
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Event reconstruction
1. Centre of gravity in ρch distribution →a priori core location
2. Arrival direction optimisation (fitting shower front structure)
3. Core location estimation (fitting lateral distribution)
4. Iterative recalculation of Steps 2 & 3
5. Sθ (600)→S0 (600) translation
6. Energy estimation by S0 (600) vs. E0 relation
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Shower front structure (empirical)
• Modified from Linsley formula – Delay time behind shower plane
Td(R)[ns] = 2.6 ( 1 + R/30[m] )1.5 ρ(R) -0.5
– Shower front thicknessTs(R)[ns] = 2.6 ( 1 + R/30[m] )1.5 ρ(R) -0.3
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Lateral distribution (empirical)
• Modified Linsley formula ρ(R) = C (R/RM) –α (1+R/RM) –(η–α) {1+(R/1000)2} –δ
• C: Normalisation constant, α=1.2, δ=0.6• RM: Moliere unit @ Akeno (=91.6m)• η = (3.97±0.13) – (1.79±0.62) (secθ – 1)
• Fluctuation of observed particle number σρ2 = ρ + 0.25 ρ2 + ρ (= σscin2 + σrest2 + σstat2)
secθ≤1.1
S(600)=10,30[m2]
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Energy estimating relationships• Energy vs. S(600) for vertical showers
– Dai et al.’s MC result by COSMOS+QCDJET (1988)
E0 [eV] = 2.03×1017 S0 (600)
• S(600) Attenuation curve
– Empirical relationship (equi-intensity cut method)
Sθ (600)=S0 (600) ・exp{–X0 / Λ1 (secθ–1) –X0 / Λ2 (secθ–1)2}
• X 0: Atmospheric depth @ AKeno (920 g/cm2)
• Λ 1 = 500 g/cm2
• Λ 2 = 594 g/cm2
2×1019eV1×1019eV
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Event selection criteria (standard)
Dataset: February 1990 – January 2004
1. Energy: ≥1017eV (≥1018.5eV for spectrum)
2. Zenith angle: ≤45°
3. Core location: inside AGASA boundary
4. Number of hit detector ≥ 6
5. Good reconstruction χ2 ≤5 for arrival direction fitting
χ2 ≤1.5 for core location fitting
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Reconstruction accuracy (Energy resolution, Angular resolution)
• Energy resolution– ΔE0/E0=±30% @1019.5eV– ΔE0/E0=±25% @1020eV
• Angular resolution– Δθ=2.0º @1019.5eV– Δθ=1.3º @1020eV
ΔLog(Energy[eV]) –1.0 0.0 –1.0 0.0 1.0
20
15
10
5
0
Cou
nts
[%/b
in]
8
6
4
2
018 19 20
Log(Energy[eV])
90%
68%
Ope
n an
gle
Δθ[
º]
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Exposure (up to May 2003)
• AGASA Exposure – 5.8x1016 m2 sec sr above ~1019eV within θ<45º– AGASA has higher exposure than HiRes below ~3x1019eV
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Core location distribution (>1018.5eV)Before & after unification
Aperture: ~110km2sr extended to ~160 km2sr
’95.12—’04.01
’90.2—’95.12
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Energy spectrum (θ<45º)
• Super GZK-particles exist
– 11events above 1020eV
• Expected 1.9 event on GZK assumption for uniform sources
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Detector calibration
• 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%
Linearity variation (11yr)
Pulse width distri. (~10hr) Gain variation (11yr)
a: Slope
t1:Peak
Cf. Δτ/<τ>=–Δa/<a>
Channel [0.5ns]
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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
Muon / neutrino
Ele. Mag
90%
• 90% primary energy carried by EM component– primary particle & model ~a few % dependence
• S(600) depending less on primary particle / model
AIRES + QGSJET98 / SIBYLL for p & FeEnergy dispersion in atmosphere
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Energy conversion factor
Ref. Model 1ry a b
Dai et al. ’88 COSMOS QCDJET p 2.03 1.02
Single=electron (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
E0 = a [1017eV]x S(600) b
• Presently assigned primary energy: – 10% ±1 2%– Most conservative (We need to push up current energy)
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S(600) attenuation curve
45º
20.0
19.5
19.0
18.5
18.0
AIRES code + QGSJET / SIBYLL model for p / Fe
• 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%
45º
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Shower phenomenology effects(shower front thickness/ delaying particles)
Shower front thicknessParticle arrival time distri. @2km (2x1020eV)
Delaying particles
• Overestimation effects – Important far away from core
• Data between several 100m – 1kmdominant in energy estimation
– Effect of shower front thickness± 5%
– Effect of delaying particles± 5%
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Major systematics in AGASA energy
Detector
Absolute gain ± 0.7%
Linearity ± 7%
Detector response (container, box backscattering)
± 5%
Energy estimator S(600)
Interaction model, primary particles, altitude ± 12%
Shower Phenomenology
Lateral distribution ± 7%
S(600) attenuation ± 5%
Shower front structure ± 5%
Late arriving particles ± 5%
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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Comparison of Ne vs. S(600) in Akeno 1km2 array
• E0 = 8.5×1018 [eV] – by Ne = 5.13×109
• E0 = 9.3×1018 [eV]
– by S(600) = 45.7 [/m2 ]
• E0 [eV] = 3.9×1015(Ne/106) 0.9
– Derived from attenuation curve comparison with Chacalaya (5200m; 540g/cm2) experiment
Fairly good agreement between experiment & MC
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AGASA vs. A1 comparison
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Cosmic ray propagation in Galaxy
• ~1018eV– Well trapped in Galaxy
• >1019eV– Sources extragalactic– >1020eV: Deflection angle ~a few deg.
• Very likely to point back birthplace
1019eV 1020eV1018eV
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Anisotropy around 1018eVSignificance map of event density in 20ºΦ along equi-declination
• Large scale anisotropy clearly found– ~4σ excess @~Galactic Centre – ~4σ deficit @~anti-Galactic Centre
• Evidence of Galactic cosmic rays presence up to 1018eV
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Arrival direction distribution (>1019eV; θ<50º)
• No large scale anisotropy
:>1020eV:1019 – 4x1019eV :4x1019 – 1020eV
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Arrival direction distribution (>4x1019eV; θ<50º)
:4x1019 – 1020eV :>1020eV
• Small scale anisotropy– Event clustering (>4x1019eV within 2.5º)
1 triplet (○) & 6 doublets (○) observed
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Arrival direction distribution (>4x1019eV; θ<50º)
• Small scale anisotropy– Event clustering (>4x1019eV within 2.5º)
1 triplet (○) & 6 doublets (○) observed
– Applying loose criteria (>3.9x1019eV within 2.6º)
2 triplet (doublet → triplet) & 6 doublets (new doublet) observed
:4x1019 – 1020eV :>1020eV
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Arrival direction distribution (>4x1019eV; θ<50º)
• Small scale anisotropy– Event clustering (>4x1019eV within 2.5º)
6 doublets (○) &1 triplet (○) observed • Against expected 2.0 doublets (Pch <0. 1%)• There must be ~ a few x 100 EHECR sources
:4x1019 – 1020eV :>1020eV
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Space angle [º] Space angle [º]
Log E>19.03.4σ
Space angle distribution of events
0 20 40 60
Even
t den
sity
[a.u
.]
0 20 40 60
Even
t den
sity
[a.u
.]
Space angle [º]0 20 40 60
Even
t den
sity
[a.u
.]
Space angle [º]
• Significant peak @ 0 degree– implying presence of compact EHECR sources
Log E>19.23.0σ
Log E>19.42.0σ
Log E>19.64.4σ
0 20 40 60
Even
t den
sity
[a.u
.]
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2D-plots on galactic coordinates
Modelled by Stanev
• Hot region elongating along ~40º tilting from Δb direction– Consistent with Galactic magnetic field structure behind our FOV
Log E >19.0 Log E >19.2
Log E >19.4 Log E >19.6
ΔΔllIIII
ΔΔbbIIII90º<l<180º; –60<b<+60º
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Cluster component
dJ/dE0∝E0–1.8±0.5
Integral EHECR spectrum(Ordinary EHECR vs. cluster comp.)
• Harder spectrum of cluster component
– Scattering lower energy EHECRs
– Watching spectrum at nearby sources?
• Extrapolation meeting highest energy cosmic ray flux @~1020eV
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Chemical composition study
UHECR composition is key discriminator of models ⇒ Muons in giant air shower are key observable for AGASA
• Presence of Super-GZK particles– No location identified as their sources– Possibilities of Top-down models (TDs, Z-burst, SHDM…)
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Gamma-ray shower properties• Fewer muon content (photoproduced muon)• Landau-Pomeranchuk-Migdal (LPM) effect (>~3x1019eV)
– ‘Slowing down’ shower development• Interaction in geomagnetic field (>several x 1019eV)
– ‘Accelerating’ shower development– LPM effect extinction– Incident direction dependence
2000 g/cm2 0 g/cm2
1020eV Gamma-ray (geomag. Interacted)
1020eV Proton
1020eV Gamma-ray (LPM effect)
1000 g/cm2
Simulated with MC by Stanev & Vankov
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Average S(600) vs. energy relationship for gamma-rays (Akeno)
• Gamma-rayenergy underestimation
– 30% @~1019 eV
– 50% @~1019.5 eV(Maximum LPM effct)
– 30% @~1020 eV(Recovered by geomag. effect)
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(R)=C(R/R0)-1.2(1+R/R0)-2.52(1+(R[m]/800)3)-0.6 ,E0=1017.5–1019eV
R0: Characteristic distance (280m @=25o)
Lateral distribution function obtained by A1 Experiment (Hayashida et al. 1995)
Lateral distribution of muons
No significant change in shape of LDM up to 1020eV
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Empirical formulae
Primary mass estimator
Lateral distribution
SAMPLE
Charged particle:
Muon:
• Muon density at 1000m(1000)
– Fitting muon data in R=800-1600m to LDM
– Error~±40%
E0=1.8x1020eV(1000)=2.4[/m2]
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Analysis
• Dataset (After unification in 1995)– E0≥1019eV
– Zenith angle: ≤36º– Normal event quality cuts
– ≥ 2 muon detectors in R=800m–1600m ⇒ (1000)
– Statistics129 events above 1019eV
19 events above 1019.5eV
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Simulations
• Proton / iron primaries (AIRES2.2.1+QGSJET98)
• 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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(1000) distribution (E0>1019eV)
Consistent with proton dominant component
Average relationship (1000)[m−2]= (1.26±0.16)(E0[eV]/1019)0.93±0.13
19 19.5 20 20.5
Log(Energy [eV])
−2
−1
0
1
Log(
Muo
n de
nsity
@10
00m
[m–2
])
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Akeno 1km2 (A1): Hayashida et al. ’95 (Interpretation by AIRES+QGSJET)
Haverah Park (HP): Ave et al. ’03Volcano Ranch (VR): Dova et al. (present conf.)HiRes (HiRes): Archbold et al. (present conf.)
Present result (@90% CL)Fe frac.: <35% (1019 –1019.5 eV) <76% (above 1019.5eV)
Iron fraction(p+Fe 2comp. assumption)
A1: PRELIMINARY
Gradual decrease of Fe fraction
between 1017.5 & 1019eV
A1: Preliminary
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Compilation by Anchordoqui et al. 2004
Fly’s Eye Xmax
MOCCA SIBYLL
Akeno1 μMOCCA + SIBYLL
Volcano R. Lat.QGSJET98
Haverah P T50QGSJET01
HiRes Xmax
CORSIKA QGSJET
AGASA μAIRES QGSJET98
Akeno1 μAIRES + QGSJET98
HiRes-MIA Xmax
CORSIKA QGSJET
Haverah P. Lat.QGSJET98
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Limits on gamma-ray fraction
• Gamma-ray fraction upper limits (@90%CL)
to observed events
– 34% (>1019eV)(/p<0.45)
– 56% (>1019.5eV)(/p<1.27)
Topological defects (Sigl et al. ‘01) (Mx=1016[eV]; flux normalised@1020eV )
Z-burst model(Sigl et al. ‘01)(Flux normalised@1020eV)
SHDM-model (Berezinski ‘03) (Mx=1014[eV]; flux normalised@1020eV )
Assuming 2-comp. (p+gamma-ray) primaries
SHDM-model (Berezinski et al. ‘98) (Mx=1014[eV]; flux normalised@1019eV )
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Summary• Energy Spectrum
– 11 events observed >1020eV against 1.9 on GZK assumption – Energy spectrum remains extending beyond GZK cut-off
Conventional GZK mechanism can hardly explain!!
• Arrival direction distribution– Signature of compact EHECR sources
• 6 doublets & 1 triplet in 2.5º above 4x1019eV (θ<50 º)– Feature of charged EHECRs deflection in GMF
• Chemical composition– Gradual lightening between 1017.5 & 1019eV– Light component favoured @1019eV (AIRES+QGSJET)– Gamma-ray dominance negative at highest energies
Fraction of gamma-rays <56% @90%CL (> 1019.5eV)
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Outlook (what’s gonna come to India)
• Energy spectrum – Data analysis up to 60º zenith angle– Improved energy estimation
• Arrival direction distribution– Data analysis up to 60º zenith angles– Improved understanding shower front stucture– Detailed features in anisotropy
• Chemical composition– Interpretation using latest MC simulations
• Akeno 1km2 data – Data interpretation of old Akeno 1km2 data by latest MCs– Energy spectrum & chemical composition in 1016—1018eV en
ergies