Transcript AGASA Results

Results of Experiments in Akeno
Kenji SHINOZAKI
Max-Planck-Institut für Physik (Werner-Heisenberg-Institut)
Munich, Germany
on behalf of AGASA Collaboration
2nd International Workshop on Ultra-high-energy cosmic rays and their sources
14 – 16 April, 2005 @INR Moscow
AGASA Collaborators
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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
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RIKEN (Wako)
– Yoshiya Kawasaki, Hirohiko M. Shimizu Chiba
University (Chiba)
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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
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Max-Planck-Institute for Physics (Munich, GER)
– Kenji Shinozaki, Masahiro Teshima
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National Institute of Radiological Sciences (Chiba)
– Yukio Uchihori
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University of Chicago (Chicago, USA)
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Tokonatsu Yamamoto
Physics motivation
• Understanding nature & origin of
UHECRs (>1019eV)
– Energy spectrum
– Arrival direction distribution
– Chemical composition
• Super GZK particles
incl. 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)
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)
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
Pre-AGASA
AGASA
AGASA era
AGASA
AGASA (Akeno Giant Air Shower Array)
• Detector station
– 111 surface detectors
TB
• Effective area ~100km2
• Optical fibre cable
connection to observatory
• Triggered by 5-neighbouring
hit detector within 25ms
– 27 muon detectors
• Southern region
~30km2 coverage
• Operation
– Feb. 1990–Dec.1995
4 separate-array operation
– Dec. 1995–Jan.2004
Unified operation
NB
SB
AB
• 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
Event sample & observables
4.11x1019eV
S(600)
ρμ(1000)
600m 1000m
• 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)
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
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 thickness
Ts(R)[ns] = 2.6 ( 1 + R/30[m] )1.5 ρ(R) -0.3
Lateral distribution (empirical)
secθ≤1.1
S(600)=10,30[m2]
• 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)
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
2×1019eV
1×1019eV
– 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
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
Reconstruction accuracy
(Energy resolution, Angular resolution)
8
Open angle Δθ[º]
Counts [%/bin]
20
15
10
5
0
–1.0 0.0 –1.0
6
4
2
68%
0
0.0
1.0
ΔLog(Energy[eV])
• Energy resolution
– ΔE0/E0=±30% @1019.5eV
– ΔE0/E0=±25% @1020eV
90%
18
19
20
Log(Energy[eV])
• Angular resolution
– Δθ=2.0º @1019.5eV
– Δθ=1.3º @1020eV
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
Core location distribution (>1018.5eV)
Before & after unification
’90.2—’95.12
Aperture: ~110km2sr
’95.12—’04.01
extended to
~160 km2sr
Energy spectrum
(θ<45º)
• Super GZK-particles exist
– 11events above 1020eV
• Expected 1.9 event
on GZK assumption for uniform sources
Detector calibration
t1:Peak
Pulse width distri. (~10hr)
Gain variation (11yr)
a: Slope
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. Δτ/<τ>=–Δa/<a>
Linearity variation (11yr)
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
Energy conversion
AIRES + QGSJET98 / SIBYLL for p & Fe
Energy dispersion in atmosphere
Muon / neutrino
90%
Ele. Mag
• 90% primary energy carried by EM component
– primary particle & model ~a few % dependence
• S(600) depending less on primary particle / model
Energy conversion factor
E0 = a [1017eV]x S(600) b
Ref.
Dai et al. ’88 COSMOS
Model
1ry
a
b
QCDJET
p
2.03
1.02
QGSJET98
p
2.07
1.03
Fe
2.34
1.00
p
2.30
1.03
Fe
2.19
1.03
p
2.17
1.01
Fe
2.15
1.03
p
2.34
1.04
Fe
2.24
1.02
Single=electron (900m)
Nagano et al. ’99 (CORSIKA5.621)
Single= PH peak (900m)
SIBYLL1.6
Sakaki et al. ’01 (AIRES2.2.1)
QGSJET98
Single= PW peak (667m)
SIBYLL1.6
• Presently assigned primary energy: – 10% ±1 2%
– Most conservative (We need to push up current energy)
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%
Shower phenomenology effects
(shower front thickness/ delaying particles)
Particle arrival time distri. @2km (2x1020eV)
Shower front thickness
• Overestimation effects
– Important far away from core
• Data between several 100m – 1km
dominant in energy estimation
– Effect of shower front thickness
± 5%
– Effect of delaying particles
± 5%
Delaying particles
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.
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
Comparison of Ne vs. S(600) in Akeno 1km2 array
• E0 [eV] = 3.9×1015(Ne/106) 0.9
– Derived from attenuation curve
comparison with Chacalaya (5200m; 540g/cm2) experiment
• E0 = 8.5×1018 [eV]
– by Ne = 5.13×109
• E0 = 9.3×1018 [eV]
– by S(600) = 45.7 [/m2 ]
Fairly good agreement
between experiment & MC
AGASA vs. A1 comparison
Cosmic ray propagation in Galaxy
1018eV
1019eV
• ~1018eV
– Well trapped in Galaxy
• >1019eV
– Sources extragalactic
– >1020eV: Deflection angle ~a few deg.
• Very likely to point back birthplace
1020eV
Anisotropy around 1018eV
Significance 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
Arrival direction distribution
(>1019eV; θ<50º)
:1019 – 4x1019eV
:4x1019 – 1020eV
:>1020eV
• No large scale anisotropy
Arrival direction distribution
(>4x1019eV; θ<50º)
:4x1019 – 1020eV
• Small scale anisotropy
– Event clustering (>4x1019eV within 2.5º)
1 triplet (○) & 6 doublets (○) observed
:>1020eV
Arrival direction distribution
(>4x1019eV; θ<50º)
:4x1019 – 1020eV
:>1020eV
• 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
Arrival direction distribution
(>4x1019eV; θ<50º)
:4x1019 – 1020eV
:>1020eV
• 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
Event density [a.u.]
0
0
Event density [a.u.]
Log E>19.0
3.4σ
20
40
Space angle [º]
60
Log E>19.4
2.0σ
20
40
Space angle [º]
60
0
Log E>19.2
3.0σ
20
40
Space angle [º]
Event density [a.u.]
Event density [a.u.]
Space angle distribution of events
0
60
Log E>19.6
4.4σ
20
40
Space angle [º]
60
• Significant peak @ 0 degree
– implying presence of compact EHECR sources
2D-plots on galactic coordinates
90º<l<180º; –60<b<+60º
ΔbII
Log E >19.0
Log E >19.2
ΔlII
Log E >19.4
Log E >19.6
Modelled by Stanev
• Hot region elongating along ~40º tilting from Δb direction
– Consistent with Galactic magnetic field structure behind our FOV
Integral EHECR spectrum
(Ordinary EHECR vs. cluster comp.)
Cluster component
dJ/dE0∝E0–1.8±0.5
• Harder spectrum of cluster component
– Scattering lower energy EHECRs
– Watching spectrum at nearby sources?
• Extrapolation meeting highest energy cosmic ray flux @~1020eV
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
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
Simulated with MC by Stanev & Vankov
1020eV Proton
1020eV Gamma-ray
(LPM effect)
1020eV Gamma-ray
(geomag. Interacted)
2000 g/cm2
1000 g/cm2
0 g/cm2
Average S(600) vs. energy relationship
for gamma-rays (Akeno)
• Gamma-ray
energy underestimation
– 30% @~1019 eV
– 50% @~1019.5 eV
(Maximum LPM effct)
– 30% @~1020 eV
(Recovered by geomag. effect)
Lateral distribution of muons
No significant change in shape of LDM up to 1020eV
rm(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 @q=25o)
Lateral distribution function obtained by A1 Experiment (Hayashida et al. 1995)
Primary mass estimator
E0=1.8x1020eV
rm(1000)=2.4[/m2]
Lateral distribution
SAMPLE
• Muon density at 1000m
rm(1000)
– Fitting muon data
in R=800-1600m to LDM
– Error~±40%
Muon:
Charged particle:
Empirical formulae
Analysis
• Dataset (After unification in 1995)
– E0≥1019eV
– Zenith angle: q≤36º
– Normal event quality cuts
– ≥ 2 muon detectors in R=800m–1600m ⇒ rm(1000)
– Statistics
129 events above 1019eV
19 events above 1019.5eV
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
rm(1000) distribution (E0>1019eV)
Consistent with proton dominant component
Log(Muon density@1000m[m–2])
Average relationship rm (1000)[m−2]= (1.26±0.16)(E0[eV]/1019)0.93±0.13
1
0
−1
−2
19
19.5
20
Log(Energy [eV])
20.5
Iron fraction
(p+Fe 2comp. assumption)
A1: Preliminary
A1: PRELIMINARY
Present result (@90% CL)
Fe frac.: <35% (1019 –1019.5 eV)
<76% (above 1019.5eV)
Akeno 1km2 (A1): Hayashida et al. ’95
(Interpretation by AIRES+QGSJET)
Gradual decrease of Fe fraction
between 1017.5 & 1019eV
Haverah Park (HP): Ave et al. ’03
Volcano Ranch (VR): Dova et al. (present conf.)
HiRes (HiRes): Archbold et al. (present conf.)
Compilation by Anchordoqui et al. 2004
Fly’s Eye Xmax
MOCCA SIBYLL
Akeno1 μ
MOCCA + SIBYLL
Volcano R. Lat.
Haverah P T50
QGSJET01
QGSJET98
Haverah P. Lat.
QGSJET98
HiRes-MIA Xmax
AGASA μ
CORSIKA QGSJET
AIRES QGSJET98
HiRes Xmax
Akeno1 μ
CORSIKA QGSJET
AIRES + QGSJET98
Limits on gamma-ray fraction
Assuming 2-comp.
(p+gamma-ray) primaries
• Gamma-ray fraction
upper limits (@90%CL)
to observed events
– 34% (>1019eV)
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 )
SHDM-model (Berezinski et al. ‘98)
(Mx=1014[eV]; flux normalised@1019eV )
(g/p<0.45)
– 56% (>1019.5eV)
(g/p<1.27)
• Energy Spectrum
Summary
– 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)
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
energies