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Results of Experiments in Akeno

Results of Experiments in Akeno. Kenji SHINOZAKI Max-Planck-Institut f ü r Physik (Werner-Heisenberg-Institut) Munich, Germany on behalf of AGASA Collaboration. 2 nd International Workshop on Ultra-high-energy cosmic rays and their sources 14 – 16 April, 2005 @ INR Moscow.

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Results of Experiments in Akeno

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  1. Results of Experiments in Akeno Kenji SHINOZAKI Max-Planck-Institut für Physik(Werner-Heisenberg-Institut)Munich, Germanyon behalf of AGASA Collaboration 2nd International Workshop on Ultra-high-energy cosmic rays and their sources 14 – 16 April, 2005 @INR Moscow

  2. AGASA Collaborators • RIKEN (Wako) • Yoshiya Kawasaki, Hirohiko M. Shimizu Chiba University (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 • 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 We are INTERCONTINETAL collaborationamong 31 (all Japanese) scientists from 17 institutes in 3 nations

  3. 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-Downscenarios • Topological defects • Super heavy dark matter • Z-burst⇒ Gamma-ray + nucleon 1ries predicted • Source location still not identified, pUHECRγCMB → N π+(E0 ~5x1019eV)

  4. 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)

  5. 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

  6. Pre-AGASA AGASA

  7. AGASA era AGASA

  8. TB NB SB AB 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 25ms • 27 muon detectors • Southern region ~30km2 coverage • Operation • Feb. 1990–Dec.19954 separate-array operation • Dec. 1995–Jan.2004 Unified operation ~8km

  9. 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

  10. Event sample & observables 4.11x1019eV S(600) ρμ(1000) 600m 1000m • Energy estimator (charged particle density @600m): S(600)E0 = 2.0 × 1017S(600) for vertical showers→ less dependent of 1ries or interaction models • Primary mass estimator (muon density@1000m): ρμ(1000)

  11. Event reconstruction • Centre of gravity in ρch distribution →a priori core location • Arrival direction optimisation (fitting shower front structure) • Core location estimation (fitting lateral distribution) • Iterative recalculation of Steps 2 & 3 • Sθ (600)→S0 (600) translation • Energy estimation by S0(600) vs. E0 relation

  12. Shower front structure (empirical) • Modified from Linsley formula • Delay time behind shower planeTd(R)[ns] = 2.6 ( 1 + R/30[m] )1.5ρ(R) -0.5 • Shower front thicknessTs(R)[ns] = 2.6 ( 1 + R/30[m] )1.5ρ(R) -0.3

  13. Lateral distribution (empirical) • Modified Linsley formulaρ(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]

  14. 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

  15. 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 χ2≤5 for arrival direction fitting χ2≤1.5 for core location fitting

  16. 8 20 6 15 Open angle Δθ[º] 4 Counts [%/bin] 10 90% 5 2 68% 0 0 18 19 20 –1.0 0.0 –1.0 0.0 1.0 ΔLog(Energy[eV]) Log(Energy[eV]) 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

  17. 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 AGASA detector

  18. Core location distribution (>1018.5eV)Before & after unification ’90.2—’95.12 ’95.12—’04.01 Aperture: ~110km2sr extended to ~160 km2sr

  19. Energy spectrum (θ<45º) • Super GZK-particles exist • 11events above 1020eV • Expected 1.9 event on GZK assumption for uniform sources

  20. Detector calibration t1:Peak Pulse width distri. (~10hr) Gain variation (11yr) • 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% a: Slope Linearity variation (11yr) Channel [0.5ns] Cf. Δτ/<τ>=–Δa/<a>

  21. 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

  22. Muon / neutrino Ele. Mag 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

  23. Energy conversion factor E0 = a [1017eV]x S(600)b • Presently assigned primary energy: –10% ±1 2% • Most conservative (We need to push up current energy)

  24. 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%

  25. 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 – 1kmdominant in energy estimation • Effect of shower front thickness± 5% • Effect of delaying particles± 5% Delaying particles

  26. Major systematics in AGASA energy Systematics is energy independent above 1019eV Feature of spectrum can hardly change that extends beyond GZK cutoff.

  27. 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

  28. 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

  29. AGASA vs. A1 comparison

  30. Cosmic ray propagation in Galaxy 1018eV 1019eV 1020eV • ~1018eV • Well trapped in Galaxy • >1019eV • Sources extragalactic • >1020eV: Deflection angle ~a few deg. • Very likely to point back birthplace

  31. 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

  32. Arrival direction distribution(>1019eV; θ<50º) :1019 – 4x1019eV :4x1019 – 1020eV :>1020eV • No large scale anisotropy

  33. Arrival direction distribution (>4x1019eV; θ<50º) :4x1019 – 1020eV :>1020eV • Small scale anisotropy • Event clustering (>4x1019eV within 2.5º) 1 triplet (○) & 6 doublets (○) observed

  34. 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

  35. 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

  36. Space angle distribution of events Log E>19.0 3.4σ Log E>19.2 3.0σ Event density [a.u.] Event density [a.u.] 0 20 40 60 0 20 40 60 Space angle [º] Space angle [º] Log E>19.4 2.0σ Log E>19.6 4.4σ Event density [a.u.] Event density [a.u.] 0 20 40 60 0 20 40 60 Space angle [º] Space angle [º] • Significant peak @ 0 degree • implying presence of compact EHECR sources

  37. 2D-plots on galactic coordinates 90º<l<180º; –60<b<+60º ΔbII Log E >19.2 Log E >19.0 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

  38. 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

  39. 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

  40. 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

  41. 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)

  42. 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)

  43. Primary mass estimator E0=1.8x1020eV rm(1000)=2.4[/m2] • Muon density at 1000mrm(1000) • Fitting muon data in R=800-1600m to LDM • Error~±40% Lateral distribution SAMPLE Muon: Empirical formulae Charged particle: • Muon density@1000m rµ(1000) • ~20% to total charged particles • Feasible mass estimatorfor UHECRs

  44. 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

  45. 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

  46. Average relationship rm(1000)[m−2]= (1.26±0.16)(E0[eV]/1019)0.93±0.13 1 0 Log(Muon density@1000m[m–2]) −1 −2 19 19.5 20 20.5 Log(Energy [eV]) rm(1000) distribution (E0>1019eV) Consistent with proton dominant component

  47. Iron fraction(p+Fe 2comp. assumption) Akeno 1km2 (A1):Hayashida et al. ’95 (Interpretation by AIRES+QGSJET) A1: Preliminary Present result (@90% CL)Fe frac.: <35% (1019–1019.5eV)<76% (above 1019.5eV) A1: PRELIMINARY 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.)

  48. Compilation by Anchordoqui et al. 2004 Fly’s Eye Xmax MOCCA SIBYLL Haverah P T50 QGSJET01 Akeno1 μ MOCCA + SIBYLL Volcano R. Lat. QGSJET98 Haverah P. Lat. QGSJET98 HiRes-MIA Xmax CORSIKA QGSJET AGASA μ AIRES QGSJET98 HiRes Xmax CORSIKA QGSJET Akeno1 μ AIRES + QGSJET98

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