2. Results of Experiments in Akeno Kenji SHINOZAKI Max-Planck-Institut für Physik (Werner-Heisenberg-Institut) Munich, Germany Max-Planck-Institut für 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

3. 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 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 AGASA Collaborators We are INTERCONTINETAL collaboration among 31 (all Japanese) scientists from 17 institutes in 3 nations

4. Physics motivation Understanding nature & origin of UHECRs (>10 19 eV) –Energy spectrum –Arrival direction distribution –Chemical composition Super GZK particles incl. highest energy cosmic rays (>10 20 eV) –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, p UHECR γ CMB → N π + (E 0 ~5x10 19 eV)

5. 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)

6. Outline Physics motivation & observation principle Activities at Akeno Observatory Energy determination & spectrum –Shower properties & analysis –Systematic error in energy estimation UHECR Anisotropy –10 18 eV energies –10 19 eV energy and Super-GZK Muon component & chemical composition Summary & outlook

7. Pre-AGASA AGASA

8. AGASA era AGASA

9. AGASA (Akeno Giant Air Shower Array) ~8km Detector station –111 surface detectors Effective area ~100km 2 Optical fibre cable connection to observatory Triggered by 5-neighbouring hit detector within 25  s –27 muon detectors Southern region ~30km 2 coverage Operation –Feb. 1990–Dec.1995 4 separate-array operation –Dec. 1995–Jan.2004 Unified operation SB NB AB TB

10. Surface detector –5cm thick plastic scintillator –Hamamatsu 5” R1512 PMT Muon detectors (2.8–10m 2 ;south region) –14–20 Proportional counters –Shielded by 30cm Fe or 1m concrete Threshold energy: 0.5GeVxsecθ –Triggered by accompanying surface detector

12. Event sample & observables 4.11x10 19 eV Energy estimator (charged particle density @600m): S(600) E 0 = 2.0 × 10 17 S(600) for vertical showers → less dependent of 1ries or interaction models Primary mass estimator (muon density@1000m): ρ μ (1000) 600m1000m S(600) ρμ(1000)

13. Event reconstruction 1.Centre of gravity in ρ ch 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. S θ (600)→S 0 (600) translation 6.Energy estimation by S 0 (600) vs. E 0 relation

14. Shower front structure (empirical) Modified from Linsley formula –Delay time behind shower plane T d (R) [ns] = 2.6 ( 1 + R/30 [m] ) 1.5 ρ(R) -0.5 –Shower front thickness T s (R) [ns] = 2.6 ( 1 + R/30 [m] ) 1.5 ρ(R) -0.3

15. Lateral distribution (empirical) Modified Linsley formula ρ(R) = C (R/R M ) –α (1+R/R M ) –(η–α) {1+(R/1000) 2 } –δ C: Normalisation constant, α=1.2, δ=0.6 R M : Moliere unit @ Akeno (=91.6m) η = (3.97±0.13) – (1.79±0.62) (secθ – 1) Fluctuation of observed particle number σ ρ 2 = ρ + 0.25 ρ 2 + ρ (= σ scin 2 + σ rest 2 + σ stat 2 ) secθ≤1.1 S(600)=10,30[m 2 ]

16. Energy estimating relationships Energy vs. S(600) for vertical showers –Dai et al.’s MC result by COSMOS+QCDJET (1988) E 0 [eV] = 2.03×10 17 S 0 (600) S(600) Attenuation curve –Empirical relationship (equi-intensity cut method) S θ (600)=S 0 (600) ・ exp{–X 0 / Λ 1 (secθ–1) –X 0 / Λ 2 (secθ–1) 2 } X 0 : Atmospheric depth @ AKeno (920 g/cm 2 ) Λ 1 = 500 g/cm 2 Λ 2 = 594 g/cm 2 2×10 19 eV 1×10 19 eV

17. Event selection criteria (standard) Dataset: February 1990 – January 2004 1.Energy: ≥10 17 eV (≥10 18.5 eV for spectrum) 2.Zenith angle: ≤45° 3.Core location: inside AGASA boundary 4.Number of hit detector ≥ 6 5.Good reconstruction χ 2 ≤5for arrival direction fitting χ 2 ≤1.5for core location fitting

18. Reconstruction accuracy (Energy resolution, Angular resolution) Energy resolution –ΔE 0 /E 0 =±30% @10 19.5 eV –ΔE 0 /E 0 =±25% @10 20 eV Angular resolution –Δθ=2.0º @10 19.5 eV –Δθ=1.3º @10 20 eV ΔLog(Energy[eV]) –1.0 0.0 –1.0 0.0 1.0 20 15 10 5 0 Counts [%/bin] 8 6 4 2 0 18 19 20 Log(Energy[eV]) 90% 68% Open angle Δθ[º]

19. Exposure (up to May 2003) AGASA Exposure –5.8x10 16 m 2 sec sr above ~10 19 eV within θ<45º –AGASA has higher exposure than HiRes below ~3x10 19 eV AGASA detector

20. Core location distribution (>10 18.5 eV) Before & after unification Aperture: ~110km 2 sr extended to ~160 km 2 sr ’95.12—’04.01’90.2—’95.12

21. Energy spectrum (θ<45º) Super GZK-particles exist –11events above 10 20 eV Expected 1.9 event on GZK assumption for uniform sources

22. 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 t 1 :Peak Cf. Δτ/ =–Δa/ Channel [0.5ns]

23. 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

24. 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 & Fe Energy dispersion in atmosphere

25. Energy conversion factor Ref.Model1ryab Dai et al. ’88 COSMOSQCDJETp2.031.02 Single=electron (900m) Nagano et al. ’99 (CORSIKA5.621)QGSJET98p2.071.03 Single= PH peak (900m)Fe2.341.00 SIBYLL1.6p2.301.03 Fe2.191.03 Sakaki et al. ’01 (AIRES2.2.1)QGSJET98p2.171.01 Single= PW peak (667m)Fe2.151.03 SIBYLL1.6p2.341.04 Fe2.241.02 E 0 = a [10 17 eV]x S(600) b Presently assigned primary energy: – 10% ±1 2% –Most conservative (We need to push up current energy)

26. 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

27. Shower phenomenology effects (shower front thickness/ delaying particles) Shower front thickness Particle arrival time distri. @2km (2x10 20 eV) Delaying particles 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%

28. 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 10 19 eV Feature of spectrum can hardly change that extends beyond GZK cutoff.

29. 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

30. Comparison of N e vs. S(600) in Akeno 1km 2 array E 0 = 8.5×10 18 [eV] –by N e = 5.13×10 9 E 0 = 9.3×10 18 [eV] –by S(600) = 45.7 [/m 2 ] E 0 [eV] = 3.9×10 15 (N e /10 6 ) 0.9 –Derived from attenuation curve comparison with Chacalaya (5200m; 540g/cm 2 ) experiment Fairly good agreement between experiment & MC

31. AGASA vs. A1 comparison

32. Cosmic ray propagation in Galaxy ~10 18 eV –Well trapped in Galaxy >10 19 eV –Sources extragalactic –>10 20 eV: Deflection angle ~a few deg. Very likely to point back birthplace 10 19 eV 10 20 eV 10 18 eV

33. Anisotropy around 10 18 eV 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 10 18 eV

34. Arrival direction distribution (>10 19 eV; θ<50º) No large scale anisotropy :>10 20 eV:10 19 – 4x10 19 eV:4x10 19 – 10 20 eV

35. Arrival direction distribution (>4x10 19 eV; θ<50º) :4x10 19 – 10 20 eV:>10 20 eV Small scale anisotropy –Event clustering (>4x10 19 eV within 2.5º) 1 triplet (○) & 6 doublets (○) observed

36. Arrival direction distribution (>4x10 19 eV; θ<50º) Small scale anisotropy –Event clustering (>4x10 19 eV within 2.5º) 1 triplet (○) & 6 doublets (○) observed –Applying loose criteria (>3.9x10 19 eV within 2.6º) 2 triplet (doublet → triplet) & 6 doublets (new doublet) observed :4x10 19 – 10 20 eV:>10 20 eV

37. Arrival direction distribution (>4x10 19 eV; θ<50º) Small scale anisotropy –Event clustering (>4x10 19 eV within 2.5º) 6 doublets (○) &1 triplet (○) observed Against expected 2.0 doublets (P ch <0. 1%) There must be ~ a few x 100 EHECR sources :4x10 19 – 10 20 eV:>10 20 eV

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

39. 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 >19.4Log E >19.6 Δl II Δ b II 90º<l<180º; –60<b<+60º

40. Cluster component dJ/dE 0 ∝ E 0 –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 @~10 20 eV

41. 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…)

42. Gamma-ray shower properties Fewer muon content (photoproduced muon) Landau-Pomeranchuk-Migdal (LPM) effect (>~3x10 19 eV) –‘Slowing down’ shower development Interaction in geomagnetic field (>several x 10 19 eV) –‘Accelerating’ shower development –LPM effect extinction –Incident direction dependence 2000 g/cm 2 0 g/cm 2 10 20 eV Gamma-ray (geomag. Interacted) 10 20 eV Proton 10 20 eV Gamma-ray (LPM effect) 1000 g/cm 2 Simulated with MC by Stanev & Vankov

43. Average S(600) vs. energy relationship for gamma-rays (Akeno) Gamma-ray energy underestimation –30% @~10 19 eV –50% @~10 19.5 eV (Maximum LPM effct) –30% @~10 20 eV (Recovered by geomag. effect)

44.    (R)=C(R/R 0 ) -1.2 (1+R/R 0 ) -2.52 (1+(R[m]/800) 3 ) -0.6,E 0 =10 17.5 –10 19 eV R 0 : Characteristic distance (280m @  =25 o ) Lateral distribution function obtained by A1 Experiment (Hayashida et al. 1995) Lateral distribution of muons No significant change in shape of LDM up to 10 20 eV

45. 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% E 0 =1.8x10 20 eV   (1000)=2.4[/m 2 ] Muon density@1000m  µ (1000) –~20% to total charged particles –Feasible mass estimator for UHECRs

46. Analysis Dataset (After unification in 1995) –E 0 ≥10 19 eV –Zenith angle:  ≤36º –Normal event quality cuts – ≥ 2 muon detectors in R=800m–1600m ⇒   (1000) –Statistics 129 events above 10 19 eV 19 events above 10 19.5 eV

47. Simulations Proton / iron primaries (AIRES2.2.1+QGSJET98) Gamma-ray primaries (Geomag. + AIRES +LPM) –Geomagnetic field effect Significant above 10 19.5 eV Code by Stanev &Vankov –LPM effect Significant above 10 19.0 eV Included in AIRES Detector configuration & analysis process

48.   (1000) distribution (E 0 >10 19 eV) Consistent with proton dominant component Average relationship    (1000)[m −2 ]= (1.26±0.16)(E 0 [eV]/10 19 ) 0.93±0.13 1919.52020.5 Log(Energy [eV]) −2−2 −1−1 0 1 Log(Muon density@1000m[m –2 ])

49. Akeno 1km 2 (A1): Hayashida et al. ’95 (Interpretation by AIRES+QGSJET) Haverah Park (HP): Ave et al. ’03 Volcano Ranch (VR): Dova et al. (present conf.) HiRes (HiRes): Archbold et al. (present conf.) Present result (@90% CL) Fe frac.: <35% (10 19 –10 19.5 eV) <76% (above 10 19.5 eV) Iron fraction (p+Fe 2comp. assumption) A1: PRELIMINARY Gradual decrease of Fe fraction between 10 17.5 & 10 19 eV A1: Preliminary

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

51. Limits on gamma-ray fraction Gamma-ray fraction upper limits (@90%CL) to observed events – 34% (>10 19 eV) (  /p<0.45) –56% (>10 19.5 eV) (  /p<1.27) Topological defects (Sigl et al. ‘01) (M x =10 16 [eV]; flux normalised@10 20 eV ) Z-burst model(Sigl et al. ‘01) (Flux normalised@10 20 eV) SHDM-model (Berezinski ‘03) (Mx=10 14 [eV]; flux normalised@10 20 eV ) Assuming 2-comp. (p+gamma-ray) primaries SHDM-model (Berezinski et al. ‘98) (Mx=10 14 [eV]; flux normalised@10 19 eV )

52. Summary Energy Spectrum –11 events observed >10 20 eV 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 4x10 19 eV (θ<50 º) –Feature of charged EHECRs deflection in GMF Chemical composition –Gradual lightening between 10 17.5 & 10 19 eV –Light component favoured @10 19 eV (AIRES+QGSJET) –Gamma-ray dominance negative at highest energies Fraction of gamma-rays 10 19.5 eV) Step toward EHECR astronomy!!

53. 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 A keno 1km 2 data –Data interpretation of old Akeno 1km 2 data by latest MCs –Energy spectrum & chemical composition in 10 16 —10 18 eV energies Step toward EHECR astronomy!!