Results of AGASA Experiment __Energy spectrum & Chemical composition __ Kenji SHINOZAKI...

Results of AGASA ExperimentResults of AGASA Experiment__Energy spectrum & Chemical composition ____Energy spectrum & Chemical composition __

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

The Highest Energy Cosmic Rays and Their Sources21 – 23 May, 2004 @INR Moscow

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

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 / 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 γCMB → N π+

(E0 ~5x1019eV)

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 ~ 250 EHECR sources (185–340)

:4x1019 – 1020eV :>1020eV

Log E>19.03.4σ

Space angle distribution of events

• Significant peak @ 0 degree– implying presence of compact EHECR sources

Log E>19.64.4σ

• 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

• 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

AGASA Collaborators

Japan

Federal Republic of Germany

United States of America

Akeno Observatory– Inst. for Cosmic Ray Research, Univ. of Tokyo– Akeno,Yamanashi Japan (100km west of Tokyo)– Lat. 35º47’N, Long. 138º30’E Altitude 900m– Atom. depth 920 g/cm2

– Ave. pressure 910hPa– Temp. –10 —　+30℃

Muon detectorstation

× Tokyo東京

Vladivostok ×ウラジオストク

Yakutsk ×ヤクーツク Sea of Okho

tskオホーツク

海

Pacific Ocean太平洋

TA Prototype

Tsukubaつくば

×

Akeno明野

× M

ｔ .Fuji富士山

Leadburger

Main Building

Cosmic Ray Imaging System AUGER Water Tank

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. 1990–Dec.1995

4 separate-array operation– Dec. 1995–Jan.2004

Unified operation

SB

NB

AB

TB

• Surface detector– 5cm thick 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

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

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]

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

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

Event sample

Event sample

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

Core location distribution (>1018.5eV)Before & after unification

Aperture: ~110km2sr extended to ~160 km2sr

’95.12—’04.01

’90.2—’95.12

Exposure (up to May 2003)

• AGASA Exposure – 5.4x1016 m2 sec sr above ~1019eV within θ<45º– AGASA has higher exposure than HiRes below ~3x1019eV

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]

Energy spectrum (θ<45º)

• Super GZK-particles exist

– 11events above 1020eV

• Expected 1.9 event on GZK assumption for uniform sources

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]

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

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

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)

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

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% ± 5%

– Effect of delaying particles+5% ± 5%

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 –10% ± 12%

Shower Phenomenology

Lateral distribution ± 7%

S(600) attenuation ± 5%

Shower front structure +5% ± 5%

Late arriving particles +5% ± 5%

Total ± 18%

Systematics is energy independent above 1019eVFeature 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

Recent spectra (AGASA vs. HiRes@Tsukuba ICRC)

HiRes: Bergman et al. ’03

• ~2.5 sigma discrepancy between AGASA & HiRes

• Energy scale difference by 25% vs. HiRes-stereo

vs. HiRes-I

vs. HiRes-II

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

AGASA vs. A1 comparison

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…)

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/cm2500 g/cm2

1020eV Gamma-ray (geomag. Interacted)

1020eV Proton

1020eV Gamma-ray (LPM effect)

1000 g/cm2

Simulated with MC by Stanev & Vankov

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)

(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

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]

Analysis

• Dataset (13 December 1995 – 31 December 2002)

– 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

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

(1000) distribution (E0>1019eV)

Average relationship (1000)[m−2]= (1.26±0.16)(E0[eV]/1019)0.93±0.13

Consistent with proton dominant component

19 19.5 20 20.5

Log(Energy [eV])

−2

−1

0

1

Log(

Muo

n de

nsity

@10

00m

[m–2

])

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 VERY PRELIMINARY

A1: Preliminary

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 )

Summary• AGASA operation

– 14year-observation watching 17km2 century sr exposure @ >95% live-ratio

• Systematic errors in energy determination– ±18% independent of energy (≥1019eV)

• Super-GZK particles do exist– 11 events observed >1020eV against 1.9 on GZK assumption – Energy spectrum remains extending beyond GZK cut-off

Conventional GZK mechanism can hardly explain!!

• 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) (AIRES+QGSJET)

Another approach (Energy underestimation for gamma-rays)

• Effects on UHE Gamma-ray

– LPM effect (>3x1019eV)

– Geomagnetic effect (>5x1019eV)

• 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@Rubtsov’s talk