Interpretation of the Cosmic-ray Energy

Spectrum and the Knee Inferred from the Tibet Air-Shower Experiment

M.Shibata*

and

Tibet ASg Collaboration

*Yokohama National University

ICRC2009 Lodz, Poland

The Tibet AS Collaboration

M.Amenomori(1), X.J.Bi(2), D.Chen(3), S.W.Cui(4), Danzengluobu(5), L.K.Ding(2), X.H.Ding(5), C.Fan(6), C.F.Feng(6), Zhaoyang Feng(2), Z.Y.Feng(7), X.Y.Gao(8), Q.X.Geng(8), Q.B.Gou(2), H.W.Guo(5), H.H.He(2), M.He(6), K.Hibino(9), N.Hotta(10), Haibing Hu(5), H.B.Hu(2), J.Huang(2), Q.Huang(7), H.Y.Jia(7), L.Jiang(8, 2), F.Kajino(11), K.Kasahara(12), Y.Katayose(13), C.Kato(14), K.Kawata(3), Labaciren(5), G.M.Le(15), A.F.Li(6), H.C.Li(4, 2), J.Y.Li(6), C.Liu(2), Y.-Q.Lou(16), H.Lu(2), X.R.Meng(5), K.Mizutani(12, 17), J.Mu(8), K.Munakata(14), A.Nagai(18), H.Nanjo(1), M.Nishizawa(19), M.Ohnishi(3), I.Ohta(20), S.Ozawa(12), T.Saito(21), T .Y.Saito(22), M.Sakata(11), T.K.Sako(3), M.Shibata(13), A.Shiomi(23), T.Shirai(9), H.Sugimoto(24), M.Takita(3), Y.H.Tan(2), N.Tateyama(9), S.Torii(12), H.Tsuchiya(25), S.Udo(9), B.Wang(2), H.Wang(2), Y.Wang(2), Y.G.Wang(6), H.R.Wu(2),L.Xue(6), Y.Yamamoto(11), C.T.Yan(26), X.C.Yang(8), S.Yasue(27), Z.H.Ye(28), G.C.Yu(7), A.F.Yuan(5), T.Yuda(9), H.M.Zhang(2), J.L.Zhang(2), N.J.Zhang(6), X.Y.Zhang(6), Y.Zhang(2), Yi Zhang(2), Ying Zhang(7,

2), Zhaxisangzhu(5) and X.X.Zhou(7)

(1)Department of Physics, Hirosaki University, Japan.(2)Key Laboratory of Particle Astrophysics, Institute of High Energy Physics, Chinese Academy of Sciences, China.(3)Institute for Cosmic Ray Research, University of Tokyo, Japan.(4)Department of Physics, Hebei Normal University, China.(5)Department of Mathematics and Physics, Tibet University, China.(6)Department of Physics, Shandong University, China.(7)Institute of Modern Physics, SouthWest Jiaotong University, China.(8)Department of Physics, Yunnan University, China.(9)Faculty of Engineering, Kanagawa University, Japan.(10)Faculty of Education, Utsunomiya University, Japan.(11)Department of Physics, Konan University, Japan.(12)Research Institute for Science and Engineering, Waseda University, Japan.(13)Faculty of Engineering, Yokohama National University, Japan.(14)Department of Physics, Shinshu University, Japan.

(15)National Center for Space Weather, China Meteorological Administration, China.(16)Physics Department and Tsinghua Center for Astrophysics, Tsinghua University, China.(17)Saitama University, Japan.(18)Advanced Media Network Center, Utsunomiya University, Japan.(19)National Institute of Informatics, Japan.(20)Sakushin Gakuin University, Japan.(21)Tokyo Metropolitan College of Industrial Technology, Japan.(22)Max-Planck-Institut fur Physik, Deutschland.(23)College of Industrial Technology, Nihon University, Japan.(24)Shonan Institute of Technology, Japan.(25)RIKEN, Japan.(26)Institute of Disaster Prevention Science and Technology, China.(27)School of General Education, Shinshu University, Japan.(28)Center of Space Science and Application Research, Chinese Academy of Sciences, China.

1. Tibet air shower array.

All-particle spectrum ApJ 678 (2008) 1165

2. Hybrid experiment using AS core detector

to measure proton and helium spectra.

Phys. Lett. B 632 58-64 (2006) & ICRC2007, 2 (2007) 121

3. Compilation of composition measurements.

4. Extra component at the knee and its origin.

5. Next phase experiment.

Contents

Tibet IIIAS array:700 ch x 0.5 m2

scint. detectorswith 7.5m sp.Area 37,000 m2

LocationTibet,

Yangbajing,China

4300 m a.s.l.

606 g/cm2

All particle spectrum.Knee at 4 PeVdJ/dE E∝ -γ γ=2.653.1

ApJ 678 (2008) 1165

Burst detectors

Emulsion Chamber and Burst Detector

2cmArtificial Neural Network

Nγ, ΣEγ, ＜ Rγ ＞ , ＜ ERγ ＞ , Ne , θ

P, He by Tibet ExperimentPhys. Lett. B 632 58-64 (2006)

with 30% model dependence

3.01±0.113.05±0.12

•Ne>3x105

•Zenith angle θ<25 deg.

Number of selected events :1176

during live time of 434.3 days.

•Any 3 PD signals > 100 particles equivalent after the attenuation inside scint. (Nb ～2 x 104 at the center of scinti.)

•Nbtop>5x104, contained events

•632 P,He-like events

Second phase to measure P+He with higher statistics

ICRC2007, 2 (2007) 121

Proton+Helium spectrum

Phase IPhase IPhase II

ICRC2007, 2 (2007) 121

Proton+Helium spectrum

Phase IPhase II

P He

C O

Ne Mg Si S

Ar Ca SubFe Fe

Fit for direct observations

109 1015

Fit for direct observations(<100TeV)

Proton SpectrumDirect measurement and Tibet combined

]1[0

b

EEj

dE

dj

εb : break point (7x1014 eV for proton)Δγ: difference of power index before and after the break point（ Δγ ＝ 0.4 ）

Broken power law formulato describe proton spectrum

Multiple source model

Distribution of acceleration powerof cosmic rays

See Poster 295 (M.Shibata)

εm ≡ εb

Interpretation of εb

Minimum acceleration limit for CR protons.

Threshold of SN explosion by massive stars.

(type II SN by >8M○ ）

CR composition at the kneeεz = Z x εb , Δγ ＝ 0.4

700TeV

CASA/MIA HEGRA KASCADE

DICE BASJE TIBET

All particle spectrum around the knee

1014 1016 1018 1014 1016 1018 1014 1016 1018

1014 1016 1018 1014 1016 1018 1014 1016 1018

All data agree if we apply energy scale correction within 20% by normalizing to direct observations.Extra component can be approximated by

suggesting nearby source(s).Since P and He component do not show the excess at the knee, the extra component should be attributed to heavy element such as Fe.

],PeV4

exp[2 EE

(W.Bednarek and R.J.Protheroe ,2002,APh)

Extra component

P +He spectrum does not show excess at the knee

Expected bymultiple sourcemodel

Chemical composition of SN ejecta

(Nomoto,K et al. Nucl. Phys. A, 621, 467, 1997)

If nearby type Ia SN ejecta makes knee sharp …..

All

He

FeOC+N

CaSi

P

Next phase of Tibet hybrid exp.

YAC:Yangbajing Air shower Core detectorMD:Muon Detector

•Measure the energy spectrum of the main component at the knee.•Detector ： Low threshold BD grid ＋ AS array + Muon detector.•Observe energy flow of AS core within several x 10m from the axis.

2m underground, 20 units, 9000 m2

Water Cherenkov Muon Detector(MD)

Summary•Proton and helium spectra at the knee measured by Tibet hybrid experiment show steep power index of around 3.1 and low fraction to the all particles. Systematic error due to the interaction model dependence is within 30% for the flux.

•Broken power law spectrum is used to summarize the chemical composition measurements based on multiple source model.

• All particle spectrum in wide energy range around the knee shows presence of an extra component which mainly consists of heavy elements and its spectrum suggests the contribution of nearby source(s).

•Next phase of Tibet experiment, Tibet III+YAC+MD, will measure the heavy component at the knee and also measure

γ-ray spectrum with p/γ separation of AS.

Thank you

Pb 7cu

Iron

Scint.

Box

Design of YAC40cm x 50cm, 20x20 channels

S=5000m2

3.75m spacing 400ch Nb>100, any 5　　 (>30GeV)

Wave length shifting fiber+ 2 PMTs (Low gain & High gain)102<Nb<106

All-particle Spectrum in Wide Energy Range (1014-1017eV)

Energy determination : Lateral Distribution Fitting using modified NKG function Derivation of the function was made by detailed detector Monte Carlo (Corsika & EPICS) Carpet array calculation (lateral structure, total size) Sampling array calculation (fit size, resolution)Longitudinal age parameter output by Corsika is used to describe the structure function.

2'/)()'

1()()'

(

)2)()(,2)((21),(

mrsb

mrrsa

mrr

sasbsaBsrf

a(s) b(s)

Modified NKG function

rm’=30 m

S-2S-4.5

For pure electromagnetic cascaderm’ = 80m

a(s) b(s)

Size resolutionby reconstructing MC events

Energy

resolution

~36.0%

(about

150-250TeV)

Energy

resolution

~16.9%

(about

1500-2500 TeV)

Energy

resolution

~11.1%

(about

6×104- 8×104

TeV)

Primary energy resolution

Size spectrum of Tibet III

Generation efficiency of family event by primary protons in QGSJET and SIBYLL

QGSJET

SIBYLL

SIBYLL/QGSJET~1.3SIBYLL/QGSJET

～ 1.3

SIBYLL

QGSJET

SIBYLL

QGSJET

1014 1015 1016

E0 eV 1014 1015 1016

E0 eV

Artificial Neural Network JETNET 3.5

Parameters for training: Nγ, ΣEγ, ＜ Rγ ＞ , ＜ ERγ ＞ , Ne , θ

Primary proton spectrum

Preliminary

(KASCADE data: astro-ph/0312295)

All

ProtonKASCADE (P)

Present Results

(a) ( by QGSJET model) (b) ( by SIBYLL model )

Primary helium spectrum

(a) (by QGSJET model) (b) (by Sibyll model)

p+helium selection: purity=93%, efficiency=70%

J.R.Hoerandel, Astroparticle Phys. 21,241-265(2004)

QGSJET SIBYLL

KASCADE

Fraction of elements (%)

10 eV 10 eV 10 eVProton 22.6 11.0 8.1

He 19.2 11.4 8.4

CNO 21.0 22.6 17.8

NaMgSi 9.0 9.4 8.1

SClAr 5.6 6.2 5.8

Iron 22.2 39.1 51.7

HD model14 15 16

Helium dominant compositionby Kascade e-μmeasurement

Kascade QGSJET spectrum

]exp[6.2

bE

EE

Microsoft 3.0数式

Eb=4 PeV for P

Simulation (Phase I)

Corsika 6.030QGSJET01,SIBYLL2.1 (high energy int. model)

　　　ｘHeavy Dominant Composition (HD)Proton Dominant Composition (PD)

＝ analyses under 4 models

Event Selection

AS size Ne>2 x 105 accompanied by γ family ofEγ>4TeV, 　 nγ 4, ΣEγ>20 TeV

Tibet Hybrid ExperimentTibet 　 Asγ Collaboration

1996 ー 1999 　 AS+EC+BD

　　～ 200 eventsP,He spectrum

Phase2:2002 ー 2005 　 AS+BD

　　 Light component(P+He)

　　　　　 with high statistics>1000 events

Phase3:in preparation 　 AS+BD grid array

　　 Observe heavy component at the knee

Contribution of nuclei with odd Z is corrected using solar abundance

]PeV4

exp[2 EE

The sharpness of the knee suggests limited range of atomic numbers for extra comp

onent

Comparison with chemical composition of Type Ia SNR ejecta

Ca

Expected spectrum of heavy components

Si

S

Fe

Average Mass

GCR+EXGCR(mixed comp.)

GCR only

EXGCR=P

Can CNO constitute extra component?

Akeno

No correction

Normalized at low energy Normalized at high energy

AnisotropyΣρ>1000 （ E0 ＞ 1014 　 eV ）

Orion complex

l=205.5 b=+0.5 Monoceros_Nebula （ α= 99.750 δ=6.500 ）SNR Monoceros is colliding with Rossete nebula.EGRET (98.276 6.764 GEVJ0633+0645)

Initial mass function (IMF)

∝M-2.5

Stellar life time

∝M-1

∝M-3.8

?

Relation between Fermi e± and extra component

at the knee?

PeV nuclei + target（ ＊ 10TeV/n) π0 γ ＊ 100GeV e± This may be quitepossible scinario,but not calculated yet.