primary cosmic-ray energy spectrum around the knee energy region measured by the tibet hybrid...
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Primary Cosmic-Ray Energy Spectrum Around The Knee Energy Region
Measured By The Tibet Hybrid Experiment
Physics at the End of the Galactic Cosmic Ray Spectrum, Aspen, 26 April, 2005
Masato TakitaICRR, Univ. of TokyoFor The Tibet AS Collaboration
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The Tibet AS Collaboration
M. Amenomori(1), S. Ayabe(2), S.W. Cui(3), Danzengluobu(4),
L.K. Ding(3), X.H. Ding(4), C.F. Feng(5), Z.Y. Feng(6), X.Y. Gao(7), Q.X. Geng(7),
H.W. Guo(4), H.H. He(3), M. He(5), K. Hibino(8), N. Hotta(9), Haibing Hu(4), H.B. Hu(3),
J. Huang(10), Q. Huang(6), H.Y. Jia(6), F. Kajino(11), K. Kasahara(12), Y. Katayose(13), C. Kato(14),
K. Kawata(10), Labaciren(4), G.M. Le(15), J.Y. Li(5), H. Lu(3), S.L. Lu(3), X.R. Meng(4), K. Mizutani(2),
J. Mu(7), K. Munakata(14), A. Nagai(16), H. Nanjo(1), M. Nishizawa(17), M. Ohnishi(10), I. Ohta(9),
H. Onuma(2), T. Ouchi(8), S. Ozawa(10), J.R. Ren(3), T. Saito(18), M. Sakata(11), T. Sasaki(8),
M. Shibata(13), A. Shiomi(10), T. Shirai(8), H. Sugimoto(19), M. Takita(10), Y.H. Tan(3), N. Tateyama(8)
, S. Torii(8), H. Tsuchiya(10), S. Udo(10), T. Utsugi(8), B.S. Wang(3), H. Wang(3), X. Wang(2), Y.G. Wang(5),
H.R. Wu(3), L. Xue(5), Y. Yamamoto(11), C.T. Yan(3), X.C. Yang(7), S. Yasue(14), Z.H. Ye(15),
G.C. Yu(6), A.F. Yuan(4), T. Yuda(10), H.M. Zhang(3), J.L. Zhang(3), N.J. Zhang(5),
X.Y. Zhang(5), Y. Zhang(3), Zhaxisangzhu(4), X.X. Zhou(6)
(1) Dept. of Phys., Hirosaki Univ., Hirosaki, Japan, (2) Dept. of Phys., Saitama Univ., Saitama, Japan,
(3) IHEP, CAS, Beijing, China, (4) Dept. of Math. and Phys., Tibet Univ., Lhasa, China,
(5) Dept. of Phys., Shandong Univ., Jinan, China, (6) Inst. of Modern Phys., SW Jiaotong Univ., Chengdu, China,
(7) Dept. of Phys., Yunnan Univ., Kunming, China, (8) Faculty of Eng., Kanagawa Univ., Yokohama, Japan,
(9) Faculty of Ed., Utsunomiya Univ., Utsunomiya, Japan, (10) ICRR, Univ. of Tokyo, Kashiwa, Japan,
(11) Dept. of Phys., Konan Univ., Kobe, Japan, (12) Faculty of Systems Eng., Shibaura Inst. of Technology, Saitama, Japan,
(13) Dept. of Phys., Yokohama Natl. Univ., Yokohama, Japan, (14) Dept. of Phys., Shinshu Univ., Matsumoto, Japan,
(15) CSSAR, CAS, Beijing, China, (16) Adv. Media Network Center, Utsunomiya Univ., Utsunomiya, Japan,
(17) NII, Tokyo, Japan, (18) Tokyo Metropolitan Coll. of Aeronautical Eng., Tokyo, Japan,
(19) Shonan Inst. of Technology, Fujisawa, Japan
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Outline
i) Research purposeii) Tibet hybrid experimentiii) Monte Carlo simulationiv) Selection of proton-induced events by ANN ( artificial neural network)
v) Results and discussionsiv) Summary
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Research purpose
Thus, measurements of the primary cosmic rays around the "knee" are very important and its composition is a fundamental input for understanding the particle acceleration mechanism that pushes cosmic rays to very high energies.
According to the Fermi
acceleration with supernova
blast waves, the acceleration
limit Emax≒Z * 100 TeV.
The position of "knee"
must be dependent on
electric charge Z
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Features of the hybrid experiment 1) Protons penetrate more deeply into the atmosphere to generate family events due to their smaller inelastic cross sections than other primary nuclei, so that the air shower size and lateral spread of the air shower core induced by protons are smaller than that by those nuclei.
2) Here, a family event is a bundle of high energy particles observed in the air shower core and mostly composed of electromagnetic components generated by a high energy penetrating cosmic ray in the atmosphere.
3) From simulation, we found that among the selected events with (E >= 4TeV, N=4) at Tibet in case of the QGSJET + HD model (SIBYLL + HD), 57.3% (57.5%) are induced by protons, 16.6% (16%) by helium. That is, even if the primary is heavy-enriched, almost half of the observed events selected by the above criteria are induced by protons.
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Tibet Hybrid ExperimentFrom 1996 to 1999, a hybrid experiment consisting of the Emulsion Chamber (EC) and Burst Detector (BD) and Tibet-II Air Shower (AS) array (total area : 36900 m2) was operated at Yangbajing (4300m a.s.l, 606 g/cm2) in Tibet. This experiment can detect a family accompanied by an air shower in the knee region.
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EC and BD Total EC area : 80 m2
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EC and BD
1) A structure of each EC used here is a multilayered sandwich of lead plate and photosensitive x-ray films, photosensitive layers are put every 2 (r.l.) (1 r.l.=0.5cm) of lead in EC.
Total thickness of lead plates is 14 r.l.2) family is mostly cascade products ind
uced by high energy 0 decay - rays which are generated in the nuclear interactions at various depths.
3) It is worthwhile to note that the major behavior of hadronic interactions as well as the primary composition are fairly well reflected on the structure of the family observed with EC.
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-M.C.Simulation-Hadronic int.model
• CORSIKA ( Ver. 6.030 )
– QGSJET01–
– SIBYLL2.1 –
Primary composition model•HD (Heavy Dominant)•PD (Proton Dominant)
HD model
1014eV 1015eV 1016eV
Proton 22.6 11.0 8.1
He 19.2 11.4 8.4
Iron 22.2 39.1 51.7
Other 35.6 38.2 31.7
PD model
1014eV 1015eV 1016eV
Proton 39.0 38.1 37.5
He 20.4 19.4 19.1
Iron 9.4 9.9 10.2
Other 30.4 31.7 33.0
The experimental conditions for detecting family (E >= 4TeV, N=4, E >=20 TeV) events with EC are adequately taken into account. For example, our EC has a roof, namely, the roof simulation and EC simulation are also treated.
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Model Dependence of -family (Generation+Selection) Efficiency in EC
QGSJET
SIBYLL
SIBYLL/QGSJET~1.3SIBYLL/QGSJET
~ 1.3
SIBYLL
QGSJET
SIBYLL
QGSJET
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Model Depndence of Air Shower Size Accompanied by -family
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Procedures to ObtainPrimary Proton Spectrum
( -family selection criteria : Emin=4TeV, Ng=4, sumE >=20TeV, Ne >=2x105 )
AS+ECfamily matching event ANN Proton identification(Correlations)(E,N,< R >,<ER>,sec(θ), Ne )
Int. models QGSJET Expt.(80m2)
(1996-1999)
(699days)
SIBYLL Expt.(80m2)
(1996-1999)
(699days)
Primary HD PD HD PD
Total sampling primary
2x108 1x108 2x108 1x108
Number of -family
5252 7303 177 6801 9655 177
Selected by ANN
(T <=0.4)
3308 4636 111 4312 6192 112
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Event Matching between EC+BD+AS
AS+ECfamily matching event ANN Proton identification(Correlations)(E,N,< R >,<ER>,sec(θ), Ne )
Measurement Parameter
Location(x, y)
Time (t)
EC(family) AS BD
E,N,< R >,<ER>,sec(θ)
Direction(θ, )Y NO Y
Y Y NONO Y NO
Ne E0 Nb
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AS&family matching bytime coincidence, Nburst>105 and test
cm)10(center burst andfamily between Distance:,
deg.) 0.2( AS andfamily between angle Opening:
)()()(
x
2222
y
yx
yx
yx
2
177 ev selected
192 + 14 ev expected
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Selection of proton-induced events by Artificial Neural Network (ANN) (1) sumE ( Total energy EC ) (2) Ng ( number of ganma family EC ) (3) < R > ( mean lateral spread : ( < R > ~ (<PT>×H) / <E>
EC)
(4) <ER> ( mean energy flow spread EC ) (5) sec(θ) ( Zenith angle of gamma family EC ) (6) Ne ( Shower size of the tagged air shower
s AS )
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Selection of proton-induced events
with ANN
Parameters for training( sumE, Ng, < R >, <ER>, sec(θ), Ne )
Target value for protons=0
others=1
Define threshold value “Tth”
Selection efficiency of proton
events as a function of “Tth”
Efficiency~75%
Tth=0.4
Purity~85%
Target Value (T)
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Comparison of Target Value Distribution. between DATA and MC
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Back check: Selection of proton-induced events by ANN
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Primary energy estimation ( for proton like events )( 1.0 < sec(theta)
<=1.1 )
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Back check: Conversion factor for p-like EV ( by QGSJET + HD ( ANN out-put <= 0.4
) )
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Energy resolution
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Air shower size spectrum of p-like events vs MC (for proton like events (ANN out-put <=0.4))
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Primary proton spectrum
Preliminary
(KASCADE data: astro-ph/0312295)
All
ProtonKASCADE (P)
Present Results
( By QGSJET model) ( By SIBYLL model )
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Primary helium spectrum
(a) By QGSGET model (b) By SIBYLL model
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Primary All - (P+He) component
Tibet
KASCADE
(a) By QGSJET model (b) By SIBYLL model
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Summary
PrimaryComposition
InteractionModel = 0.07 < stat.
&( dependence)
( 1 ) Possible steepening of the proton energy spectrum
in the knee region is observed.
power index= ~ -3.1 + ~ 0.15 above 500TeV
cf. Gaisser line (-2.74)
( 2 ) The knee of all particle spectrum is
composed of nuclei heavier than P + He .
( 3 ) The results : Insensitive to Tested Models
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END