Knee 領域での空気シャワー実験 研究会「超高エネルギー宇宙線とハドロン 2008 年 4 月 25 日 瀧田 正人 東京大学宇宙線研究所

M.Nagano, A.A.Watson (2000) Cosmic Ray Energy Spectrum

Sommers (ICRC2001)

Experiment siteg/cm 2 eμhC AKENOJapan (35.5N, 138.5E) 930 〇 1 GeV BLANCAUtah (40.2N,112.8W) 870 〇〇 CASA-MIAUtah (40.2N,112.8W) 870 〇 800 MeV DICE860 〇 800 MeV 〇 EAS-TopItaly (42.5N,13.6E) 820 〇 1 GeV HEGRALa Palma (28.8N,17.9W) 790 〇〇 KASCADE (electrons/muons)Germany (49.N, 8.E) 1022 〇 230 MeV KASCADE (hadrons/muons) MeV50 GeV KASCADE (neural network)1022 〇 230 MeV MSU1020 〇 Mt. Norikura Japan735 〇 TibetTibet (30.1N,90.5E) 606 〇 Tunka 〇 Yakutsk (low energy)1020 〇

All particle spectrum Knee around 3-5 PeV ICRC2003 M. Takita

All particle energy spectrum

ICRC2007 Y. Tsunesada (BASJE) Energy dependence of

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 E max ≒ Z * 100 TeV. The position of "knee" must be dependent on electric charge Z

KASCAD E e/  Hadron

Energy Spectrum of Single Elements

Kascade data 2005: different results with different Monte Carlo approaches in data reconstruction. Rigidity scenario not confirmed. Kascade data Kascade data 2003: seem to confirm the rigidity model. BUT

KASCADE : Astroparticle phys. 24 (2005) 1-25

TIBET Yangbajing, Tibet, China 90 ゜ 53E, 30 ゜ 11N, 4,300 m a.s.l. (606g/cm 2 ) BD &EC Air Shower array Phys. Lett. B. 632(2006)58 Tibet-II Air Shower array

Tibet-I to Tibet-II/HD Number of detector I : 45 II : 185 HD: 109 Mode Energy I : 10 TeV II : 10 TeV HD: 3 TeV Area I : 7,650 m 2 II : 37,000 m 2 HD: 5,200 m 2

Characteristics of the Tibet Hybrid Experiment High altitude (4300m a.s.l. 606 g/cm 2 ). Energy determination is made under minimum chemical- composition dependence around the knee. Observe core structure by burst detectors (BD) & emulsion chambers (EC) Select air showers of light-component origin by high energy core detection. (σ ∝ A 2/3 )  Young showers are mostly of proton and helium origins. Air shower axis is known with Δr < 1m.  N e and s are determined precisely. Smaller interaction-model dependence for forward region than backward.

検出方法 宇宙線 空気シャワー シンチレーション光

2 nd particle density 2 nd particle timing Cosmic ray energyCosmic ray direction Air Shower Detection 到着時間 (ns) 粒子数 ~10 TeV

シャワーサイズ Ne の計算（ NKG 関 数） ~3 ｘ eV

Constant fitting o o + Systematic pointing error < 0.01 o Absolute Energy Scale error –4.4% %stat +- 8%sys Energy dependence of Displacements Caused by Geomagnetic field Verification  Absolute energy scale  Pointing error Cosmic Ray Energy Calib. by the Moon’ Shadow by Tibet-III

EC and BD Total EC area : 80 m 2

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 induced 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.

-M.C. Simulation - Hadronic int.model CORSIKA ( Ver ) – QGSJET01– – SIBYLL2.1 – Primary composition model HD (Heavy Dominant) PD (Proton Dominant) HD model 10 14eV 10 15eV 10 16eV Proton He Iron Other PD model 10 14eV 10 15eV 10 16eV Proton He Iron Other 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.

HD modelPD model Primary composition model

Model Dependence of  -family (Generation+Selection) Efficiency in EC QGSJET SIBYLL SIBYLL/QGSJET ~1.3 SIBYLL/QGSJET ～ 1.3 SIBYLL QGSJET SIBYLL QGSJET

Model Dependence of Air Shower Size Accompanied by  -family

Procedures to Obtain Primary Proton Spectrum (  -family selection criteria : Emin=4TeV, Ng=4, sumE >=20TeV, Ne >=2x10 5 ) AS+ECfamily matching eventANN Proton identification (Correlations) (E ,N ,,,sec(θ), Ne ) Int. modelsQGSJETExpt.(80m 2 ) ( ) (699days) SIBYLLExpt.(80m 2 ) ( ) (699days) PrimaryHDPDHDPD Total sampling primary 2x10 8 1x10 8 2x10 8 1x10 8 Number of  -family Selected by ANN (T <=0.4)

Event Matching between EC+BD+AS AS+ECfamily matching event ANN Proton identification (Correlations) (E ,N ,,,sec(θ), Ne ) Measurement Parameter Location(x, y) Time (t) EC (  family) AS BD E ,N ,,,sec(θ) Direction( θ,  ) Y NO Y Y Y NO NO Y Y Ne E0 NbNb

AS&family matching by time coincidence, N burst >10 5 and test 177 ev selected ev expected

Fractions of P, He, M, Fe components (MC) making air showers accompanied by γ-families ModelEnergy(eV)PHeMFe QGSJET+HD ± ±1.200 (%) ± ± ±0.91.6±0.3 SIBYLL+HD ± ±0.800 (%) ± ± ±0.81.6±0.3 QGSJET+PD ±0.88.2±0.800 (%) ± ±0.63.4±0.40.6±0.1 SIBYLL+PD ±0.65.8±0.600 (%) ± ±0.63.4± ±0.01

Selection of proton-induced events by Artificial Neural Network (ANN) （１） sumE （ Total energy EC ） （２） Ng （ number of ganma family EC ） （３） ( mean lateral spread ： ( ～ ( ×H) / EC) （４） （ mean energy flow spread EC ） （５） sec(θ) ( Zenith angle of gamma family EC ） （６） Ne （ Shower size of the tagged air showers AS ）

Selection of proton-induced events with ANN Parameters for training ( sumE, Ng,,, sec(θ), Ne ) Target value for protons=0 others=1 Define threshold value “T th ” Selection efficiency of proton events as a function of “T th ” Efficiency~75% Tth=0.4 Purity~85% Target Value (T)

Comparison of Target Value Distribution. between DATA and MC

Back check: Selection of proton-induced events by ANN

Air shower size spectrum of p-like events vs MC ( for proton like events (ANN out-put <=0.4))

Primary energy estimation ( for proton like events )( 1.0 < sec(theta) <=1.1 )

Back check: Conversion factor for p-like EV ( by QGSJET + HD （ ANN out-put <= 0.4 ) )

Energy resolution

Primary proton spectrum Preliminary (KASCADE data: astro-ph/ ) All Proton KASCADE (P) Present Results (a) ( by QGSJET model) (b) ( by SIBYLL model )

Primary helium spectrum (a) (by QGSJET model)(b) (by SIBYLL model)

Primary ratio Tibet KASCADE (a) (by QGSJET model) (b) ( by SIBYLL model ） All –(P+He) All

733 Scintillators Tibet III AS array + Burst Detector Burst hut 80 m 2 coverage by 100 burst detectors.

Pb 7r.l. Iron 1 cm Scint. 2 cm Box Phase II hybrid experiment Scintillator 50cm x 160cm x 2cm. viewed with 4 PhotoDiodes. Measure size and position of the burst (e.g., e.m. cascade) Electromagnetic component over GeV is responsible for burst size. Scint. was calibrated by accelerator beam.

Proton+Helium spectrum Phase I Phase II

Proton+Helium spectrum Phase I Phase II

Tibet AS (~8.3 万 m 2 ) +MD (384ch, ~10 4 m 2 ) Tibet AS + MD の  点源に対する感度 Tibet AS: Energy and direction of air shower Cosmic ray(P,He,Fe…) Particle density & spread Separation of particles Tibet AS+YAC (1~5 千 m 2 ) 青が期待値 YAC Knee p, He, Fe 100TeV 

Summary ( 1 ) All particle E spectrum -> KASCADE ~= Tibet ( 2 ) Composition KASCADE: small  stat, but large  syst(2~5) x100% Rigidity scenario not confirmed All particle knee bend by light elements Tibet: Large  stat(~10%), but small  syst (~30% for p) The knee of all particle spectrum is composed of nuclei heavier than P + He