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Tunka-133: Primary Cosmic Ray Energy Spectrum in the energy range 6·10 15 – 10 18 eV L.A.Kuzmichev (SINP MSU) On behalf on the Tunka Collaboration 32th ICRC, August 15, 2011
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S.F.Beregnev, S.N.Epimakhov, N.N. Kalmykov, N.I.KarpovE.E. Korosteleva, V.A. Kozhin, L.A. Kuzmichev, M.I. Panasyuk, E.G.Popova, V.V. Prosin, A.A. Silaev, A.A. Silaev(ju), A.V. Skurikhin, L.G.Sveshnikova I.V. Yashin, – Skobeltsyn Institute of Nucl. Phys. of Moscow State University, Moscow, Russia; N.M. Budnev, A.V.Diajok, O.A. Chvalaev, O.A. Gress, A.V.Dyachok, E.N.Konstantinov, A.V.Korobchebko, R.R. Mirgazov, L.V. Pan ’ kov, Yu.A. Semeney, A.V. Zagorodnikov – Institute of Applied Phys. of Irkutsk State University, Irkutsk, Russia; B.K. Lubsandorzhiev, B.A. Shaibonov(ju), N.B. Lubsandorzhiev – Institute for Nucl. Res. of Russian Academy of Sciences, Moscow, Russia; V.S. Ptuskin – IZMIRAN, Troitsk, Moscow Region, Russia; Ch. Spiering, R. Wischnewski – DESY-Zeuthen, Zeuthen, Germany; A.Chiavassa – Dip. di Fisica Generale Universita' di Torino and INFN, Torino, Italy. D. Besson, J. Snyder, M. Stockham Department of Physics and Astronomy, University of Kansas, USA Tunka Collaboration
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Tunka-133 – 1 km 2 “dense” EAS Cherenkov light array Energy threshold 10 15 eV Accuracy: core location ~ 6 m energy resolution ~ 15% 133 wide –view optical detectors on 1 sq.km area (PMT EMI 9350 Ø 20 cm) Array description: report ID=495, N.Budnev, this afternoon.
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Energy reconstruction E = A (Q175) g Density of Cherenkov light at core distance 175 m For 10 16 – 10 17 eV g = 0.93±0.02 (CORSIKA) 0.95 for light composition, 0.91 for heavy composition
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Absolute energy calibration : QUEST experiment ( Cherenkov detectors at EAS-TOP) P – steepness of LDF ( Lateral Distribution Function) p Integral spectrum Normalization point for Tunka-133
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Two winter seasons of array operation: 102 moonless nights with good weater. Tunka-133 installed in 2009 - 2009 – 2010: 286 hours of good weather ( November 2009 – March 2010) - 2010 – 2011: 305 hours of good weather (October 2010 – April 2011) > 4 10 6 events with energy 10 15 eV.
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Core position inside circle: R = 450m Zenith angle < 45° 2009-2011 >10 16 eV: 38746 >10 17 eV: 394 m
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All particle spectra (2009 – 2011) Season 2009-10 Season 2010-11
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All particle spectra in 2 zenith-angle intervals < 30 º 30º- 45º 5.6 ·10 15 eV
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Two seasons all particle energy spectrum 400 events with E >10 17 eV
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Power law fitting ±0.05 3power law indexes Systematic errors (0.05) due to uncertainty in g E = A(Q175) g g =0.93±0.02 σ sys (E) = 12%
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“Bump” at 8·10 16 eV ? Fist season spectrum (2009-10) 2 seasons spectrum(2009-11) 4 σ
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Expanding of effective area: 42 optical detectors at the circle with 1 km radius. Plan for 2011
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<650 m <750 m <800 m <900 m Without out clusters <450 m
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Combined spectrum E >10 17 eV 1200 events E>10 18 eV 5 events
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Power law fitting of combined spectrum
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All particle energy spectrum KASCADE- Grande – ICRC-2011
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E = A Q175 0.91 : excellent agreement with KASCADE-Grande
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Next steps 1. Continue data taking for 4-5 seasons. 2. Deployment of 42 distant optical detectors to increase the accuracy of energy reconstruction for the outside events. 3. Deployment of scintillation array for absolute energy calibration at 3·10 16 – 10 17 eV (the new QUEST experiment). 4. Study of air transparency. 5. Deployment of fluorescent detector at 10 km from the array for common operation. (2, 3, 5 – in Budnev report ( ID 495) this afternoon)
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Absolute energy calibration experiment. Repeating the “QUEST” at 10 16 -10 17 eV -20 scintillation counters, 10 m 2 Lg (Ne / E, Tev) p -P -Fe Zenith-angle: 0º -45º Energy: 10 16 – 10 17 eV P – steepness of LDF 2000 events with E >3·10 16 eV per season
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Conclusion 1. The spectrum from 10 16 to 10 18 eV cannot be fitted with single power law index 3.21 ±(0.01)stat ±(0.05)sys ( 6 ·10 15 to 2·10 16 eV.) 2.93 ±(0.01)stat ±(0.05)sys (2 ·10 16 to 10 17 eV.) 3.20 ± (0.06)stat ±(0.05)sys ( 10 17 to 10 18 eV.) 2. Good agreement with KASKADE-Grande and Tibet (up to 7 10 16 ) and GAMMA results (up to 7 10 16 ). 3. A “Bump” at 8.10 16 eV – physics or statistic effect? Not seen in the new 2-years spectrum (2009-11). 4. Next step towards study of the energy spectrum: - far distant optical detectors to increase energy resolution for outside events - scintillation array for absolute energy calibration - study of air transparency - additional MC simulations Thank You
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Expanding of effective area <450 m <500 m <650 m <750 m <800 m
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