1. 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

2. 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

3. 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.

4. 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

5. 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

6. 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.

7. Core position inside circle: R = 450m Zenith angle < 45° 2009-2011 >10 16 eV: 38746 >10 17 eV: 394 m

8. All particle spectra (2009 – 2011) Season 2009-10 Season 2010-11

9. All particle spectra in 2 zenith-angle intervals < 30 º 30º- 45º 5.6 ·10 15 eV

10. Two seasons all particle energy spectrum 400 events with E >10 17 eV

11. 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%

12. “Bump” at 8·10 16 eV ? Fist season spectrum (2009-10) 2 seasons spectrum(2009-11) 4 σ

13. Expanding of effective area: 42 optical detectors at the circle with 1 km radius. Plan for 2011

14. <650 m <750 m <800 m <900 m Without out clusters <450 m

15. Combined spectrum E >10 17 eV 1200 events E>10 18 eV 5 events

16. Power law fitting of combined spectrum

17. All particle energy spectrum KASCADE- Grande – ICRC-2011

20. E = A Q175 0.91 : excellent agreement with KASCADE-Grande

21. 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)

22. 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

23. 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

24. Expanding of effective area <450 m <500 m <650 m <750 m <800 m