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Measurement of the Energy Spectrum by the Telescope Array Surface Detector

Measurement of the Energy Spectrum by the Telescope Array Surface Detector. Dmitri Ivanov Benjamin Stokes Gordon Thomson University of Utah Rutgers University. Telescope Array Collaboration.

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Measurement of the Energy Spectrum by the Telescope Array Surface Detector

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  1. Measurement of the Energy Spectrum by the Telescope Array Surface Detector Dmitri Ivanov Benjamin Stokes Gordon Thomson University of Utah Rutgers University

  2. Telescope Array Collaboration T Abu-Zayyad1, R Aida2, M Allen1, R Azuma3, E Barcikowski1, JW Belz1, T Benno4, DR Bergman1, SA Blake1, O Brusova1, R Cady1, BG Cheon6, J Chiba7, M Chikawa4, EJ Cho6, LS Cho8, WR Cho8, F Cohen9, K Doura4, C Ebeling1, H Fujii10, T Fujii11, T Fukuda3, M Fukushima9,22, D Gorbunov12, W Hanlon1, K Hayashi3, Y Hayashi11, N Hayashida9, K Hibino13, K Hiyama9, K Honda2, G Hughes5, T Iguchi3, D Ikeda9, K Ikuta2, SJJ Innemee5, N Inoue14, T Ishii2, R Ishimori3, D Ivanov5, S Iwamoto2, CCH Jui1, K Kadota15, F Kakimoto3, O Kalashev12, T Kanbe2, H Kang16, K Kasahara17, H Kawai18, S Kawakami11, S Kawana14, E Kido9, BG Kim19, HB Kim6, JH Kim6, JH Kim20, A Kitsugi9, K Kobayashi7, H Koers21, Y Kondo9, V Kuzmin12, YJ Kwon8, JH Lim16, SI Lim19, S Machida3, K Martens22, J Martineau1, T Matsuda10, T Matsuyama11, JN Matthews1, M Minamino11, K Miyata7, H Miyauchi11, Y Murano3, T Nakamura23, SW Nam19, T Nonaka9, S Ogio11, M Ohnishi9, H Ohoka9, T Okuda11, A Oshima11, S Ozawa17, IH Park19, D Rodriguez1, SY Roh20, G Rubtsov12, D Ryu20, H Sagawa9, N Sakurai9, LM Scott5, PD Shah1, T Shibata9, H Shimodaira9, BK Shin6, JD Smith1, P Sokolsky1, TJ Sonley1, RW Springer1, BT Stokes1, TA Stroman1, SR Stratton5, S Suzuki10, Y Takahashi9, M Takeda9, A Taketa9, M Takita9, Y Tameda3, H Tanaka11, K Tanaka24, M Tanaka10, JR Thomas1, SB Thomas1, GB Thomson1, P Tinyakov12,21, I Tkachev12, H Tokuno9, T Tomida2, R Torii9, S Troitsky12, Y Tsunesada3, Y Tsuyuguchi2, Y Uchihori25, S Udo13, H Ukai2, B Van Klaveren1, Y Wada14, M Wood1, T Yamakawa9, Y Yamakawa9, H Yamaoka10, J Yang19, S Yoshida18, H Yoshii26, Z Zundel1 1University of Utah, 2University of Yamanashi, 3Tokyo Institute of Technology, 4Kinki University, 5Rutgers University, 6Hanyang University, 7Tokyo University of Science, 8Yonsei University, 9Institute for Cosmic Ray Research, University of Tokyo, 10Institute of Particle and Nuclear Studies, KEK, 11Osaka City University, 12Institute for Nuclear Research of the Russian Academy of Sciences, 13Kanagawa University, 14Saitama University, 15Tokyo City University, 16Pusan National University, 17Waseda University, 18Chiba University 19Ewha Womans University, 20Chungnam National University, 21University Libre de Bruxelles, 22University of Tokyo, 23Kochi University, 24Hiroshima City University, 25National Institute of Radiological Science, Japan, 26Ehime University

  3. Outline • Surface detector configuration • Simulation program • Dethinning • Spectral event set generation • Event reconstruction • Validation • Energy spectrum estimation

  4. Telescope Array Surface Detector Configuration • Located 200 km SW of Salt Lake City • 507 surface units on 1.2 km rectangular grid • Total area: 680 km2 • SD augmented by 3 air fluorescence stations • SD commissioned in May 2008

  5. Event Reconstruction Time Fit (Geometry) (S800) LDF Fit Each counter self-calibrates every 10 min

  6. A Careful Analysis Method • No CIC approach, but rather full Monte Carlo • Simulate the data the same way it is observed by writing out the MC events in same format as data. • Fits tuned to data using functional form observed by previous experiment (i.e. AGASA) to ensure model independence. • Analyze the MC with the same programs used for data. • Confirm with data/MC comparison plots.

  7. Simulation Program • CORSIKA 6.960 • QGSJET-II/FLUKA • New Techniques • Parallelization • Dethinning • CORSIKA itself left untouched • GEANT4 • Superb detail • Very computationally intensive • See Poster 1288 for a more detailed description (August 16-17, Poster Room 2, #55)

  8. Simulation Program:Augmentations to CORSIKA • Parallelization • Wrapper scripts and binaries • CORSIKA itself left untouched • 100+ showers • 1018.5 to 1019.5 eV • 0o to 60o zenith • p, Fe

  9. Simulation Program:Augmentations to CORSIKA • Dethinning • Change each CORSIKA output particle of weight w to w particles with similar characteristics to the original particle • Adjust dethinning parameters to agree with full CORSIKA generated via parallelization

  10. Verifying Dethinning:Lateral Profile Proton, 1019 eV, 30o zenith angle Dethinned 10-6 thinning VEM / Counter RMS Mean Dethinned Non-thinned Thinned Non-thinned Distance from Core, [km]

  11. Verifying Dethinning:Temporal Distribution 10-6 Thinning Non-thinned Dethinned Non-thinned 800m 1400m Lateral Distance 2000m t50 (msec normal to shower front)

  12. Simulation Program:Reproducing the Real Data Set • CORSIKA shower library: • 13,800 dethinned showers • 1017.1 to 1020.5 eV • Isotropic distribution • Calculate energy deposition for entire shower • GEANT4 • Simulate SD electronics with real time calibration info. • Select events for data set with respect to previously measured energy spectrum

  13. SD Analysis:Fitting Residuals • Residuals are computed over entire data set and inputed into histogram • Once AGASA fitting functions are shown to work for data, the process is repeated for MC set • Monte Carlo fits the exact same way as the real data • Consistent for both geometric and lateral density fits. Time fit residual over σ DATA MC Counter signal, [VEM/m2]

  14. SD Analysis:Geometric Data/MC Comparisons Zenith angle Azimuth angle

  15. SD Analysis:Geometric Data/MC Comparisons Core Position (E-W) Core Position (N-S)

  16. SD AnalysisAngular Resolution 1.5º 2.1º E > 1018.5 eV E < 1019 eV E > 1019 eV 2.5º E < 1018.5 eV

  17. SD Analysis:Energy Determination • Energy determination table is constructed from the fitting results of the Monte Carlo. • First estimation of the event energy is done by interpolating between S800 vs. secθ isoclines. log10S800 secq

  18. SD Analysis:Energy Scale • SD and FD energy estimation disagree • FD estimate possesses less model-dependence • Set SD energy scale to FD energy scale using well-reconstructed events from all 3 FD detectors • 27% renormalization.

  19. SD Analysis:LDF Data/MC Comparisons S800 Energy

  20. SD Analysis:Energy Resolution

  21. SD AnalysisAperture and Exposure • For E>1018.8 eV: • Aperture • 900 km2 sr • Exposure • 2700 km2 sryr • Calculation convolves data resolution and quality cuts Aperture Exposure

  22. SD Energy Spectrum:Broken Power Law Fit 3 years data, 10,997 events

  23. SD Energy Spectrum:GZK Feature

  24. SD Energy Spectrum:Integral Flux E1/2 Measurement E1/2 = 1019.69 eV Berezinsky et al. predict 1019.72 eV

  25. SD Energy Spectrum:Comparison ● TA SD □ TA MD

  26. SD Energy Spectrum:Comparison ● TA SD ▲ HiRes-I ▼ HiRes-II

  27. SD Energy Spectrum:Comparison ● TA SD ■ Auger 2008 (PRL) +20% ▲ Auger 2011 (ICRC) +20%

  28. Conclusions • TA possesses the largest aperture for UHECRs in the Northern Hemisphere. • We developed new techniques for SD analysis • We normalized the SD energy scale to all three fluorescence detectors • The spectrum shows the ankle and the GZK cutoff

  29. Acknowledgments

  30. SD Energy Spectrum:Comparison ● TA SD □ AGASA -25%

  31. Update to Stanev-Gaisser Compilation

  32. SD Analysis:Data Quality Cuts • Functional fit quality: • c2/d.o.f.: > 4.0 • Pointing direction resolution: < 5o • Fractional S800 uncertainty: < 25% • Shower geometry quality: • Border Cut > 1200m • Zenith Angle Cut: < 45o

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