Energy Spectrum Measured by the Telescope Array Experiment in 10 ev to 10 ev Range

Transcription

1 Energy Spectrum Measured by the Telescope Array Experiment in 0 ev to 0 ev Range Toshihiro Fujii for the Telescope Array Collaboration KICP, University of Chicago ICRR, University of Tokyo fujii@kicp.uchicago.edu October 6th, 008 Image Credit: Brett Abernethy

2 R.U. Abbasi a, M. Abe b, T. Abu-Zayyad a, M. Allen a, R. Azuma c, E. Barcikowski a, J.W. Belz a, D.R. Bergman a, S.A. Blake a, R. Cady a, M.J. Chae d, B.G. Cheon e, J. Chiba f, M. Chikawa g, W.R. Cho h, T. Fujii i,,, M. Fukushima i,j, T. Goto k, W. Hanlon a, Y. Hayashi k, N. Hayashida l, K. Hibino l, K. Honda m, D. Ikeda i, N. Inoue b, T. Ishii m, R. Ishimori c, H. Ito n, D. Ivanov a, C.C.H. Jui a, K. Kadota o, F. Kakimoto c, O. Kalashev p, K. Kasahara q, H. Kawai r, S. Kawakami k, S. Kawana b, K. Kawata i, E. Kido i, H.B. Kim e, J.H. Kim a, J.H. Kim s, S. Kitamura c, Y. Kitamura c, V. Kuzmin p,, Y.J. Kwon h, J. Lan a, S.I. Lim d, J.P. Lundquist a, K. Machida m, K. Martens j, T. Matsuda u, T. Matsuyama k, J.N. Matthews a, M. Minamino k, Y. Mukai m, I. Myers a, K. Nagasawa b, S. Nagataki n, T. Nakamura w, T. Nonaka i, A. Nozato g, S. Ogio k, J. Ogura c, M. Ohnishi i, H. Ohoka i, K. Oki i, T. Okuda x, M. Ono y, A. Oshima z, S. Ozawa q, I.H. Park aa, M.S. Pshirkov p,ab, D.C. Rodriguez a, G. Rubtsov p, D. Ryu s, H. Sagawa i, N. Sakurai k, L.M. Scott ac, P.D. Shah a, F. Shibata m, T. Shibata i, H. Shimodaira i, B.K. Shin e, H.S. Shin i, J.D. Smith a, P. Sokolsky a, R.W. Springer a, B.T. Stokes a, S.R. Stratton a,ac, T.A. Stroman a, T. Suzawa b, M. Takamura f, M. Takeda i, R. Takeishi i, A. Taketa ad, M. Takita i, Y. Tameda l, H. Tanaka k, K. Tanaka ae, M. Tanaka u, S.B. Thomas a, G.B. Thomson a, P. Tinyakov af,p, I. Tkachev p, H. Tokuno c, T. Tomida ag, S. Troitsky p, Y. Tsunesada k, K. Tsutsumi c, Y. Uchihori ah, S. Udo l, F. Urban af, G. Vasiloff a, T. Wong a, R. Yamane k, H. Yamaoka u, K. Yamazaki ad, J. Yang d, K. Yashiro f, Y. Yoneda k, S. Yoshida r, H. Yoshii ai, R. Zollinger a, Z. Zundel a a High Energy Astrophysics Institute and Department of Physics and Astronomy, University of Utah, Salt Lake City, Utah, USA b The Graduate School of Science and Engineering, Saitama University, Saitama, Saitama, Japan c Graduate School of Science and Engineering, Tokyo Institute of Technology, Meguro, Tokyo, Japan d Department of Physics and Institute for the Early Universe, Ewha Womans University, Seodaaemun-gu, Seoul, Korea e Department of Physics and The Research Institute of Natural Science, Hanyang University, Seongdong-gu, Seoul, Korea f Department of Physics, Tokyo University of Science, Noda, Chiba, Japan g Department of Physics, Kinki University, Higashi Osaka, Osaka, Japan h Department of Physics, Yonsei University, Seodaemun-gu, Seoul, Korea i Institute for Cosmic Ray Research, University of Tokyo, Kashiwa, Chiba, Japan j Kavli Institute for the Physics and Mathematics of the Universe (WPI), Todai Institutes for Advanced Study, the University of Tokyo, Kashiwa, Chiba, Japan k Graduate School of Science, Osaka City University, Osaka, Osaka, Japan l Faculty of Engineering, Kanagawa University, Yokohama, Kanagawa, Japan m Interdisciplinary Graduate School of Medicine and Engineering, University of Yamanashi, Kofu, Yamanashi, Japan n Astrophysical Big Bang Laboratory, RIKEN, Wako, Saitama, Japan o Department of Physics, Tokyo City University, Setagaya-ku, Tokyo, Japan p Institute for Nuclear Research of the Russian Academy of Sciences, Moscow, Russia q Advanced Research Institute for Science and Engineering, Waseda University, Shinjuku-ku, Tokyo, Japan r Department of Physics, Chiba University, Chiba, Chiba, Japan s Department of Physics, School of Natural Sciences, Ulsan National Institute of Science and Technology, UNIST-gil, Ulsan, Korea Japan, USA, Korea, Russia, Belgium s Department of Physics, School of Natural Sciences, Ulsan National Institute of Science and Technology, UNIST-gil, Ulsan, Korea t High Energy Astrophysics Institute and Department of Physics and Astronomy, University of Utah, Salt Lake City, Utah, USA u Institute of Particle and Nuclear Studies, KEK, Tsukuba, Ibaraki, Japan v High Energy Astrophysics Institute and Department of Physics and Astronomy, University of Utah, Salt Lake City, Utah, USA w Faculty of Science, Kochi University, Kochi, Kochi, Japan x Department of Physical Sciences, Ritsumeikan University, Kusatsu, Shiga, Japan y Department of Physics, Kyushu University, Fukuoka, Fukuoka, Japan z Engineering Science Laboratory, Chubu University, Kasugai, Aichi, Japan aa Department of Physics, Sungkyunkwan University, Jang-an-gu, Suwon, Korea ab Sternberg Astronomical Institute, Moscow M.V. Lomonosov State University, Moscow, Russia ac Department of Physics and Astronomy, Rutgers University The State University of New Jersey, Piscataway, New Jersey, USA ad Earthquake Research Institute, University of Tokyo, Bunkyo-ku, Tokyo, Japan ae Graduate School of Information Sciences, Hiroshima City University, Hiroshima, Hiroshima, Japan af Service de Physique Théorique, Université Libre de Bruxelles, Brussels, Belgium ag Department of Computer Science and Engineering, Shinshu University, Nagano, Nagano, Japan ah National Institute of Radiological Science, Chiba, Chiba, Japan ai Department of Physics, Ehime University, Matsuyama, Ehime, Japan address: Now at University of Chicago, USA Deceased

3 Telescope Array Experiment (TA) Largest cosmic ray detector in the Northern hemisphere ~ 700 km at Utah, USA Fluorescence detector + Surface detector array Fluorescence Detector at BRM and LR stations Surface Detector Array ) + 56 Photomultiplier Spherical segment mirror (6.8 m 507 Scintillator,. km spacing tube(pmts)/camera, newly designed telescopes Fluorescence detector at MD station Refurbished from HiRes experiment, Spherical mirror 5. m, 56 PMTs/camera, 4 telescopes 6 6 PMTs PMT 3

4 4 Telescope Array Experiment (TA) Surface detector array (SD) Fluorescence detector (FD)

5 7 Years Steadily Operation Surface detector array (SD) Fluorescence detector (FD) ~00% duty operation Clear moonless night ~0% duty operation Mar 08 Jun 5 Nov 07 Jun 5 5

6 ... to Observe Extensive Air Shower (EAS) induced by Ultra-High Energy Cosmic Ray (UHECR) Image credit: ASPERA_Novapix_L.Bret 6

7 Observed UHECR Event Surface detector array (SD) Fluorescence detector (FD) 43 Observe lateral density distribution Charge density at 800 m, S 800 as energy indicator Observe longitudinal development Reconstruct calorimetric energy Elevation angle [degree] Azimuth angle [degree] Time(µs) Time(µs) 40 #p.e m Number of Photo-Electrons Data Fluorescence 350 Data Direct Cherenkov Fluorescence Rayleigh 300 Scatterd Direct C. Cherenkov Rayleigh Scatterd C. Mie Scattered 50 C. Mie Scattered C. Number of Photo-Electrons Slant Depth (g/cm Slant Depth (g/cm χ /ndf = 35.0/39 (0.7) χ /ndf = 35.0/39 (0.7) ) ) 7

8 nd, denoted by û, and it is bisected by the perpendicular line at the location of the shower core. Energy Estimation by TA SD counter time versus distance from the shower core along the û direction, which is the shower axis on the ground. Points with error bars are counter times, solid curve is the time expected by the fit A look up table made from Monte Carlo simulation Event energy ETBL = function of E TBL is rescaled by the FD ters lying on the û axis, dashed and dotted lines are the fit expectation times for the counters that reconstructed energy to estimate final spondingly.5 and.0 km off the û axis. Right: Lateral distribution profile fit to the AGASA LDF. energy of SD, E SD,final axis is the signal density in Vertical Equivalent Muon (VEM) per square meter units and horizontal e lateral distance from the shower core. VEM is.05 MeV for the TA SD scintillator. E SD,final = E TBL /.7, Y = log 0 [S800 (VEM m - )] χ S800 and zenith angle, sec(θ) / dof ) ] - [ S800 / (VEM m X = Secant of zenith angle A look-up table made from the Monte-Carlo E TBL.5 = f[s800,sec(θ)] 0 log sec θ Z = Color = log 0 (E/eV) log <0% resolution above 0 9 ev (E/eV) (E/eV) 0 TA Hybrid, log /05/-03/05/ TA SD, log (E/eV) 0 8

9 ing on energy; the difference between proton and iron Aperture, Exposure Calculation is at most 6% above 0 7. ev. Our missing energy correction combines the proton and iron results, assuming an energy-dependent proton fraction given by the Detailed Monte Carlo used for aperture calculation in all HiRes/MIA experiment [5] as shown in Figure. The measurement of TA. Exposure = Aperture live-time. uncertainty of the proton fraction was evaluated as 0%. FD aperture needs to assume mass composition. The HiRes/MIA result indicates 50% proton and iron primaries at 0 7 ev, increasing to 90% for energies Use the proton fraction measured by the HiRes/MIA above 0 8 ev. experiment with 0% uncertainty [Astrophys. J. 6 (005) 90]. [ ] 6300 km sr yr TA SD 008/05/-05/05/ 3 0 Proton fraction Proton and Iron model HiRes/MIA 0% uncert. sr] Aperture [km 0 0 Aperture difference on FD Proton Iron HiRes/MIA log (E (ev)) log (E (ev)) 0 9

10 0 Energy Spectrum from TA FD and SD 0 Ankle at loge=8.7±0.0, s - ) Suppression at loge=9.78±0.05 m - (ev 4 /0 3 Flux E sr TA FD TA SD Telescope Array 05 Preliminary log (E (ev)) 0 Item Uncertainty Fluorescence % Atmosphere % Calibration 0% Reconstruction 9% Total %

11 primaries here at 0 7 ev, increasing to 90% for energies above 0 8 ev. γ = exp ( ( 8 ) ) log 0 E b p /p3 8 exp ( ( ) ) (5) 83 log 0 E b p 4 /p5 Proton fraction HiRes/MIA he ratio 0. of the iron and proton best-fit 0% apertures. uncert. The Figure : Proton fraction reported by the HiRes/MIA experiment and its uncertainty [5]. The uncertainty of the proton fraction is indicated 3 by the0dashed line. If the fraction is larger than, purely proton is assumed Quality Cuts Uncertainty attributed above 0to 7. evproton are obtained as shown Fraction in Figure 5. The Assumption nd E b is the energy (in ev) at the break. The best-fit alues are described in Table. The0.8aperture assuming the HiRes/MIA proton fracion, AΩ f, was estimated by the following formula: AΩ f = AΩ P [ R + f ( R) ], (6) here f is the proton fraction and R AΩ Fe /AΩ P is ependence of the aperture on primary species is most 0 vident7 in the7.5 low-energy region, 9but becomes 9.5 0negligi- le at high 0.5 log (E (ev)) 0 energies. sr] Aperture [km 0 0 Proton Iron 86 The geometries of some showers, e.g., those that HiRes/MIA 87 are too- short or faint are difficult to reconstruct accurately. Thus, we apply quality cuts to select only well log (E (ev)) 0 89 reconstructed events in our analysis: the number of hit hours. Analyzing data using the monocular analysis under the same quality cuts, 869 shower candidates log 0 (E (ev)) number of events passing each selection in sequence is summarized in Table. Figure 0: Energy spectrum observed by the BRM and LR fluor Change the proton fraction by the uncertainty of cence detector stations. HiRes/MIA of ±0%, and recalculate aperture of FD. Number of Events s - ) sr - m - (ev 4 /0 3 Flux E Data (Jan/008-Dec/04) Calculated the energy spectrum with those aperture. HiRes/MIA Composition uncert log (E (ev)) Figure 5: Energy distribution of reconstructed showers from seven years of data. 5.. Data/MC Comparison To further ensure the reliability of our analysis, the distributions of several parameters obtained from reconstruction of the observed data are compared with the log (E (ev)) predictions estimated from MC simulations 0using the Proton Iron

12 Comparison with Other Measurements 0 Consistent with the HiRes s - ) sr - result in a broad energy range m - (ev 4 /0 3 Flux E 0 - TA FD TA MD TA SD HiRes-I HiRes-II Auger ICRC log (E (ev)) 0 Consistent with TA MD result 8.5% difference with Auger result around ankle, however consistent within systematics uncertainty.

13 Even if we correct the energy difference, the suppression shows large discrepancy above 09.3 ev. 0 Preliminary Possible reasons of discrepancy: fluorescence yield, atmospheric model, missing energy correction, detector: scintillator or water-tank, Northern/Southern hemisphere. Practical implementation TA 4 : fourfold statistics at the suppression Comparison between the Surface Detectors of the Pierre Auger Observatory and the Telescope Array Water-tank Scintillator on WaterR. Takeishi installed at TA site Tank (AugerPrime) 4.. THE SCINTILLATOR DETECTOR 3 4 Flux E /0 (ev m- sr- s-) Discrepancy on the Suppression TA Combined 05 Auger ICRC % log (E (ev)) CHAPTER 4. THE SURFACE DETECTOR Figure 4.: 3D view of the SSD module with the support bars. The bars are connected to the tank using lifting lugs present in the tank structure Calibration and control system Figure 4.: 3D view of a water-cherenkov detector with a scintillator unit on top. 87 cm R. Takeishi et al, ICRC 05 R, Engel et al, ICRC05 Figure : The two Auger SD stations deployed at the TA Central Laser Facility. The SSD calibration is based on the signal of a minimum ionizing particle going through the The scintillator units have to be precisely calibrated with a technique similar to the caldetector, a MIP. Since this is a thin detector, the MIP will not necessarily be well separated ibration the WCD from the low energy background but, being installed on top procedure of the WCD,of a cross trigger(cf. section 4..7). The size of the detector and its intrinsic accuracy should not be the dominant limitations for the measurement. The can be used to remove all of the background. Aboutmeasurement 40% of the calibration triggers of the 3

14 Further Lower Energy = TALE (Telescope Array Low-energy Extension) Enlarge field of view of FD in elevation to observe lower energy showers down to ev. > ev Fluorescence dominated < ev Cherenkov dominated TALE TA MD TALE TA MD 4

15 5 Resolution and Exposure as a Function of Energy

16 6 Energy Spectrum in ev to ev TALE + TA FD + TA SD Preliminary

17 7 Combined Spectrum and Fitted Result log(e(ev))=6.34±0.04 log(e(ev))=7.30±0.04 log(e(ev))=9.80±0.05 log(e(ev))=8.7±0.0 Preliminary

18 Comparison with other Measurements 8

19 Summary and Future Plans TA measured the energy spectrum over 4.7 orders of magnitude in 0 ev to 0 ev range Large discrepancy with Pierre Auger above ev, which cannot be resolved by rescaling energies of the experiments. TA 4 will provide us fourfold statistics at the suppression. 0 Flux E3/04 (ev m- sr- s-) 4 features seen: low energy ankle at ev, nd knee at 0 ev, ankle at 0 ev, suppression at ev Preliminary TA Combined 05 Auger ICRC % Practical implementation Array 0 Comparison between the Surface Detectors of the8 Pierre Auger Observatory9 and the Telescope R. Takeishi log (E (ev)) 4.. THE SCINTILLATOR DETECTOR CHAPTER 4. THE SURFACE DETECTOR Activities to understand the suppression discrepancy. Figure 4.: 3D view of the SSD module with the support bars. The bars are connected to the tank using lifting lugs present in the tank structure Calibration and control system Figure 4.: 3D view of a water-cherenkov detector with a scintillator unit on top. 87 cm The SSD calibration is based on the signal of a minimum ionizing particle going through the The scintillator units have to be precisely calibrated with a technique similar to the caldetector, a MIP. Since this is a thin detector, the MIP will not necessarily be well separated 9