Recent results on Ultra-High Energy Cosmic Rays from the Telescope Array
experiment
AMS Days at CERN, Apr. 15-17, 2015
M. Fukushima, ICRR, U-Tokyo
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Calorimetric Measurement of Air Shower
Charged Particles
Fluorescence Air
Surface SD
Detector
Fluorescence Detector
FD
~10 20 eV primary cosmic ray:
Energy, Direction and Particle Species
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Telescope Array (TA)
~700 km 2 by 507 SDs 3 FD stations
Operation: 2008 - Utah, USA
39 o N, 113 o W 1400 m a.s.l.
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• -HV operation and DC coupled
• 12-bit 40 MHz FADC -> 14-bit 10MHz
• Online night-sky BG subtraction
• 5-6 σ signal recognition @ each PMT
• 5 or more adjacent PMTs for trigger
• 30 ms readout dead time per trigger
• ~2 Hz trigger (~7Hz by freq. airplanes)
Fluorescence Detector
FD@MD TALE FD
FD@BRM
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Stereo Camera Images
Stereo Longitudinal Profiles Hybrid Timings
SDs FDs
FD Event Reconstruction (monocular, hybrid, stereo)
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• 12-bit 50 MHz H/L FADC, 16-bit equiv.
• GPS time stamp (~10ns)
• 0.3 MIP 2-fld (top x bottom) wf buff.
-> 700 Hz histo. for gain calibration
• Trigger by 3 MIP, 3 SDs in 8 μs coincidence -> All wf readout by 2.4 GHz radio LAN
• Pipelined (no dead time)
• Average 7 Watt by solar panel + battery
Surface Detector
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SD Event Reconstruction
• S(800m) -> Energy by MC (QGSJET2-03)
• Zenith attenuation by MC (not by CIC)
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SD Energy Rescaling
E SD = E MC-S(800) SD / 1.27
Lo g 10 (E FD /e V)
Log 10 (E SD /eV)
We rescale MC-S(800m) based SD energy by FD energy:
551 Hybrid Events: E SD vs E FD
21% energy scale error
• Telescope Parameters
• Fluorescence Yield
• Atmospheric Attenuation
• Missing Energy
T. Abu-Zayyad et al.
ApP 61(2014)93 9
SD Energy and Angular Resolution
CORSIKA / QGSJET2-03 used
10Energy Spectrum
• 6-year SD spectrum:
E > 10 18.2 eV, θ < 45 o , array border cut
Energy and angular uncert. cut
• Spectrum fit
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18.70
-3.28 -2.67
19.74
G. Thomson, ECRS Sep. 2014, Kiel
6.6 σ off from Cont. Spectrum
-3.3
-2.7
-4.5 10 18.7
10 19.7
SD 6-year Spectrum (E 3 x Diff. Flux)
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SD 5-year Spectrum fitted with extra-Galactic Proton
Cosmic Ray Generation CR Propagation and E-Loss
4-parameter fit Photon Targets:
CMB + IR Interactions:
Photoprod. + Pair Creation
1. X: Energy and 2. Y: Flux 3. Power index: p
4. Cosmological evolution: m Best fit with
p = 2.22, m = 6.3 Δ log E = - 0.05
χ 2 / NDF = 21.3 / 17
V. Berezinsky, A. Gazizov and S. Grigorieva, PRD 74, 043005(2006) TransportCR by O. E. Kalashev and E. Kido, JETP 147 (2015) 917 and
CRPropa by K.-H. Kampert et al., ApP 42 (2013) 41 13
Preliminary:
p = 2.21 +0.10 -0.15 m = 6.7 +1.7 -1.4 Δ log E = - 0.03 ± 0.03 χ 2 /NDF = 12.4 / 17
Allowed Region of (p, m)
~3% sys. err. added in flux.
For CRs originated within z ~ 0.7
P m
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Δlog E=0.2
J.N. Matthews,
Qui Nhon 2014 15
Anisotropy
• E > 10 19 eV, Auger-TA joint analysis
• Correlation of events above cutoff E > 57 EeV (=10 19.76 eV) , θ < 55 o
• Medium scale anisotropy (hotspot)
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A.Aab et al (PAO+TA), ApJ 794:172 (2014)
Anisotropy for E > 10 19 eV (Auger + TA)
Dipole amplitude : 7 – 13%
Quadrupole : 7 – 10%
Equatorial coordinate
99% C.L. upper limit
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P. Tinyakov, 33rdICRC 2013, Rio de Janeiro H. Sagawa, 33rdICRC 2013, Rio de Janeiro
Correlations at E > 57 EeV
Skyplot in Super-Galactic coordinates Auto-correlation
SG Latitude SG Longitude
Probability for isotropic 52 events to create event pairs within
δ –degrees (cumulative)
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Make over-sampling with 20 o radius circle
Sky Plot of SD 5-year Data
• 72 events without array border cut (ΔE/E ~20%, ang. res. ~1.7 o )
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• Chance probability from Isotropic sky is 3.7 x 10 -4 (3.4 σ)
We generated 100k sets of isotropic 72 events, analyzed the same way as the data, and counted how often we have 5.1σ or more enhancement, anywhere in TA’s FoV with any angular size of r=15, 20,… 35
o.We had 37 such sets out of 100k sets in total.
R.U. Abbasi et al., ApJ:790:L21(2014)
Significance Map of Hotspot (r=20 o )
• 19 events found with isotropic BG of 4.5 events (5.1σ by Li-Ma statistics) at R.A.=146.7 o , Dec. = 43.2 o
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+ 1 Year until May 2014
D. Bergman, COSPAR-2014, Moscow G. Thomson, ECRS-2014, Kiel
Red points in the 6
thyear
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A.Aab et al, arXiv:1411.6111v1 K.Kawata, 2014/12/17
TA 6 Years + Auger 10 Years
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K.Kawata, ICRR seminar, 2014/08/27 C.D. Dermer et al., arXiv:0811.1160v3
Nearby Prominent AGNs
TA hotspot: 19 o off from SGP. No obvious source candidate.
Auger warm-spot: Cen A as a source candidate.
Other enhancements may show up with more exposure.
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Composition
• 5-year hybrid: FD @MD x SD good weather
E > 10 18.2 eV θ < 56 o
Xmax in FoV (bracketed)
pattern recognition cuts
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FD/SD Hybrid Reconstruction (Data vs MC)
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Xmax Distribution (Data vs p/Fe MC : QGSJET2-03 )
Log E > 18.2 Log E: 18.2 - 18.4 Log E: 18.4 - 18.6
Log E: 18.6 - 18.8 Log E: 18.8 - 19.0
Log E > 19.0
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R.U.Abbasi et al (TA, ApP 64(2015) 49-62
<Xmax> Ellongation and MC Predictions
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Next Step
TAx4:
• 500 more SDs, 2 more FD stations
• SD: 700 -> 3000 km 2
• Hybrid: x3 acceptance
• Optimized for UHECR above cutoff
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TAx4
H. Sagawa,
UHECR2014, Oct.2014, Springdale 29
Summary
1. For E > 10 18.2 eV, energy spectrum demonstrates clear cutoff and dip.
2. These spectral features are well reproduced by extra-galactic protons (generated with p~2.2, m~6.7)
interacting with the CMB during propagation.
3. Above cutoff (E > 57 EeV ), a strong medium-size anisotropy shows up. The chance prob. is 4.0 σ.
4. From <Xmax>, the composition is proton and/or light nuclei. Not enough statistics for E > 10 19.1 eV.
5. Air shower simulation does not well reproduce, off-core, ground level excess of charged particles:
electrons or muons.
6. The next decade: the study will continue with TAx4 and TALE, in line with Auger-upgrade and K-EUSO.
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