the Telescope Array experiment on ultra-high energy cosmic...
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23 April 2018 H. Sagawa ULCA 1
33Recent results of the Telescope Array experiment on
ultra-high energy cosmic rays
Hiroyuki Sagawafor the Telescope Array Collaboration
Institute for Cosmic Ray ResearchThe University of Tokyo
6-July 2018 UNIST seminar H. Sgawa
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INSTITUTE FOR COSMIC RAY RESEARCH(ICRR)
•Director: Prof. Kajita
• Research
• Study on cosmic rays
• Studies with cosmic rays• Cosmic rays in a broad sense
• Astroparticle physics, elementary particles
• Numbers of staffs and students (JFY2017)
• 126 staffs (60 researchers) hired by ICRR
• 65 graduate students 2
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FACILITIES INSIDE JAPAN: 4 OBSERVATORIES
3
UTokyoMain Campus
ICRR
①Super-KamiokandeNeutrino observatoryat Kamioka
②KAGRA (gravitational wave observatory) at Kamioka
③Norikura
④Akeno
XMASS (dark matter)
Kashiwa Campus
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OBSERVATIONAL CORES OUTSIDE JAPAN: 4 SITES
4
④CTA g-ray astronomy
Spain
①Telescope Arrayhighest-energy cosmic rays
USA
③BoliviaHigh Mountain
②Tibet ASg/CR observatoryChina
ICRR
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23 April 2018 H. Sagawa ULCA 5
• Telescope Array (TA)
• Recent results
– Energy Spectrum
– Composition
– Anisotropy
• TA extension
– TAx4
– TALE
Content
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23 April 2018 H. Sagawa ULCA 6
Energy spectrum of cosmic rays
Highest-energy cosmic rays~1020eV
109 1010 1011 1012 1013 1014 1015 1016 1017 1018 1019 1020 1021
Energy (electron volt, eV)
102
10-1
10-4
10-7
10-10
10-13
10-16
10-19
10-22
10-25
10-28
Flux ∝ 𝐸−𝛼
𝛼 = ~3
Cosmic-ray flux
Knee~5×1015 eV
Acceleration of cosmic rays to Knee energy (~5×1015 eV)could be explained by shock wave acceleration(sourc spectral index 𝛼=2.0 ~ 2.2)
at supernova explosions in the Galaxy
What are the most powerful acceleratorsthat generate cosmic rays of 1020 eVin the universe?
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23 April 2018 H. Sagawa ULCA 7
Astrophysical cosmic-ray acceleratorsas source candidates
Hillas condition E < e B r 𝛽
magnetars
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85 nations, 34 institutes, 141 members
USA
Japan
Russia
Belgium
Korea
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Detecting Ultra-High-Energy Cosmic Rays
• To observe particles at the highest energies, the detector must be extremely large.
• The Earth’s atmosphere is used as a detection medium, producing “extensive air showers” from primary Ultra High Energy cosmic rays
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US Light Map
http://i.imgur.com/aOPFB.jpg
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2. Telescope Array (TA)
• TA is located in Millard county (130 miles from Salt Lake City)
• About three times the area of Salt Lake City
• In operation since 2008 11
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Surface Detector (SD)507 plastic scintillator SDs
1.2 km spacing~700 km2
TA detector
12
3 com. towers
39.3°N, 112.9°W~1400 m a.s.l.
Middle Drum(MD)
Black Rock Mesa (BR)
LongRidge(LR)
Need a large flat area• Achievable in the western desert
39.30° N112.91° W1370 m ASL
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Surface Detector (SD)507 plastic scintillator SDs
1.2 km spacing~700 km2
Fluorescence Detector(FD)3 stations
38 telescopes
TA detector
13
3 com. towers
14 telescopes
12 telescopes
12 telescopes
Refurbished HiRes
Middle Drum(MD)
Black Rock Mesa (BR)
LongRidge(LR)
FD and SD: fully operationalsince 2008/May
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23 April 2018 H. Sagawa ULCA 14
Surface Detectors (SD)
2 layers scintillator1.2 cm thick, 3m2 areaOptical fibers to PMTs
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23 April 2018 H. Sagawa ULCA 15
Communication: radio
Power: Solar/Battery
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23 April 2018 H. Sagawa ULCA 16
Long Ridge Black Rock Mesa
Middle Drum
New Telescopes
6.8 m2
~1 m2
14 telescopes @ station256 PMTs/camera
Fluorescence Detectors (FD)
12 telescopes/station256 PMTs/camera
5.2 m2
Reutilized from HiRes-I
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23 April 2018 H. Sagawa ULCA 17
Hybrid event example
SD
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23 April 2018 H. Sagawa ULCA 18
• Telescope Array (TA)
• Latest results
– Energy Spectrum
– Composition
– Anisotropy
• Future of Telescope Array
Content
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23 April 2018 H. Sagawa ULCA 19
TA shower analysis with SD
An SD hit map of a typical event
Time fit
Lateral distribution
profile fit
800 m
S800
Use S800 as an energy estimator
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23 April 2018 H. Sagawa ULCA 20
(SD scaled to FD energy: calorimetric)
E(SD)=ETBL/1.27
E > 1019 eVAngular resolution = 1.4
o
E > 1019 eVEnergy resolution < 20%
Energy Scale Check and Resolution
Hybrid events
Final energy is scaled by 1.27
𝐸𝑇𝐵𝐿
𝐸𝐹𝐷ℎ𝑦𝑏𝑟𝑖𝑑
= 1.27
𝐸𝑇𝐵𝐿 = 𝐸(𝑆800, 𝑠𝑒𝑐𝜃)
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23 April 2018 H. Sagawa ULCA 21
TA SD Spectrum (9 years data)
Log(E/eV) Ankle= 18.69 0.02
Log(E/eV) GZK
=19.81 0.04
Normalized Log Likelihood / NDOF = 21.96/22 N_EXPECT (> GZK, no cut-off) : 79.8N_OBSERVE (data > GZK) : 22GZK CHANCE PROBABILITY : 210-12 ~7BEREZINSKY E_1/2, log10(E/eV) : 19.80 0.05
fit to broken power law
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23 April 2018 H. Sagawa ULCA 22
TA & Auger Spectrum WG report
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23 April 2018 H. Sagawa ULCA 23
Directional exposure of the TA and Auger SDs
7 years of TA SD
12 years of Auger SDs
Declination
TAAuger
Common declination band-15.7° < 𝛿 < 24.8°
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23 April 2018 H. Sagawa ULCA 24
Declination dependence in TA
TA, Auger common declination band-15.7° < 𝛿 < 24.8°
TAAuger
Break points are the same
TA only
North sideSouth side
submitted to ApJ, arXiv:1801.07820
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23 April 2018 H. Sagawa ULCA 25
TA Low-energy Extension (TALE)Galactic to Extra-Galactic Transition
TALE-FD: 10 reused HiRes telescopes to look higher in the sky (31-59o) to see shower development to much lower energies
TALE-SD array: Graded infill surface detector array - more densely-packed surface detectors (lower energy threshold)
TALE-FD: TALE-SD array:
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23 April 2018 H. Sagawa ULCA 26
Nearby Events with Cerenkov
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23 April 2018 H. Sagawa ULCA 27
TALE energy spectrum (monocular)submitted to ApJ, arXiv:1803.01288
Second Knee
Low energy ankle
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23 April 2018 H. Sagawa ULCA 28
Comparison with other measurements
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23 April 2018 H. Sagawa ULCA 29
• Telescope Array (TA)
• Latest results
– Energy Spectrum
– Composition
– Anisotropy
• Future of Telescope Array
Content
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23 April 2018 H. Sagawa ULCA 30
Xmax Technique
Depth [g/cm2]
Nu
mb
er
of
char
ged
par
ticl
e
longitudinal shower development
Xmax
• Longitudinal development of cosmic-ray showers depends on primary particle type
• FD observes longitudinal shower development• Xmax (depth of shower maximum): the most efficient
parameter for determining primary particle type
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Latest Composition: FD Xmax;shower geometry: timing fit including SD
Event Display:SD
Event Display:FD
Timing Geometry Fit (blue points are from SD)
Shower ProfileFit.
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Xmax Distributions vs MCaccepted for ApJ, arXiv:1801.09784
data
Iron
He
N
P
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Xmax Distributions vs MC
Iron
HeN
dataP
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Xmax Distributions vs MC
IronN
HedataP
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<Xmax> vs logE
P
He
data
N
Iron
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Interpretation of <Xmax>?Extrapolation Uncertainties for <Xmax>
Uncertainty at 250 TeV (= 1019.5 eV) encompasses all the models at the ± 1σ level; smaller at 1017 eV.
But the uncertainty is less for RMS(Xmax).
Ulrich, Engel and Unger arXiv:1010.4310v1 [hep-ph] 20 Oct 2010)Thomson and Abbasi, arXiv:1605.05241v1 [hep-ex] 17 May 2016)
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Data/MC: (Xmax) vs <Xmax>
Dots: Resampled MC with same no. of events as data; with contours68.3% (blue), 90% (orange), and 95% (red) confidence intervals
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Data/MC: (Xmax) vs <Xmax>
Dots: Resampled MC with same no. of events as data; with contours68.3% (blue), 90% (orange), and 95% (red) confidence intervals
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Data/MC: (Xmax) vs <Xmax>
Dots: Resampled MC with same no. of events as data; with contours68.3% (blue), 90% (orange), and 95% (red) confidence intervals
Limited Statisticsabove 1019eV!
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Comparing Shifted data to MC
• Likelihood function, 𝐿 (log𝐿 is shown), is constructed for the data against the MC event set (fitted to a Gaussian + exponential tail), vs. shift Xmax in data
• log𝐿 is interpreted as a measured of how much the data resembled the MC
• Max value of log𝐿 is a measured of how much the shifted data resembled MC
H: +29 g/cm2 He: +7 g/cm2
N: --19 g/cm2 Fe: --41 g/cm2
18.2 ≤ log10(E/eV) < 18.3
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Graphing the Results
E<1019.0eV
• max. log𝐿 derived 𝑝 rejects (at 95% C.L.) all species except H
E>1019.2eV
• max. log𝐿 derived 𝑝 FAILS to reject (at 95% C.L.) any species
Color indicates the amount of shift in Xmax applied to data for best fit to MC (in g/cm2)
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23 April 2018 H. Sagawa ULCA 42
• Muon deficit in MC (muon excess in data)
– The number of muons 𝑁𝜇𝑑𝑎𝑡𝑎
measured by Auger ~1.8𝑁𝜇𝑀𝐶
• Water Cherenkov detector
– Sensitive to muon detection
• TA analyzed the lateral distributions of muons
– TA uses scintillator detector• Sensitive to charged particles
– Electromagnetic components
Muon analysis
This is a challenge!
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23 April 2018 H. Sagawa ULCA 43
• 80-90% of TA SD signal derives from electromagnetic components
– Search for the analysis condition on which the muon purity in the SD signal becomes high using MC
– Compare data with MC
• Analysis condition
– Energy: 1018.8 eV < E < 1019.2 eV
– Experimental data: 7 year dataset (2008/May/11~2015/may/11) ~ 3,600 events
– MC: QGSJET II-03 proton, and other models
Method of muon analysis
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23 April 2018 H. Sagawa ULCA 44
• Electromagnetic components generated are attenuated faster than muons in the atmosphere
• By using the SD particles in the air shower to the forward direction, 60-70% of the signal becomes muons
Procedure of muon analysis
ZenithAzimuth
Ave
rage
par
ticl
e d
en
sity
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23 April 2018 H. Sagawa ULCA 45
Result of muon analysis
R(m) R (m)
R (m)
Part
icle
de
nsi
ty
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23 April 2018 H. Sagawa ULCA 46
• Telescope Array (TA)
• Latest results
– Energy Spectrum
– Composition
– Anisotropy
• Future of Telescope Array
Content
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23 April 2018 H. Sagawa ULCA 47
Cosmic rayOrigin
Low energy cosmic rays bend by the magnetic field Isotropy at the Earth
Highest energy cosmic rays Almost go straight against magnetic field Possible to find cosmic-ray hotspot
Why highest energy cosmic rays?
Cosmic rays are charged particles
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23 April 2018 H. Sagawa ULCA 48
• 9 years of TA SD data
• Zenith angle up to 55, loose border cut
• Geometrical acceptance; exposure 8600 km2 yr sr
• Angular resolution: better than 1.5
• Energy resolution: 20%
Anisotropy Analysis
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23 April 2018 H. Sagawa ULCA 49
Global anisotropy Super-Galactic (SG) coordinates
p-value for K-S test = 0.01 for SG latitude, & E > 57 EeV
Isotropic for other energy thresholds/coordinates
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23 April 2018 H. Sagawa ULCA 50
TA Hotspot (5 years data)72 events with E > 57 EeV
Observed: 19Expected : 4.5(26% of events in 6% of area)
Oversampling circle radius: 20o
Maximum pre-trial significance : ~ 5σat RA=146.7o, Dec=+43.2o
Post-trial significance: 3.4σ
Equatorial coordinates
pre-trial significance
Excess
Deficit
ApJL 790:L21, 2014: loose cuts
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Is M82 or Mrk 180 the source?
• M82: starburst galaxy at 3.5 – 3.8 Mpc
• Mrk 180: bright blazar at ~185 Mpc51
H.N. He, A.Kusenko, S.Nagataki, et al., arXiv:1411.5273
Energy or
comment
Hotspot
● > 75 EeVinside
● < 75 EeV
○ > 75 EeVoutside
○ < 75 EeV
E > 57 EeV
Equatorial coordinates
H.Sagawa@JEM-EUSO-JP meeting2018/7/9
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Star Burst Galaxies and highest energy cosmic rays
2018/7/9 H.Sagawa@JEM-EUSO-JP meeting 52
Starburst galaxiesTA and Auger significance
For 20-degree-radius oversampling
(E > 57 EeV using original E scales)
Recently Auger found that the starburst model fits the data better than
the hypothesis of isotropy with a statistical significance of 4.0 sigma,
The highest value of the test statistic being for energies above 39 EeV
TA is checking this hypothesis
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23 April 2018 H. Sagawa ULCA 53
Hotspot with 9 years data
With original 20°oversampling, spot looks larger…. Thus, scan over 15°, 20°, 25°, 30°, & 35°
With 25°oversampling, Maximum pre-trial significance: ~5
at RA=144.3o, Dec=+40.3o
Observed: 34Expected : 13.5
Post-trial significance : 3σ
143 events with E > 57 EeVSGP
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23 April 2018 H. Sagawa ULCA 54
Spectral anisotropy
“cold spot” at lower energies,same place as the hot spot at high
Post-trial significance: 3.7σ
E>1019.2 eV
Maximum pre-trial signif. at (R.A., Decl.) = (139o, 45o)for average spherical cap size <r> of radius 30o
Scanned for log10E > 19.0, 19.1, 19.2, 19.3radius <r> = 15o, 20o, 25o, 30o
7 years of TA SD data
Hot(excess)
Cold(deficit)
red points: events inside the circleblue points: expectation defined
outside the circle
submitted to ApJL, arXiv:1802.05003
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23 April 2018 H. Sagawa ULCA 55
Spectral Anisotropy(from the point of regions with more/less nearby objects)
Super-Galactic Plane (SGP)
Off source region
On source region
log(EON/EeV)= 1.83
log(EOFF /EeV)= 1.67
EON and EOFF: 3.2 difference
Equatorial coordinatesColored dots: 2MRS galaxies (E < 75Mpc)
(within 30o from SGP)
more nearby objects
TA energy distributions(5 years of SD data)
submitted to PRL, arXiv:1707.04967
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23 April 2018 H. Sagawa ULCA 56
• Telescope Array (TA)
• Latest results
– Energy Spectrum
– Composition
– Anisotropy
• Future of Telescope Array
– TAx4
– TALE SD and NICHE
Content
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TAx4• TA
• Surface Det. ( )• 507 SDs (1.2 km spacing), ~700 km2
• Fluorescence Det. ( ): 3 stations
• TAx4 extension• Surface Det. ( )
• Additional 500 SDs (2.08 km spacing)
• Quadruple TA SD (~3,000 km2 incl. TA SD)
• Funded by JSPS from JFY2015 for five years
• Fluorescence Det. ( )• additional 2 FD stations (12 HiRes Telescopes)
• Approved by NSF in 2016
• Northern site construction underway
• Construction from JFY2015
TA
TAx4 ext.
TAx4 ext.
Delta City
57
(JFY: Japanese Fiscal Year)
April – March next year
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23 April 2018 H. Sagawa ULCA 58
① Scintillator counter assembly (Japan)
Utah, USA② Final assembly (workshop)③ Assembled SDs (workshop)④ Staking (for SD positioning and follow-up surveys)
• 2/3 of TAx4 site finished by ATVs• 1/3 will be finished this fall (2017) by helicopter
Plan – Permission from Bureau of Land Management– TAx4 SD deployment
TAx4 SD
12
3
4
Japan Utah, USA
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TALE SD Array
Full TALE SD Array (103) deployed Feb 2017 – now commissioning
2017 March 13 10:23:06
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23 April 2018 H. Sagawa ULCA 60
NICHEUse non-imaging light collection to extend the range of TA/TALE to below 1015 eV- Hybrid with TALE Telescope (left figure)
- 0.25 km2, 70-m spacing (E > 1015.5 eV)- Stand-alone array overlapping with TALE SD
- 1.5 km2, 200-m spacing (E > 1017eV)- 100-m spacing (E down below 1015 eV)
Array of 15 Cerenkov detectors (jNICHE) are being added
jNICHE: funded by JSPS (JFY2014-2017)
March 2017: Deployed 4 Cherenkov Detectors (CDs)
Non-Imaging CHErenkov array
MD/TALE FDsTALE SDsNICHEJ-NICHE
2 CDs TALE
4 jNICHE CDsDeployed in Mar 2017
Triple coincidence
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23 April 2018 H. Sagawa ULCA 61
• TA SD/FD and TALE FD energy spectrum shows spectral features (1015.4 eV < E < over 1020 eV)– ankle (1018.69 eV), cutoff (1019.81 eV)
– 2nd ankle in lower energy region
• TA Xmax: compatible with light composition (E > ~1018.2 eV)
• TA hotspot (3) now appears larger than we originally thought
• TAx4 is coming soon; construction underway
• Full TALE SD was deployed and is coming for stable DAQ.
Conclusions