the telescope array experiment on ultra-high energy cosmic...

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

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

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

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


• Telescope Array (TA)

• Recent results

– Energy Spectrum

– Composition

– Anisotropy

• TA extension

– TAx4

– TALE

Content


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?


Astrophysical cosmic-ray acceleratorsas source candidates

Hillas condition E < e B r 𝛽

magnetars

85 nations, 34 institutes, 141 members

USA

Japan

Russia

Belgium

Korea

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

9

10

US Light Map

http://i.imgur.com/aOPFB.jpg

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

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

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


Surface Detectors (SD)

2 layers scintillator1.2 cm thick, 3m2 areaOptical fibers to PMTs


Communication: radio

Power: Solar/Battery


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


Hybrid event example

SD



• Latest results

– Energy Spectrum

– Composition

– Anisotropy

• Future of Telescope Array

Content


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


(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)


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


TA & Auger Spectrum WG report


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°


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


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:


Nearby Events with Cerenkov


TALE energy spectrum (monocular)submitted to ApJ, arXiv:1803.01288

Second Knee

Low energy ankle


Comparison with other measurements



• Latest results

– Energy Spectrum

– Composition

– Anisotropy


Content


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

31

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.

32

Xmax Distributions vs MCaccepted for ApJ, arXiv:1801.09784

data

Iron

He

N

P

33

Xmax Distributions vs MC

Iron

HeN

dataP

34

Xmax Distributions vs MC

IronN

HedataP

35

<Xmax> vs logE

P

He

data

N

Iron

36

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)

37

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

38



39



Limited Statisticsabove 1019eV!

40

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

41

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)


• 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!


• 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


• 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


Result of muon analysis

R(m) R (m)

R (m)

Part

icle

de

nsi

ty



• Latest results

– Energy Spectrum

– Composition

– Anisotropy


Content


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


• 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


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


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

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

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


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


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


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



• Latest results

– Energy Spectrum

– Composition

– Anisotropy


– TAx4

– TALE SD and NICHE

Content

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


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


TALE SD Array

Full TALE SD Array (103) deployed Feb 2017 – now commissioning

2017 March 13 10:23:06


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


• 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

the telescope array experiment on ultra-high energy cosmic...

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