Recent Results from the Telescope Array Experiment

Heungsu Shin (ICRR, University of Tokyo)
For the Telescope Array Collaboration
20th Lomonosov Conference on Elementary Particle Physics

1Index1. Telescope Array Experiment and TAx4 expansion
2. Energy spectrum results

3. Composition and Hadronic interactions results
4. Anisotropy results
5. Interdisciplinary results

6. Summary2Telescope Array Experiment
Collaboration• 160 Members, 35 Institutes, 7 countries3Telescope Array Experiment
The Largest UHECR Observatory on the Northern Hemisphere• Millard county, Utah, USAMiddle DrumCentral Laser FacilityLong Ridge

Black Rock Mesa
D. Bergman

WikipediaScience Goals• Origin and properties of ultra-high-energy cosmic rays
• High energy hadronic interactions• Multi-messenger studies with photons, neutrino, DM• Interdisciplinary studies with Thunderstorms, TGF, Meteoroids4Telescope Array Experiment
Middle Drum (MD)Surface Detectors••••

507 scintillation detectors
3 m2 detection area
1.2 km spacing~700 km2 coverage

Central Laser Facility

Fluorescence Detectors• 3 stations (BRM, LR, MD)• 12 - 14 telescopes
Black Rock Mesa (BRM)
Long Ridge (LR)5TALE (Low Energy Extension)
Higher elevation FD & Densely deployed SD for lower energy• TALE FD located at MD station (10 telescopes)
Elevation 30° - 57°
TA FD (MD)TALE FDTALE FOVTA FOV• TALE SD array
104 Scintillation detectors (Design identical to TASD)
Various spacing up to 400 m

TALE SD array
6

TA×4
The most recent upgrade of TA
4-fold increase in size of TA SD array• Up to ~3,000 km2• 2 additional FD stations for Hybrid• Observation started since 2019
TA×4 FD (North)

SD deployment7

Spectrum
TA SD 11 years data
(Broken power law fit)Ankle
18.69±0.01

Cutoff19.81±0.03

8Spectrum
TA combined spectrum

2nd knee (26)17.04±0.04(4)16.22±0.02

Cutoff19.81±0.03
Ankle
18.69±0.01

TA SD 11 years data
+ TALE Mono 22 months

9

Spectrum
Instep feature• Pierre Auger reported a spectrum hardening in 1019 eV - 1019.5 eV• Combining TASD, TAFD, Hires data, we observe the Instep feature in the
Northern hemisphere at 1019.25±0.03 eV with 5.3σ significanceTA result

PAO resultParameters
Comparison
10Spectrum
TA + PAO Joint spectrum working group result• Absolute energy scale difference of 9 %• Energy dependent shift ±10 % per decade11Spectrum
Preliminary TA×4 SD spectrum

12

TALE monocular Xmax

13

TALE & TA Hybrid trigger Xmax
Elongation plot : <Xmax>
850
800

TALE Hybrid<Xmax> [g/cm2]

750
700
650
600
550

TA Preliminary
12-23 July 2021
TALE Hybrid
TA Hybrid500

break point : 17.07 ± 0.09
before slope: 25.78 ± 14.52
after slope : 95.13 ± 10.99
χ2/ndf: 0.34 (p = 0.98)

450
400

TA Hybridtrigger

161718logE[eV]Xmax elongation

HiRes/MIA
qgs04 proton, rec.
qgs04 iron, rec.
Xmax Broken Line Fit

1920

4 year dataPreliminary
14

TA SD composition
Machine Learning based on BDT• 16 composition-sensitive observables• 12 years of TASD data

15

TA SD UHE photon limits
New p-γ classifier based on neural network• 16 composition-sensitive observables• Full time-resolved signals from all triggered SD

16

TA p-air cross-section

17

Anisotropy : Dipole
Residual intensity between data and isotropic distribution• Energy threshold E > 8.8 EeV (Corresponding to Auger threshold E > 8 EeV)
• TASD 12 years data

• TA result :𝑟𝛼 ~ 3.1 % 𝛷𝛼 ~ 134°
• Auger result : 𝑟𝛼 ~ 4.7 % 𝛷𝛼 ~ 100°
18

Anisotropy : Hotspot
12 years Hotspot update• Energy threshold E > 57 EeV• Overall post-trial significance from 3.4 σ to 3.2 σ• Growth rate of events inside the hotspot : Consistent with the linear in 1 σFirst 5 yrs
72 events

Last 7 yrs
107 events
19

Anisotropy : Medium scale
Hint of excess in the direction of Perseus-Pisces supercluster• Energy threshold E > 40 EeV20

Terrestrial Gamma-ray Flash
Observation of TGF with TASD
• Broadband interferometer (INTF)
2D high-resolution reconstruction with three 20 - 80 MHz flatplate antennas• Fast Sferic Sensor (FA)
Detects E-field change, Identifies substructure of initial breakdown pulses

21

Thunderstorm
TASD trigger rate variation during thunderstorms• Level-0 trigger rate is monitored at 10 minutes resolution• Result may be interpreted by using EFIELD option of CORSIKA• Trigger rate increase or deficit depends on E-field type of thunderstorm

22

TALE-infill
Ongoing extension plan for TALE for extra low-E sensitivity• Aiming the physics of PeV cosmic ray• 100 m + 200 m spacing covering 0.8 km2

23Summary
1. Energy spectrum measured for 5 decades, 𝟏𝟎𝟏𝟓.𝟓 𝐞𝐕 to 𝟏𝟎𝟐𝟎.𝟓 𝐞𝐕• New feature “Instep” in the energy spectrum at ~𝟏𝟎𝟏𝟗.𝟑 𝐞𝐕• TALE energy spectrum indicated that 2nd knee may be resulted fromPeters cycle
2. TALE Xmax shows composition becoming heavier between knee and 2ndknee
3. TA Hybrid data is compatible with predominantly light elements between
𝟏𝟎𝟏𝟖.𝟎 𝐞𝐕 and 𝟏𝟎𝟏𝟗.𝟏 𝐞𝐕
4. Indications of anisotropy at highest energy• Hotspot from 12 years of data in the direction of Ursa Major (3.2σ)• Hint of excess in the direction of Perseus-Pisces E > 𝟏𝟎𝟏𝟗.𝟑 𝐞𝐕

5. TA×4 started operation and preliminary energy spectrum is measured
6. More expansion plan – TALE infill is ongoing24