1. for the ARA collaboration,
Experimental calibration of the ARA radio neutrino telescope with an electron beam in ice
R. Gaior, A. Ishihara, T. Kuwabara, K. Mase, M. Relich, S. Ueyama, S. Yoshida
for the ARA collaboration,
M. Fukushima, D. Ikeda, J. N. Matthews, H. Sagawa, T. Shibata, B. K. Shin and G. B. Thomson
1st, August, 2015, ICRC2015

2. Askaryan Radio Array (ARA)
Designed to observes high energy neutrinos above 10 PeV using Askaryan radiation
37 stations (3 stations deployed so far)
Each station has 4 strings of 200m depth
Each string has 2 Vpol + 2Hpol broadband antennas (~200–800 MHz)
Total surface area ~100 km2
2 km
K. Mase
1st, August, 2015, ICRC2015
Astroparticle Physics 35 (2012) 457–477

3. The ARA sensitivity ARA37 (3yr)
Test Bed (Tue.): C. Pfendner, １１05, ICRC 2015
ARA2 (Mon.): T. Meures and A. O Murchadha, １１15, ICRC 2015
ARA Test Bed limit
ARA2 limit
ARA37 (3yr)
K. Mase
1st, August, 2015, ICRC2015

4. The ARA calibration with the TA-ELS (ARAcalTA)
Performed in January, 2015 at TA site, Utah
Purpose: Better understanding of the Askaryan signals and the detector calibration
Vpol antenna
Hpol antenna
We measured
Polarization
Angular distribution
Coherence
Bicone ARA antenna
MHz
LNA + filter ( MHz)
Ice target
Antenna tower
Extendable: 2-12m
TA LINAC
40 MeV electron beam line
K. Mase
1st, August, 2015, ICRC2015

5. Ice target and the configurations
100 x 30 x 30 cm3
Easily rotatable structure
Easily movable on a rail
Plastic holder for the ice has a hole underneath for the beam
Thermometer
observation angle
emission angle
ice inclination angle (α)
Dry ice (on side)
1 m
Main data sets
With ice (30°, 45°, 60°)
No target
40 MeV electrons
40 MeV electron beam line
Ice target
Cherenkov angle in ice (56°)
α=30°
α=60°
R. Gaior, 1135,
ICRC2015
K. Mase
1st, August, 2015, ICRC2015
emission angle [deg.]

6. Cover wide range → Coherence
Measured bunch structure
~10 bunches
TA LINAC
40 MeV electron beam
Typical electron number per bunch train: 2×108 → 30 PeV EM shower
Pulse frequency: 2.86 GHz → pulse interval: 350 ps
Bunch train width was optimized to ~2 ns
Beam lateral spread: ~4.5 cm
Trigger signal available
Electron number can be monitored (<1%)
2 ns
Cover wide range → Coherence
2×108 electrons
→ Enough signal strength
Correlation
→ Electron number monitoring
K. Mase
1st, August, 2015, ICRC2015

7. Expected electric field
GEANT4
Bunch structure
Voltage [V]
20 cm ＋
Time [ns]
Distance along the track [m]
E field [V/m] ＋ =
E-filed calculation
(ZHS method)
2 ns
Zas, Halzen, Stanev, PRD 45, 362 (1992)
Time [ps]
K. Mase
1st, August, 2015, ICRC2015

8. Antenna response (T-domain)
Expected waveform
R. Gaior, 1135, ICRC2015
E-field
Antenna response (T-domain)
filter + LNA response
E-field [V/m]
Gain [dB]
2 ns ＋ ＋
Antenna height [m]
Time [ps]
Time [ns]
Frequency [GHz]
Amplitude 60 mV
→ Detectable
Time [s]
Amplitude [V] =
K. Mase
1st, August, 2015, ICRC2015

9. Sudden appearance signal observed by D. Ikeda
Backgrounds
Several backgrounds are expected
Transition radiation
Sudden appearance
Electron Light Source facility
Askaryan radiation
Transition radiation
ice
Transition radiation
Sudden appearance signal
20 cm hole
40 MeV electrons
metal
beam pipe
arXiv:
K. Mase
1st, August, 2015, ICRC2015

10. Comparisons of waveform and the frequency spectrum
Vpol
Simulation (normalized)
Data
Vpol
Simulation (normalized)
Data
x6 for simulation
Configuration:
Ice 30°, obs. angle: 0°
Hpol
Simulation (normalized)
Data
Voltage [V]
The absolute waveform amplitudes are different by 6 times for Vpol
The early part of the waveforms relatively match. There is a difference for the later part
→ Other components than Askaryan radiation
Less Hpol signal → high polarization
x300 for simulation
K. Mase

11. Polarization Time development of polarization
Configuration: Ice 30°, obs. angle 0°, Vpol
Polarization
Data
Simulation
x6 for simulation
Time [ns]
Voltage [V]
Data
Simulation (Askaryan)
Simulation with sys. uncertainty
No target
Data
0.92±0.03
Simulation
1.00±0.01
No target
0.82±0.03
Polarization
Highly polarized
Data
Simulation
Polarization angle
Time [ns]
All signals shows high vertical polarization
Data is off from simulation
K. Mase

12. High coherence, but not full
Time development of coherence
Configuration: Ice 30°, obs. angle 0°, Vpol
Data
Simulation
x6 for simulation
Voltage [V]
Time [ns]
Slope index: 1.86 ± 0.01
Data
Slope index
High coherence, but not full
Time [ns]
High coherence over the main waveform
K. Mase
1st, August, 2015, ICRC2015

13. Electron Light Source facility
Angular distribution
gain, distance corrected
Preliminary
Electron Light Source facility
ice
40 MeV electrons
Observation angle
30 deg.
45 deg.
60 deg.
No target
Solid: Data
Dashed: Simulation
Observed signals are larger than the expected Askaryan radiation
K. Mase
1st, August, 2015, ICRC2015

14. Summary
We have performed an experiment at Utah using the TA-ELS for the better understanding of Askaryan radiation and the calibration of the ARA detectors
Highly polarized and coherent signals were observed
Observed signals are larger than the expected Askaryan radiation
We are going to simulate the background contributions (transition radiation and sudden birth) to explain the difference between data and simulation
K. Mase
1st, August, 2015, ICRC2015

15. Backups
K. Mase
1st, August, 2015, ICRC2015

16. Stability and far field confirmation
The stability with the same configuration: 5% in amplitude
The antenna mast was intentionally rotated by ~15 deg.
The signal amplitude decreased proportionally with the distance change. → Far field confirmation (3.0 ns time delay → 11% distant → 12% amplitude decrease)
Time difference from the expectation was checked for each configuration.
The spread is 1.9 ns → 9° rotation → 6% in amplitude
The overall systematic uncertainty in power: 16%
15 degrees
2015/01/14 Run1
2015/01/14 Run3 (3.0 ns delay corrected)
Configuration:
Ice 60°, obs. angle: 0°, Vpol
K. Mase
1st, August, 2015, ICRC2015

17. Purpose Purpose: Understanding of the Askaryan signals
1962: Askaryan predicted coherent radio radiation from excess negative charge in an EM shower (~20% due to mainly Compton scattering and positron annihilation)
→ Askaryan effect
2000: Saltzberg et al. confirmed the Askaryan radiation experimentally with the SLAC accelerator
P. W. Gorham et al., PRL 99, (2007)
Shower size << λ to be coherent
Purpose: Understanding of the Askaryan signals
Detector calibration
K. Mase
1st, August, 2015, ICRC2015

18. Signals observed
~500 mV
K. Mase
1st, August, 2015, ICRC2015

19. Dependence of the input E-field
R. Gaior
In our case, 0.72
Sensitive to ns input
Upper limit exists
K. Mase
1st, August, 2015, ICRC2015

20. Reproducibility
The reproducibility was checked with data with the same configuration
2015/01/14 Run1 (ice 60 deg., 0m)
2015/01/14 Run4 (ice 60 deg., 0m)
Vpol
Hpol
The difference in the amplitude is 5% → 10% in power (Vol)
K. Mase
1st, August, 2015, ICRC2015

21. Radio wave through Askaryan effect
1962: Askaryan predicted coherent radio emission from excess negative charge in an EM shower (~20% due to mainly Compton scattering and positron annihilation) → Askaryan effect
2000: Attempt to measure Askaryan effect with Argonne Wakefield Accelerator (AWA) (P. W. Gorham et al., PRE 62, 6 (2000))
2001: First experimental detection of Askaryan effect at SLAC with silica sand (D. Saltzberg et al., PRL 86, 13 (2001))
2005: Observation of Askaryan effect in rock salt at SLAC (P. W. Gorham et al., PRD 72, (2005))
2007: Observation of Askaryan effect in ice at SLAC (P. W. Gorham et al., PRL 99, (2007))
We intended to measure the Askaryan radio wave using the Telescope Array (TA) LINAC and use it for end-to-end calibration of the ARA detector
D. Saltzberg et al., PRL 86, 13 (2001)
K. Mase
1st, August, 2015, ICRC2015

22. The ARA system in-ice V-pol antenna H-pol antenna
DAQ at surface
in-ice
DAQ box
optical fiber (~200 m)
~40 dB
V-pol antenna
Bicone
MHz
H-pol antenna
Quad-slot cylinder
MHz
Gain similar to dipole (+2 dBi)
calibrate these detectors
band-pass filter
~40 dB
LNA
Antennas
K. Mase
1st, August, 2015, ICRC2015

23. Askaryan effect → Askaryan effect
G. Askaryan
1962: Askaryan predicted coherent radio emission from excess negative charge in an EM shower (~20% due to mainly Compton scattering and positron annihilation)
→ Askaryan effect
Cherenkov emission (Frank-Tumm result)
in case N electrons,
z=1 (not coherent) → W ∝ N
z=N (coherent) → W ∝ N2
Shower size << λ to be coherent
Power ∝ Δq2, thus prominent at EHE (>~ 10 PeV)
Attenuation length in ice ~ 1 km
K. Mase
1st, August, 2015, ICRC2015

24. optical fiber signal transfer system
Schematic of the ARA system
optical fiber signal transfer system
Antenna
optical fiber (200m)
band-pass filter
DAQ at surface
LNA
DTM
FOAM
in-ice
~40 dB
DAQ box
DTM
FOAM
K. Mase
1st, August, 2015, ICRC2015

25. Antennas V-pol antenna H-pol antenna Bicone Quad-slot cylinder
MHz
H-pol antenna
Quad-slot cylinder
MHz
Gain similar to dipole (+2 dBi)
K. Mase
1st, August, 2015, ICRC2015

26. Parameterization of Askaryan radio wave
J. Alvarez Muniz et al., PRD 62, (2000)
Signal amplitude
J. Alvarez Muniz et al., Physics Lett. B, 411 (1997) 218
Signal spread
56°
Incident particle energy → signal characteristics
Note: confirmed at SLAC
K. Mase
1st, August, 2015, ICRC2015

27. Why radio wave? Radio: ~1km Attenuation length of the south pole ice
Optical: ~100m
Radio: ~1km
Easier to make a bigger detector in an economical way
K. Mase
1st, August, 2015, ICRC2015

28. Antenna calibration
K. Mase
1st, August, 2015, ICRC2015

29. TA LINAC 40 MeV electron beam Maximum electron number per bunch: 109
Pulse frequency: 2.86 GHz → pulse interval: 350 ps
Bunch duration is 20 ns
Output beam width: 7 mm
Trigger signal available
Electron beam
350 ｐｓ
57 bunches
20 ns
T. Shibata et al., NIMA 597 (2008) 61
K. Mase
1st, August, 2015, ICRC2015

30. Antenna transmission coefficient
Top antenna
Antenna transmission coefficient
Measured by network analyzer
Simulation with XFdtd
Measurement consistent with simulation
The difference of top and bottom antenna due to pass-through cables
Bottom antenna
K. Mase
1st, August, 2015, ICRC2015

31. Antenna pattern Same results from two simulations (HFSS and XFdtd)
Measurements are on-going
HFSS
XFdtd
400 MHz
600 MHz
800 MHz
K. Mase
1st, August, 2015, ICRC2015