The Radio Neutrino
Observatory - Greenland
Detecting ultra-high-energy neutrinos from thenorthern sky
Felix Schlüter - felix.schluter@icecube.wisc.edu

Chiba - 07.08.23

Outline‣
TheRNO-G
detector‣Radio
detectionofUHEneutrinos‣
RNO-G
sciencepotential‣
Deploymentandrecentresults‣
Motivation

Check out our 10 contributions @ the ICRC 2023

2

Ultra-high-energy neutrinos
Not yet discovered!

Astro2020 White Paper, arXiv:1903.04334‣ No measurements above 10 PeV‣ Open questions:- Cuto in astrophysical spectrum- Existence of 2. astrophysicalcomponent- Existence of cosmogenic GZK
neutrino ux➡ Requires IceCube x 10 - 100➡ In-ice radio detectors target

Protons
onlyGZK
Preferred by UHECR datawith 10% protons

energy range: 100 PeV - 10 EeV

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Radio detection of neutrinos
Why?

‣‣ Radio waves are less attenuated in ice
Use natural glacier ice as target

RNO-G, Journal of Glaciology- A single radio station can monitor a cubic
kilometer of ice‣ Radio is a cost e ective solution- In hardware & deployment(do not have to be deployed in3 km depth; 100 - 200 m is su cient)

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Radio detection of neutrinos
Where?

Greenland!

‣Fieldofview(FOV):‣

Existing infrastructure, 10 months of sunlight per year

- Overlapping with IceCube for TeV neutrinos- Complementary with future UHE observatory at South Pole
RNO-G
FOV
@ Summit Station

Equatorial coordinates5Radio Neutrino Observatory - Greenland
What?

‣ 35 stations on 1.25km grid- 7 already deployed & taking data
- 3 - 4 more deployment seasonsare solar powered &‣ Stations
communicate wireless6Station design
A hybrid concept‣ 24 antennas- 3 types- ~ 80 - 650 MHz‣ 3 calibration pulsar
Informedbypilot‣ experiments (ARA &ARIANNA)‣

Will inform IceCubeGen2 radio array design7

Station design
A hybrid concept‣ 24 antennas- 3 types- ~ 80 - 650 MHz‣ 3 calibration pulsar
Informedbypilot‣ experiments (ARA &Shallow component• Upward- &downward-facing
LPDA antennas• CR detection + veto
• Accurate polarisation
reconstruction• Multiple coincidence
threshold trigger

ARIANNA)‣Will inform IceCubeGen2 radio array design7

Station design
A hybrid concept‣ 24 antennas- 3 types- ~ 80 - 650 MHz‣ 3 calibration pulsar
Informedbypilot‣ experiments (ARA &ARIANNA)‣

Will inform IceCubeGen2 radio array design

Shallow component• Upward- &downward-facing
LPDA antennas• CR detection + veto
• Accurate polarisation
reconstruction• Multiple coincidence
threshold trigger
Deep component• 100m deep• “Overlook” larger
volume• Low threshold trigger

7

Station design
A hybrid concept‣ 24 antennas- 3 types- ~ 80 - 650 MHz‣ 3 calibration pulsar
Informedbypilot‣ experiments (ARA &ARIANNA)‣Will inform IceCubeGen2 radio array design

Phased array• Signal of 4 Vpols
combined by phasing
into 8 beams in real
time

Shallow component• Upward- &downward-facing
LPDA antennas• CR detection + veto
• Accurate polarisation
reconstruction• Multiple coincidence
threshold trigger
Deep component• 100m deep• “Overlook” larger
volume• Low threshold trigger

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Antenna sensitivity
3 di erent antenna types‣

LPDA is more sensitive but cannot be deployed in boreholeof Vpol and Hpol gives‣ Combination
polarisation- Hpols is less sensitive because of narrow diameterof borehole- 2 orthogonal LPDAs → Polarisation
LPDAHpolVpol

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Radio detection of neutrinos
How?

Air
Buried in-ice
antennas

Ice

ν

9

Radio detection of neutrinos
How?

Air
Buried in-ice
antennas

Ice

Particle cascade
Emin to detect radio
emission ≳ 1-10 PeVν

9Radio detection of neutrinos
How?

Air
Buried in-ice
antennas

Ice

Particle cascade
Emin to detect radio
emission ≳ 1-10 PeV

νA negative charge-excess
builds up (electrons areknocked out of ice) …
… and produces radio emission (Askaryan 1968)

9

Radio detection of neutrinos
How?
Radio emission pattern has cone
shape due to interference

Air
Buried in-ice
antennas

Ice

Particle cascade
Emin to detect radioemission ≳ 1-10 PeV

νA negative charge-excess
builds up (electrons areknocked out of ice) …
… and produces radio emission (Askaryan 1968)

9

Radio detection of neutrinos
How?
Radio emission pattern has cone
shape due to interference

Air
Buried in-ice
antennas

Ice

Propagation through ice: Bend trajectory due to refractive index of ice

Particle cascade
Emin to detect radio
emission ≳ 1-10 PeV

RNO-G, JINST 16 (2021) 03

νA negative charge-excess
builds up (electrons areknocked out of ice) …
… and produces radio emission (Askaryan 1968)

9

Radio detection of neutrinos
How?
Radio emission pattern has cone
shape due to interference

Air
Buried in-ice
antennas

Ice

Moving of cone reduces signal
strength …

Propagation through ice: Bend trajectory due to refractive index of ice… and higher frequencies vanish
Particle cascade
Emin to detect radio
emission ≳ 1-10 PeV

RNO-G, JINST 16 (2021) 03

νA negative charge-excess
builds up (electrons areknocked out of ice) …
… and produces radio emission (Askaryan 1968)10

Radio detection of neutrinos
How?
Radio emission pattern has cone
shape due to interference

Air
Buried in-ice
antennas

Ice

Moving of cone reduces signal
strength …

Propagation through ice: Bend trajectory due to refractive index of ice… and higher frequencies vanish
Particle cascadeνEmin to detect radioemission ≳ 1-10 PeV

RNO-G, JINST 16 (2021) 03

A negative charge-excess
builds up (electrons areknocked out of ice)
… and produces radio emission (Askaryan 1968)

11

Radio detection of neutrinos
How?

‣ Polarisation of electric eld allows localisation on cone
‣ Several possible ray trajactories
refracted (re ected)
directfifl12

Radio detection of neutrinos
How?

Polarisation of electric eld allows localisation on cone • is produced by >PeV
cascadesSeveral possible ray trajactories• illuminates a spherical(Cherenkov) cone
• gets bend in shallow ice
propagates over km•
refracted (re ected)
distancesdirect• Signal features (frequencyspectrum polarisation)allow to reconstructneutrino properties

fi12fl‣‣The radio emission …

Arrival direction reconstruction
1. Reconstruct vertex position / signal arrival
direction from triangulation

Using cross-correlation to determine signal (time) in each antenna.
Using forward folding technique to determine vertex position /signal arrival direction.
Requires signals in several strings

S. Bouma for IceCube-Gen2, Pos (ICRC23) 1045

I. Plaisier et.al., EPJC 83 (2023) 513

Arrival direction reconstruction
1. Reconstruct vertex position / signal arrival
direction from triangulation
2. Reconstruct viewing angle from frequency
spectrum

Requires strong
signals in Vpols
Using cross-correlation to determine signal (time) in each antenna. on power string
Using forward folding technique to determine vertex position /signal arrival direction.
Requires signals in several strings

S. Bouma for IceCube-Gen2, Pos (ICRC23) 1045

I. Plaisier et.al., EPJC 83 (2023) 513

Arrival direction reconstruction
1. Reconstruct vertex position / signal arrival
direction from triangulation
2. Reconstruct viewing angle from frequencyspectrum
3. Reconstruct polarisation

Requires strong
signals in Vpols
Using cross-correlation to determine signal (time) in each antenna. on power string
Using forward folding technique to determine vertex position /signal arrival direction.
Requires strong
signals in Hpols

Requires signals in several strings

S. Bouma for IceCube-Gen2, Pos (ICRC23) 1045

I. Plaisier et.al., EPJC 83 (2023) 513

Arrival direction reconstruction(for deep antennas only)

S. Bouma for IceCube-Gen2, Pos (ICRC23) 1045

I. Plaisier et.al., EPJC 83 (2023) 514

Energy reconstruction
Viewing angle

Observed Field→ℇ( ) ∝RNO-G, EPJC 82, 147 (2022) RNO-G, JINST 16 (2021) 03−
1exp −2( ( h , ))(1 − )

2

Vertex Distance

Polarization−exp( ( ))→ → →ℓ ×( × ℓ)

1Neutrino energy

True energy𝑓𝐿𝑣
𝜃

𝜃

𝑅

𝑐

𝐸𝑦𝑓

𝜈

𝜈𝑅𝑓

𝐸

𝜎𝑠

Shower energy

15Detecting neutrinos with RNO-G
E ective area
D. García-Fernández et.al., PRD 102 (2020) 8‣

At lower energies: Sensitivity
from electron neutrinos- Strong(er) electromagnetic

cascades in CC interactions

For a (larger)“RNO-G like”
detectorhigher energies: Similar‣ Atsensitivity across all avours- LPM e ect “hurts” radio signal invery high energy em cascades- Muon and tau leptons undergocatastrophic energy losses which
can trigger the radio detector

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Sensitivity
to a di use emission‣ World leading sensitivity @ 1 EeV
Cosmogenic
neutrinosfrom‣ proton interactions with the CMB(GZK cuto )- Not discovered yet- RNO-G will con rm or reject the mostpromising ux expectations‣ Unresolved point source- Extension of astrophysical ux

GZK (protons)

measured by IceCube- Potential to discover a hardening

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ffflff‣ Expect low backgroundM. Muzio for RNO-G, PoS (ICRC23) 1485

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Detecting neutrinos with RNO-G
E ective area
FoV daily variation

aperture just above the‣ Largest
horizonEquatorial coordinates‣ Earth is opaque for UHE neutrinos
in northern hemisphere relevant‣ Observatory
for multi-messenger observation!

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Detecting neutrinos with RNO-G
E ective area
FoV daily variation

aperture just above the‣ Largest
horizonEquatorial coordinates‣ Earth is opaque for UHE neutrinos
in northern hemisphere relevant‣ Observatory
for multi-messenger observation!

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Sensitivity
to transient events‣for multi-messenger‣ Contributor
search also with IceCube-Gen2 in theAble to observe nearby GRBs

southRNO-G, JINST 16 (2021) 03

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Deployment
Drilling 100m deep, 28 cm diameter hole

Shallow antennas are deployed in trenches …

Custom designed driller byBritish Artic Survey (BAS)… which we dig!

Completed stations

Testing wind turbines
for all-year uptime

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Hardware performance
Aka surviving the winter!

Battery charge over the winterData
accumulation

Stable data taking

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First look into the data

Simulated CR
signals

Correlation with template

CRcandidate

Thermal noise

Excess in received power at lower frequencies for
upward-facing LPDAs → Galactic emission

S. Hallmann for RNO-G, Pos (ICRC23) 1043

J. Henrichs and A. Nelles for RNO-G, Pos (ICRC23) 259

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First look into the data
Correlation with solar are

S. Hallmann for RNO-G, Pos (ICRC23) 1043

‣ For 3 solar ares, reconstruct position of Sun
Allowedcorrection/calibration‣ of station geometry

e-Callisto data(International Network ofSolar Radio Spectrometers)

Example t~ 1 degree agreement
RNO-Gantenna

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Summary & Outlook
is currently deploying at Summit Station in‣ RNO-GGreenlandcompleted, RNO-G will have world leading‣ Whensensitivity for 1 EeV neutrinos- Potential to discover the rst UHE neutrino!

will be contributing with UHE neutrino‣ RNO-Gobservation to multi-messenger campaigns in the
Northern Hemispheree orts focus on calibration &‣ Current
commissioning- We have developed reconstruction algorithms- 10 contributions at ICRC23
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‣

We are preparing for neutrino searches!

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Backup26

Calibration
Current e ort!

‣ The ice is part of our detector- Refractive index pro le of crucial
importance➡ See Talk by Bob Oeyen thisafternoon

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Sensitivity to different sources28

Expected number of neutrinos
For di erent ux models

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Several models predictat least one neutrino
when integrating overthe energy

BackgroundAir showers & muons
1. Direct air showeremission

3. In-ice emission if air shower
particles reach ice
Similar signature as neutrinos‣butfrom surface‣

See Uzair Lati this afternoon

erent polarisation‣ Di
pattern, possible veto

2. Huge energy loss fromhigh energy muon
Same signal signature as‣neutrino
but di erent

energy spectrum an arrival
direction distribution

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+ thermal noise & anthropogenic noise

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BackgroundAir showers & muons+ di erences invertex distributionff

L. Pyras et al. PoS (ICRC2023) 1076 + arxiv

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Ice Properties‣ Part of the detector -> needs to be calibrated

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Signals from secondary leptons
Which undergo catastrophic energy losses
For Tau neutrinos

D. García-Fernández et.al.,
PRD 102 (2020) 833

Askaryan Radiation
Speci c polarisation patternfi

34Phased array
For triggering and reconstruction‣ Trigger runs on lower bandwidth (< 250 MHz), 8 beams are formed‣ Design goal for threshold: amplitude_signal / sigma_noise = 2ARA, PRD 105
Techniquedemonstrated
atSouthPolebyARA‣

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Propagation
Signal can reach antennas on di erent trajectories!

Re ectedDirect(+ Refracted)

Double pulse
structure can be usedin reconstruction!

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Solar flare37