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Radio Detection of Astrophysical Neutrinos Towards finding the sources of UHECRs Anna Nelles
Scientific motivation Where are ultra-high energy cosmic rays from? Does the neutrino flux continue to higher energies? Nelles, Seminar Oxford, 2021 (virtual) 2
Radio emission of showers
The story of the two effects and the refractive index
• Radio emission of showers can be explained from first principles and three aspects
• Magnetic field: Geomagnetic field, Lorentz-force
• Charge imbalance: Particle Physics processes
• Index of refraction: Relativistic compression
+
+
+
+
— +
— + — —
— + — —
Nelles, Seminar Oxford, 2021 (virtual) 3
Radio emission of showers
How do we know this?
• The key evidence: Polarization
• Geomagnetic effect: Lorentz-force,
polarization orthogonal to shower axis
and magnetic field
• Askaryan effect: Polarization points
towards shower axis
30 - 80 MHz LOFAR (AN), JCAP 10 (2014) 014
Nelles, Seminar Oxford, 2021 (virtual) 4
Radio emission
FIG. 2: The ofparameters
set of normalized Stokes showers that characterize the polarization footprint of a single air shower.
Refer to the caption of Fig. 1 for the meaning of the symbols.
How do we know this?
in the data points, reflecting the layout of the antenna LOFAR (AN) , Phys. Rev. D.94.103010
• Thestations.
key evidence: Polarization
The angular dependence of the circular polarization is
The
• most twoseen
clearly processes stem
in Fig. 3 where from of the
the footprint
Stokes parameter V is shown as obtained from the simu-
slightly
lation and data.different heights
As expected, see Eq. (3), ê~v⇥B~ is the axis
of anti-symmetry, where V changes sign along ê~v⇥~v⇥B~ to
• -ê~vTime
⇥~
v ⇥B~ . difference = phase offset
In analyzing the accumulated data from LOFAR we
between
concentrate on atwo emission
distance of 100 m from the shower axis
components
since this is close to the distance where Cherenkov ef-
fects (relativistic time compression) are large and thus
the pulse will have a flat frequency spectrum within our
Leadswindow.
• observing to circular polarization
From the maximum values at 100 m,
as can be read from Fig. 2, where = ±90 , one obtains
V /U ⇡ 1/3 giving ⌘ ⇡ 0.3 using Eq. (3).
In Fig. 4 the measured values for U/I and V /I are
given for all antennas at a distance between 90 and 110 m FIG. 3: The footprint of the value of the Stokes
• fromEmission
the core for is the
due 114to both geomagnetic
high-quality events measured emission
background
(dominant
V -parameter
color shows the
in
for a measured air) and
air shower.
results of the
The
CoREAS
at LOFAR as given in Ref. [6]. To restrict the analysis
toAskaryan
antennas at anemission
angle close to 90 with respect to the simulation while the coloring in the small circles
~v ⇥ B ~ axis, the additional condition | cos | < 0.5 was presents the data. This is the same data as shown in
Fig. 2 (right most panel), however not normalized by I
Geosynchrotron
• imposed. A quality cut is radiation
applied whereis onlya those
correction
data ofbut< by
1% to these effects
the maximum of V. At close distances the
are retained for which the measurement error in both
U/I and V /I is smaller than 10%. This leaves us with 106 predicted values for V su↵er from numerical instability
antenna readings. The average of the data given in Fig. 4 in the simulation.
is V /U = 0.32 giving ⌘ ⇡ 0.31 with a considerable spread
as can be seen from the figure. This value supports the
result derived from the single event shown in Fig. 2. The
Stokes parameters are measured in the frequency band
Nelles, Seminar Oxford, 2021 (virtual) 5
30-80 MHz. Taking the central frequency as reference
Radio emission of showers
There is also a Cherenkov ring but not Cherenkov emission
• The emission is only strong if it A.Nelles et al. (LOFAR)
Astropart Phys, 65, 2015, 11-21
arrives coherently (at the same time 110 - 190 MHz
for all frequencies, high frequencies
more pronounced effect)
• At the Cherenkov angle, an
enhancement is seen, in air this is
very close to the shower axis
• Same effect for showers in ice, but
here Cherekov angle ~ 52 degrees,
so it looks much more like
“Cherenkov radiation”, but it is not High-Band Antennas
• If one had the same shower
development in vacuum, it would still
radiate
Nelles, Seminar Oxford, 2021 (virtual) 6
We know all this from air showers
Are air showers still interesting?
• Air shower measurements were used to:
• Provide the proof-of-principle for radio detection of particle showers
• Confirm the emission mechanisms down to subtle features, agreement with
Monte Carlo simulations astonishingly good
• Develop methods of how to reconstruct data, remove the contribution of
noise, understand antenna theory for impulsive events, …
• But a technique is only useful, if it can also contribute to advancing the
astroparticle science case
e c trum er ph ysics
rg y
sp Air show ics
ne Particle Phys
c-ray e
o s mi
C Acceler Sources
Cosmic ation of UHE
-ray com CR
position
tion
Propaga
Nelles, Seminar Oxford, 2021 (virtual) 7
Detecting radio emission of air showers
What is in it for the science?
6
A. Aab et al. (AN), PRL 116 (2016) 24, 241101
A · 107eV( ECR /1018eV) B , A = 1.58 ± 0.07, B = 1.98 ± 0.04
• Radio detection provides and
109 3 - 4 stations with signal excellent energy estimator
5 stations with signal
• Calculation from first principles
108 • Very little systematic uncertainties
[eV]
(< 5%) in method
2
80 MHz / sin
M. Gottowik et al. Astropart. Phys. 103 (2018) 87
107 Simulations only
Auger
E 30
106
AERA vs Auger SD
105 17
10 1018 1019
ECR [eV]
Nelles, Seminar Oxford, 2021 (virtual) 8
FIG. 2. Correlation between the normalized radiation energy
Detecting radio emission of air showers
What is in it for the science?
• Negligible corrections due to K.Mulrey et al. (AN) JCAP 2020 017
atmospheric effects on energy-scale
• Auger has so far shown the most
thorough detector calibration,
obtaining an absolute scale
uncertainty of 14 %
• A radio energy estimate could
reduce systematic uncertainties
between observatories with
modest experimental efforts
• First try: LOFAR vs. Auger,
comparing Auger Surface Detector
to LORA scintillator array at LOFAR:
ECRLORA/ECRAuger= 1.06±0.20
Figure 4. Relation between the corrected radiation energy measured by the LOFAR antennas an
Nelles, Seminar Oxford, 2021 (virtual) cosmic-ray energy as determined by the LORA scintillators. The error bars represent event-by-e
9
uncertainties. The purple line shows the best fit line for LOFAR measurements of corrected radi
Detecting radio emission of air showers
What is in it for the science?
• Radio pattern is very sensitive to Xmax
• LOFAR has presented high precisions Xmax
measurements, σXmax= 17 g/cm2
distance to Xmax
A. Corstanje et al, Update to Nature 2016
About to be submitted to PRD
footprint width footprint width
• Slight tension to Auger FD
measurements, but agreement
with other Northern hemisphere
experiments
Johannes Schulz
• Eagerly awaiting Auger RD/FD
hybrid study
Nelles, Seminar Oxford, 2021 (virtual) 10Detecting radio emission of air showers
The global neighborhood
• Multitude of air Figure: Huege 2016
shower arrays
• Many of the in hybrid
configuration, tuned
at different purposes
• Square-kilometre
array (SKA) very
different
• Not shown: Auger
upgrade contains
radio antennas at all
Surface Detector
Stations: Radio a
‘standard' tool planned
+neutrino detectors in ice
ARIANNA, ARA, IceTop, ..
+ANITA balloon
Nelles, Seminar Oxford, 2021 (virtual) 11Ideas for the Square Kilometre Array
Taking radio emission to the next level of detail
LOFAR (Old configuration) SKA-low
• LOFAR typically detected air showers with ~500 antennas, SKA will provide a
multitude of antennas with better frequency coverage 50 - 350 MHz
• Radio emission contains information about the whole shower development,
more than shower maximum
• Relevant both for particle physics and air shower physics
Nelles, Seminar Oxford, 2021 (virtual) 12Ideas for the Square Kilometre Array
Taking radio emission to the next level of detail
• With sparse arrays, one has to interpolate air
shower footprint or fit a lateral distribution
function, which induces uncertainties Simulations: Arthur Corstanje
• SKA has enough antennas to use the raw data
directly
• Next to height of shower maximum may be able
to resolve height of first interaction, shape of
shower, ‘clumpiness’, etc
• = More precise access to cosmic ray
composition
• = Independent handle on hadronic interaction
models
• Currently all methods work in progress, some
ideas a bit speculative, …
Nelles, Seminar Oxford, 2021 (virtual) 13Short digression:
You never know what is coming
• When working on the air shower
detection with LOFAR, we
realised:
• Thunderstorms influence air
showers and their radio emission
• See e.g. Trinh et al, JGR: Atmospheres 125 (8)
31433, Schellart et al, PRL 114 (16) id.165001
• LOFAR is the world’s most
powerful lightning interferometer Nelles, Hare (2019)
• See e.g.: Hare et al. Nature 568 (7752), 360-363,
PRL 124 (10), 105101, JGR: Atmospheres 123 (5),
2861-2876
• As astroparticle physicists we are
contributing to leading questions
in atmospheric research
Nelles, Seminar Oxford, 2021 (virtual) 14Detecting radio emission of air showers
Experimental challenges and opportunities
Jelley et al, Nature 1965
• Search for a very broad-band
nanosecond scale pulse
• Detectable typically at shower
energies > 1015 eV, i.e. rare signal
• Sampling speeds of at least 200 MHz
• Needs full waveform sampling for
frequency content and polarization 40 - 48 MHz
• Preferably stations run independently
at very low power Jelley et al Nature 1965, R. A. Porter MSc Thesis 1967,
• Duty-cycle (almost) independent of
weather
10 - 90 MHz
Nelles, Seminar Oxford, 2021 (virtual) 15Detecting radio emission of air showers
Experimental challenges and opportunities
ARIANNA Coll. (AN)., Astropart. Phys. 90 (2017) 50
• Unfortunately, a lot of things
make radio pulses
NO cosmic ray cosmic ray
• Self-triggering and event
identification remain a challenge
• Site quality important
• New opportunities in modern
Nelles, Seminar Oxford, 2021 (virtual)
data analysis methods 16Radio emission of showers in dense media
A difference between detecting cosmic rays and neutrinos
arXiv:2010.12279
• Showers in media are smaller,
i.e. more intense charge
imbalance and less influence of
geomagnetic field
• Higher frequencies due to
smaller size
• Index of refraction >> 1,
Cherenkov cone, travel on non-
straight lines with changing n
• Ice attenuates the signal, air
does not
Nelles, Seminar Oxford, 2021 (virtual) 17Radio detection of neutrinos
Why it is interesting for neutrinos?
• Any shower containing
an electro-magnetic
cascade creates radio
emission
• A similar experimental
approach for:
• air showers from
cosmic rays
• air showers from
neutrino induces tau
ARIANNA collaboration
decays
• in ice showers
following a neutrino • All experiments utilize negligible radio
interaction attenuation in air and kilometer-scale
attenuation length in ice
Nelles, Seminar Oxford, 2021 (virtual) 18Radio detection of neutrinos
Neutrino interactions in ice
• Cold polar ice has attenuation length in the order of kilometers
• One radio station can typically monitor 1 km3 of ice (= the size of IceCube)
• Detection threshold around 10 PeV shower energy, determined not by array
spacing but pulse height above thermal noise
• > 100 km3 needed to obtain sensitivity for cosmogenic neutrinos, neutrinos from
UHECR with CMB, if very few protons at highest energies
• Human-made background typically smaller in
polar regions, event identification and
self-trigger less challenging
• Many early experiments:
RICE, ARA, ARIANNA, … and of course, ANITA
ν e,μ,τ
Nelles, Seminar Oxford, 2021 (virtual) 19Radio detection of neutrinos
Results so far ANITA-II
• Neutrino limits from radio detection
of neutrinos towards high energies,
not competitive to IceCube
below 1010 GeV
• So far: experiments focussed on
proof-of-concept,
reconstruction and performance
• Exception: ANITA I-III: Mystery events — behave like cosmic ray signals, but
show signal polarization/polarity like neutrino from deep trough Earth
• If truly neutrino: disagreement with IceCube limits, difficult to reconcile with
Standard Model
• Other explanations offered: ice, background, etc.
• ANITA IV: again 4 events with inconsistent polarity, but near horizon,
nothing ‘mysteriously’ steep arXiv:2008.05690
Nelles, Seminar Oxford, 2021 (virtual) 20Radio detection of neutrinos
PUEO: The Payload for Ultrahigh Energy Observations
• Much lower threshold than ANITA (x10
more sensitive across energies), takes over
from IceCube at 1018 eV
• Especially large instantaneous effective
Whitepaper:
volume, for transient, point source, and arXiv:2010.02892
multi-messenger searches
• Order-of-magnitude improvement enabled
by:
• interferometric phased array trigger
• real-time digital filtering
• x2 more antenna collecting area above
300 MHz
• Improved pointing resolution
Selected for Pioneers Mission by NASA
Scheduled to fly in December 2024
Nelles, Seminar Oxford, 2021 (virtual) 210 10 km
Radio detection of neutrinos
Where will it go next? N RNO
-G a
e
rray
ers
trav
• RNO-G: Start construction in 2021
Sat
drill site ay
iw
Ice
k
• 35 stations as first production scale re
ho
le
s
bo
implementation for neutrino detection
C
IS
D
Station
Clean air/snow sectors
• Deployment in Greenland allows for fast
development turn-around
• Europe-led experiment with
members from all previous
in-ice experiments
• Largest yearly neutrino
sensitivity > 10 PeV
• Concept and design paper:
Accept at JINST,
arXiv:2010.12279
Nelles, Seminar Oxford, 2021 (virtual) 22RNO-G Cosmic ray
The details and contributions tagging and high-
fidelity
reconstruction
Antennas
distributed for Combination of
neutrino vertex antennas for
reconstruction reconstruction of
full electric-field
RFover Fibre
strings, for high
signal quality and
Phased-array
signal
trigger for highest
reconstruction
effective volume
Nelles, Seminar Oxford, 2021 (virtual) 23arXiv:2010.12279
RNO-G
The science
• RNO-G ‘big’ enough to have a reasonable
chance to detect a continuation of the
diffuse IceCube neutrino flux
• Somewhat optimistic chance to detect
transient events, nice complimentary
Northern hemisphere sensitivity
re 13. Instantaneous sky coverage for different radio detector locations in declination and right
sion. The field of view is defined to cover the solid angle which contain 90% of triggering events
n isotropic flux. TheSeminar
Nelles, sky coverage
Oxford,was calculated
2021 (virtual) for a 60 m deep detector at the South Pole 24
n hash), for a 50 m deep detector at Greenland (orange solid), and for an ARIANNA stationRadio detection of neutrinos
Neutrino sensitivity
• RNO-G sensitive to all 3 neutrino flavors (NC and CC, > 10 PeV)
13
• 20% of all detections are
from interactions of secondary Garcia-Fernandez et al. (AN), Phys. Rev. D 102, 083011 (2020)
muons or taus
• Flavor-tagging relevant for
both particle physics and
astrophysics 3
n neutrinoNelles,
e↵ective
Seminar volumes for an
Oxford, 2021 (virtual) FIG. 13. Top panel: all-flavor neutrino e↵ective volumes for
25Radio detection of neutrinos
Reconstructing the energy
• Radio detection a mixture of “radio
interferometry” in a medium and particle physics
• Ingredients: vertex distance (scaling with
distance and attenuation), signal fluency (scales
quadratically with energy), neutrino inelasticity
PhD thesis, Christoph Welling, in progress
Nelles, Seminar Oxford, 2021 (virtual) 26Radio detection of neutrinos
Reconstructing the arrival direction
• A signal contains:
• Timing, i.e. signal arrival direction
• Frequency content, i.e. angle to Cherenkov
angle
• Polarization, i.e. radial angle on Cherenkov
cone
• All need to be combined for arrival direction
• Working towards multi-
messenger astronomy
with UHE neutrinos
PhD thesis, Ilse Plaisier, in progress
Nelles, Seminar Oxford, 2021 (virtual) 27Radio detection of neutrinos Where to after? IceCube-Gen2 Nelles, Seminar Oxford, 2021 (virtual) 28
IceCube-Gen2
Radio detection of neutrinos
• IceCube Collaboration has put forward a baseline design for IceCube-Gen2,
arXiv:2008.04323
• Main part is a much enlarged optical array with new DOMs, includes a large
radio array
• Together they will span the whole energy range from PeV to EeV
Diffuse (Fermi LAT) IceCube (ApJ 2015)
5
10 Cosmic rays (Auger) IceCube (tracks only, ApJ 2016)
Cosmic rays (TA) IceCube-Gen2 (10 years)
cm ]
2
6
10
1
sr
7
10
1
[GeV s
8
10
E ×
9
10
2
10
10
10-1 100 101 102 103 104 105 106 107 108 109 1010 1011 1012
Energy [GeV]
Nelles, Seminar Oxford, 2021 (virtual) 29IceCube-Gen2 — Phase 1, Phase 2, Phase 3
This is a big array!
A large project
• The IceCube Upgrade (similar to what
was previously known as PINGU) is the
first phase of IceCube-Gen2
Radio Array for Gen2 • Scheduled to start deployment next
200 stations. This is a big array! season, COVID-delays likely
Areal coverage: order 500 km^2
Autonomous power and communication
• Plans to deploy a fraction of the new
optical strings and the radio array
directly after the Upgrade as Gen2-
Phase2 (completion 2028)
• After the completion the full-design of
Gen2 will be built
Nelles, Seminar Oxford, 2021 (virtual) 30The radio array of Gen2
The design process
Radio
• AllArray for Gen2
previous radio experiments were small, we are going through multiple
200 stations. This is a big array!
iterations of internal reviewing
Areal coverage: order 500 km^2 now
Autonomous power and communication
• Full design and sensitivity in fall in 2021 (PDR)
Target sensitivity
Different variants of
Gen2 radio arrays
Nelles, Seminar Oxford, 2021 (virtual) 31Radio detection of neutrinos
IceCube-Gen2
“IceCube-Gen2 will play an essential role in shaping the new era of multi-messenger
astronomy, fundamentally advancing our knowledge of the high-energy universe.”
Diffuse (Fermi LAT) IceCube (ApJ 2015)
5
10 Cosmic rays (Auger) IceCube (tracks only, ApJ 2016)
Cosmic rays (TA) IceCube-Gen2 (10 years)
cm ]
2
6
10
1
sr
7
10
1
[GeV s
8
10
E ×
9
10
2
10
10
10-1 100 101 102 103 104 105 106 107 108 109 1010 1011 1012
Energy [GeV]
IceCube-Gen2: The Window to the Extreme Universe ,
https://arxiv.org/abs/2008.04323, Journal of Physics G, in press
Nelles, Seminar Oxford, 2021 (virtual) 32Conclusions
Radio detection: From ‘the odd’ technique to standard detection technique
• Air showers:
• Established working of the radio technique
• Showed high accuracy cosmic-ray measurement
• Ultra-high accuracy next step to come (SKA)
• Neutrinos:
Conclusion
• Radio detection seems the only cost-efficient way to built UHE detectors
(11.2") borehole will raise the high-pass freq. by ~30
• ~35Technology
MHz MHz has matured, RNO-G will be first large scale implementation
ntenna changes• low-pass
IceCube-Gen2
freq. but not high-pass,will feature a large radio array and discover UHE neutrinos
n mostly be mitigated via end-cap redesign.
~35 MHz change in high-pass big enough
to call for a VPol redesign?
~30 MHz
6
45 assembled VPol Antennas
Nelles, Seminar Oxford, 2021 (virtual) 33You can also read
