11th International Workshop on Acoustic and Radio EeV Neutrino Detection Activities

Jun 8, 2026, 1:00 PM → Jun 11, 2026, 5:00 PM Europe/Berlin

Schlosshotel Karlsruhe

Tim Huege (KIT)

The 11th installment of the workshop series on Acoustic and Radio EeV Neutrino Detection Activities, to be held in Karlsruhe, Germany, from June 8th to 11th 2026.

Mon, June 8

Other: Welcome

1 Welcome and Practicalities

Speaker: Tim Huege (KIT)

Overview

2 First data and performance of the Radio Detector of the Pierre Auger Observatory

The Radio Detector of the Pierre Auger Observatory measures radio emission from extensive air showers in the frequency range of 30–80 MHz. Covering an area of 3000 km², it constitutes the largest installation dedicated to the detection of cosmic particles, including charged cosmic rays, gamma rays, and neutrinos. Commissioning was completed at the end of 2024, and the radio antennas now operate in conjunction with the water-Cherenkov detectors of the Surface Detector array.
Over the coming decade, this hybrid detection approach is expected to deliver a unique dataset, providing clean and complementary information on both the electromagnetic and muonic components of extensive air showers. The primary scientific objective is to identify the sources of ultra-high-energy cosmic rays by determining the atomic mass and energy of the primary particles. These observables are combined to derive the particle rigidity, a key parameter for source identification.
In addition, the combined measurement of electromagnetic and muonic components will enable more stringent constraints on the flux of neutral particles at the highest energies.
First data will be presented, and the performance of the detector will be discussed.

Speaker: Jörg Hörandel (Radboud University Nijmegen)

3 Science Goals and Instrumentation of the Auger Radio Infill SKALA Extension (ARISE)

The Auger Radio Infill SKALA Extension (ARISE) at the Pierre Auger Observatory in Argentina measures cosmic-ray air showers in the energy region around 100 PeV. ARISE is comprised of 18 SKALA-2 antennas featuring two polarization channels each, deployed in 2025 within 100 m from a surface detector station in the enhancement area of the Pierre Auger Observatory. This area of the surface array features a denser spacing of 433 m between surface stations, each equipped with underground muon detectors. One of these surface detector stations provides a trigger for simultaneous readout of all ARISE antenna channels. The wide frequency range of ARISE, from 50-350 MHz, includes the subband of optimum signal-to-noise ratio for air-shower radio emission against Galactic radio background. In combination with the dense antenna spacing, this enables a relatively low detection threshold, and ARISE aims at demonstrating full detection efficiency for near-vertical air showers above 100 PeV. As an advantage over the current radio detectors at Auger, which are more efficient for inclined air showers, this would enable low systematic uncertainties for physics analysis combining ARISE radio measurements with coincident measurements of the underground muon detectors in the same area. In this presentation, we will provide an overview over the ARISE instrumentation operating at the Pierre Auger Observatory and will outline the science goals.

Speaker: Frank Schröder (University of Delaware and Karlsruhe Institute of Technology (KIT))

4 Radio self-triggering in GRANDProto300

GRANDProto300 (GP300) is the ongoing pathfinder array for the next-generation GRAND (Giant Radio Array for Neutrino Detection) ultra-high-energy astroparticle observatory. Since April of 2025, GP300 has operated as a 20 km² array of 65 detection units in northwest China. This location was strategically selected for its radio-quiet environment, which is essential for the array’s radio self-triggering capabilities and high-sensitivity detection of cosmic rays (and, eventually, neutrinos). Our current focus is optimizing the hardware and software of the data acquisition system. This is a critical step to ensure stable, continuous observation, as GP300 relies entirely on radio signals for self-triggering. In this talk, we will present the current status of GP300, including its ongoing expansion, and the latest implementation of the radio self-trigger system, including the detection of the first cosmic rays using this system.

Speaker: Pengxiong Ma (Purple mountain observatory,CAS)

5 Air-shower detection with the surface antennas at the IceCube Neutrino Observatory

IceTop is the surface air-shower array of the IceCube Neutrino Observatory measuring cosmic rays in the PeV – EeV energy range. Additional detectors of scintillators and antennas are to be deployed in the IceTop footprint as part of the Surface Array Enhancement. The scintillators aim to reduce the energy threshold to the TeV regime and the antennas provide information on mass-sensitive observables such as $X_{max}$. Since early 2025, three stations, each comprising 3 antennas and 8 scintillators with an independent data acquisition system, are running in tandem with the ice-Cherenkov tanks of IceTop. First air-shower measurements measured with all 9 antennas are presented. Additionally, with the goal of calibrating the antennas with the galactic noise, the sidereal modulation of background radio data is also evaluated.

Speaker: Megha Venugopal (Karlsruhe Institute of Technology)

6 Detection of Scintillator-Triggered Cosmic Rays with the BEACON Prototype

The Beamforming Elevated Array for COsmic Neutrinos (BEACON) is an ultrahigh energy neutrino detector concept consisting of hundreds of phased radio arrays placed on mountaintops, searching for the geomagnetic emission of up-going extensive air showers created by Earth-skimming tau neutrinos. A prototype of the BEACON concept, consisting of a single phased radio array, operated in the White Mountains of California from 2018 to 2025. In 2023, an array of four scintillators was deployed, co-located with the radio array, to validate the detection of down-going extensive air showers initiated by cosmic rays. In this talk, we detail a cosmic ray search performed using scintillator-triggered radio data. Overall, we identify 20 cosmic ray candidates on a background of 0.1 events. In the future, we plan to use this analysis to improve the radio-only beamforming trigger and to validate our predicted neutrino sensitivity.

Speaker: Andrew Zeolla (Institut d'Astrophysique de Paris)

7 The Payload for Ultrahigh Energy Observations Design and Science Reach

The Payload for Ultrahigh Energy Observations (PUEO) is a NASA Long Duration Balloon-borne mission that flew over Antarctica for 23 days starting in December 2025. PUEO is sensitive to neutrinos interactions in the Antarctic ice that result in Askaryan emission and geomagnetic emission from cosmic rays and tau neutrinos. These neutrinos may arise from cosmogenic neutrinos produced during the propagation of the highest energy cosmic rays or from astrophysical neutrinos at the sources. The main instrument consists of 96 dual-polarized quad-ridged horns operating in the 300-1200 MHz range, while the low frequency instrument includes 8 dual-polarized sinuous antennas sensitive to the 50-500 MHz range. Signals from multiple antennas in the main instrument form beams at the trigger level that enhance the instrumental sensitivity. In this talk, we will present the design and science capabilities of the experiment and include discussion of the planned diffuse and source searches.

Speaker: Stephanie Wissel (Penn State)

3:10 PM Coffee Break

Overview

Convener: Tim Huege (KIT)

8 The Radio Neutrino Observatory in Greenland (RNO-G): Status Update and Recent Results

The Radio Neutrino Observatory in Greenland (RNO-G) is a next-generation radio detector designed to observe ultra-high-energy (UHE) neutrinos above 10^16 eV via the Askaryan effect. RNO-G currently consists of eight autonomous stations, with a total of 35 stations planned for construction over the next few years. Each RNO-G station includes a set of deep antennas deployed on strings up to a depth of 100 m and a set of shallow antennas that both act as a veto for surface backgrounds and contribute to the neutrino effective volume. The deep antennas are equipped with a phased array trigger that is the primary mechanism for detecting neutrino events.

In this contribution, I will discuss the current status of RNO-G, including advancements in hardware development, calibration strategies, and simulation progress. I will also highlight some recent results from RNO-G, including our searches for cosmic ray signals, our identification of various backgrounds including solar flares and airplanes, and our progress towards an array-wide neutrino search.

Speaker: Kaeli Hughes (The Ohio State University)

9 The First Array-Wide Diffuse Flux Search for UHE Neutrinos with ARA

The Askaryan Radio Array (ARA) is an ultra-high energy (UHE) neutrino detector at the South Pole that searches for impulsive broadband radio signals from neutrino-induced particle showers in glacial ice. ARA comprises five autonomous stations deployed at the South Pole, each instrumented with antennas deployed up to 200 meters below the ice surface and sensitive to both vertically and horizontally polarized signals. With over a decade of accumulated livetime, ARA provides the largest exposure yet achieved by any in-ice radio array.

We present the first array-wide diffuse UHE neutrino search using the ARA dataset taken from 2013 to 2023. Building on previous ARA analyses, this search benefits from substantial improvements in detector characterization and simulation, including data-driven models of noise and electronics, revised antenna responses, and upgraded neutrino interaction and lepton propagation modeling. Additionally, this search brings together the array-wide dataset within a unified analysis framework for waveform processing, background modeling, background rejection, and array-wide cut optimizations.

This search is expected either to identify the first UHE neutrino candidates observed by any in-ice radio neutrino detector, or to set the most stringent limits to date on the diffuse UHE neutrino flux above a few EeV. More broadly, this search informs the analysis and simulation strategies required for next-generation large-scale radio arrays such as RNO-G and IceCube-Gen2 Radio.

Speaker: Marco Muzio

10 The Radar Echo Telescope

The Radar Echo Telescope (RET) experiment aims to probe the cosmic neutrino flux at >PeV energies using radar. We present our latest results, discussing the RET-CR pathfinder experiment deployed at Summit Camp, Greenland. The RET-CR experiment aims to detect the in-ice continuation of high-energy cosmic-ray-induced particle cascades hitting the ~3km altitude Greenlandic ice sheet. The in-air cascade is tagged through the RET-CR surface scintillator component that also aids in the event reconstruction. Once detected, a trigger is sent to the in-ice radar system and its data is read out to search for the radar echo from the particle cascade in-ice continuation. We show first results of our ongoing data analysis and present our simulation framework.

Speaker: Krijn de Vries (Vrije Universiteit Brussel - IIHE)

Acoustics

Convener: Robert Lahmann (University Erlangen-Nuremberg/ECAP)

11 Tracking of acoustic sources using KM3NeT/ARCA acoustic positioning system elements

The KM3NeT/ARCA (KM3 Neutrino Telescope / Astroparticle Research with Cosmics in the Abyss) detector, currently under construction in the Mediterranean Sea, employs a large-scale Acoustic Positioning System (APS) to continuously monitor the positions of the detection elements with high accuracy. The APS is a distributed phased-array system composed of a large number of digital acoustic sensors integrated into the Digital Optical Modules (DOMs) and into the seafloor anchors (bases) of the Detection Units (DUs), together with a long-baseline network of acoustic emitters on the seabed. Continuous sampling at 195.3 kHz and real-time data streaming to shore enable precise monitoring of the detector geometry, which is essential for the reconstruction of neutrino directions using optical Cherenkov radiation. The system forms a densely instrumented acoustic network, with sensor positions reconstructed with an accuracy of the order of tens of centimeters. In this work, we evaluate the accuracy of the system in reconstructing the location of high-frequency acoustic sources through multi-lateration and advanced time-of-arrival techniques. These techniques are currently being investigated for their potential applicability to acoustic neutrino detection.

Speaker: Salvatore Viola (Istituto Nazionale di Fisica Nucleare - Laboratori Nazionali del Sud)

12 Acoustic Characterization of the KM3NeT/ARCA Site for Ultra-High-Energy Neutrino Detection

The acoustic detection of Ultra-High-Energy (UHE) neutrinos has emerged as a promising technique for probing the highest-energy regime of neutrino astrophysics. The recent observation of a UHE event by the KM3NeT detector has further strengthened interest in complementary detection methods beyond the standard Cherenkov approach. At the KM3NeT/ARCA site, deployed at a depth of 3500 m and located 100 km offshore Capo Passero (Sicily), INFN-LNS operates a long-baseline array of three hydrophones continuously recording acoustic data since 2024 with a sampling rate of about 195 kHz and calibrated from few Hz up to 90 kHz. These hydrophones offer the opportunity to perform a long-term monitoring of the acoustic soundscape and evaluate expected signal to noise ratio in the frequency range relevant for neutrino-induced signals. This paves the way to explore the feasibility of acoustic neutrino detection at the Capo Passero Site.A statistical analysis of the ambient noise at the KM3NeT/ARCA site using more than 2 years of continuous data taking. In addition, preliminary studies on signal identification techniques are reported, aimed at identifying neutrino-like induced acoustic signatures from the measured background.

Speaker: Abdelghani Idrissi (INFN - LNS, Unict-DFA)

13 The INFN-LNS subsea cabled infrastructure: a unique testbed for R&D on UHE neutrino acoustic detection

The subsea cabled infrastructure of LNS-INFN continuously expands both in number of observing systems, and in capacity to host new assets.
Since 2024, the historical Test Site offshore the port of Catania, at 2100 m water depth, has been upgraded with the installation of a short-baseline, large bandwidth tetrahedral antenna, deployed in the framework of the IPANEMA project.
In 2025, a Distributed Acoustic Sensing (DAS) system acquired by CSFNSM under the VONGOLA project was permanently connected to the underwater cable, enabling joint testing of complementary techniques for acoustic soundscape monitoring and studies,.
Meanwhile, at the Capo Passero Site—primarily dedicated to the KM3NeT ARCA detector—another DAS unit was connected to the main electro-optical cable under the EU LowNoiser project.
In addition, a set of three seafloor hydrophones, deployed at relative distances of about 100 m, continuously streams data allowing long term study of noise in the band between few tens Hz and 70 kHz.
Finally, a new subsea data and power hub for multidisciplinary science, funded under the ITINIERIS project, has been built and it will be deployed soon.
Alongside this extensive hardware upgrade, several software tools for soundscape analysis and sound cataloguing have been developed, relying both on standard DSP methods and on new AI techniques.
A FAIR-oriented approach for data preservation has also been implemented and shared with project stakeholders.
This combination of Several acoustic sensors, multiple connection ports, and advanced software tools provides unprecedented opportunities to study the acoustic detection of ultra high energy (UHE) particles in the deep sea.

Speaker: Giorgio Riccobene (INFN LNS)

14 Distributed Fiber Optic Sensing as a Next‑Generation Platform for Acoustic UHE Neutrino Detection?

Emerging optoacoustic sensing technologies offer a promising pathway for advancing the acoustic detection of ultra–high energy (UHE) neutrinos in the deep sea. Distributed Fiber Optic Sensing (DFOS), and in particular Distributed Acoustic Sensing (DAS), enables the transformation of standard submarine telecommunication fibers into dense arrays of virtual hydrophones, with measurement points spaced at the meter scale along tens of kilometres. Recent developments in DFOS on subsea telecom cables have demonstrated the capability to monitor acoustic fields over basin scale distances, providing continuous, wide aperture coverage well suited for detecting impulsive pressure waves expected from neutrino induced thermoacoustic cascades. Within this context, the INFN cabled seabed network installed offshore Capo Passero (South-East Sicily) serving the KM3NeT neutrino telescope may represent an ideal testbed for next generation neutrino acoustic detection. A DAS system is already operating using the 100km long main electro optical cable to monitoring underwater soundscape up to 500 Hz. Novel DFOS based devices connected to short cable trunks could provide a wide area, continuously operating, and scalable acoustic observatory for the exploration of the highest energy neutrinos. Leveraging the unique features of the INFN seafloor network, we discuss the scientific potential and technical prospects of applying advanced optoacoustic sensing to neutrino astrophysics in the Mediterranean Sea.

Speakers: Abdelghani Idrissi (INFN - LNS, Unict-DFA), Giorgio Riccobene (INFN LNS), Salvatore Viola (Istituto Nazionale di Fisica Nucleare - Laboratori Nazionali del Sud)

Other: Welcome Reception

Tue, June 9

Analyses/Results

15 Radio measurements of air showers with the IceCube-Gen2 surface prototype station at the Pierre Auger Observatory

The design of the IceCube-Gen2 observatory, proposed as a next-generation extension of IceCube, includes a surface array consisting of scintillators and radio antennas. In addition to several such detectors already deployed at IceCube’s surface array at the South Pole, a prototype station including 3 SKALA antennas has been operating at the Pierre Auger Observatory for several years. This setup has been used to successfully observe radio signals from air showers, demonstrated through coincident observations with the Auger Surface Detector. In this contribution, we present an updated analysis of these radio signals, and compare them to CoREAS simulations using the reconstruction from the Auger Surface Detector as input.

Speaker: Stef Verpoest (University of Delaware)

16 First Air-Shower Measurements with the Auger Radio Infill SKALA Extension (ARISE)

The Auger Radio Infill SKALA Extension (ARISE) was installed in 2025 at the Pierre Auger Observatory to detect the radio emission in the band of 50-350 MHz of near-vertical cosmic-ray air showers at energies of 10s to 100s PeV. The array comprises 18 SKALA-2 antennas deployed around one of the surface-detector stations of the 433m infill array (SD-433), which provides the trigger for ARISE. We present first measurements with ARISE and show the detection of radio pulses associated with extensive air showers. Radio signals are found in coincidence with SD-433 events, and a comparison of the arrival directions reconstructed from the radio and surface detector signals confirms the measurement of air showers with ARISE. These observations provide a first assessment of the detector setup and demonstrate the potential of ARISE for radio detection of near-vertical air showers.

Speaker: Carmen Merx (KIT/IAP)

17 Determining the absolute energy scale of cosmic-ray measurements with AERA

Determining the absolute energy scale in cosmic-ray observations is both challenging and of fundamental importance. We show that radio measurements of extensive air showers with the Auger Engineering Radio Array, combined with per-event CoREAS simulations, enable an accurate calibration of the cosmic-ray energy scale between 3 x $10^{17}$ eV and several $10^{18}$ eV. To ensure an accurate result, we control individual systematic uncertainties at the 5% level or better. The absolute calibration of the antenna gain and the analog signal chain is performed using the Galactic background emission and detailed antenna gain modeling, cross-checked with laboratory measurements. Further key elements include temperature-dependent amplification corrections, continuous detector monitoring, thunderstorm vetoing, unbiased event reconstruction, and per-event atmospheric modeling. The resulting AERA energy scale is 12% higher than the one established with the Auger Fluorescence Detector, consistent within uncertainties and providing an independent confirmation of the absolute energy scale of the Pierre Auger Observatory.

Speaker: Tim Huege (KIT)

18 Searching for Cosmic Rays in the Deep Antennas of RNO-G

The Radio Neutrino Observatory in Greenland (RNO-G) is designed to detect neutrinos at ultra-high energies, exploiting Askaryan emission in ice. However, this emission is not exclusive to neutrinos. Cosmic ray air shower cores can continue cascading in the ice, producing Askaryan emission that in limited cases cannot be rejected by simple vetoes. Rather than being purely a background concern, these neutrino-like cosmic ray signals also provide validation of the detection pipeline using real impulsive events, complementing simulation-based approaches. The significantly higher cosmic ray flux in the relevant energy range also makes this a practical calibration source. This work presents progress on RNO-G's cosmic ray search in its deep antennas, where the neutrino sensitivity is highest and cosmic ray identification is critical.

Speaker: Bryan Hendricks

19 Observation of In-ice Askaryan Radiation from High-Energy Cosmic Rays

The Askaryan Radio Array (ARA) is a neutrino detector located at the South Pole that searches for radio emission from ultra high energy neutrino interactions within Antarctic ice. While ARA is primarily a neutrino detector, it is also sensitive to Askaryan emission from cosmic ray air showers that develop at the surface of the ice. ARA consists of five autonomous stations, each with vertical and horizontal antennas deployed up to 200 m in the ice.
Here, we present the first experimental evidence of Askaryan emission detected in naturally-occurring ice from cosmic ray events, after a re-analysis of data taken with the fifth ARA station during the 2019 season. The signal shape, arrival direction, electric field polarization, and event rate are consistent with what we would expect from theoretical predictions and inconsistent with the combined background estimate at a level of 5.1 sigma. The brightest events are additionally consistent with an extended cascade-like emission pattern.

Speaker: Kaeli Hughes (The Ohio State University)

20 Evidences for Combined Geomagnetic and Askaryan Emission in a CR Candidate Event

The Askaryan Radio Array (ARA) is a radio neutrino detector designed primarily to detect neutrinos with energies above 10 PeV. In addition to neutrinos, ARA is also sensitive to radio emission from cosmic-ray(CR)–induced air showers. Detection of these emissions can support detector calibration, improve the detection capabilities of the detector, and help model CRs as a background for neutrino searches. The detector currently consists of five autonomous stations, including one phased-array station. Each station contains 16 radio antennas deployed at depths of up to 200 m in the Antarctic ice.

ARA Station 2 (A2) recorded a double-pulse event that passed all background-rejection criteria used in a neutrino search analysis. This event is hypothesized to originate from a CR-induced air shower, where the first pulse is produced by in-air geomagnetic emission and the second pulse arises from in-ice Askaryan emission generated by a downward-propagating CR-induced air shower.

We present a Monte Carlo simulation study of the expected CR event topology based on a fitted model. The results show close agreement between simulations and data in terms of the time delay between the two pulses, the reconstructed arrival directions of the signals, and their polarization characteristics. These results support the CR interpretation of the event and demonstrate the capability of ARA to detect such rare signatures.

Speaker: Kenneth Couberly (University of Kansas)

10:30 AM Coffee

Analyses/Results

21 The Low-Frequency Instrument for the Payload for Ultrahigh Energy Observations (PUEO)

The Payload for Ultrahigh Energy Observations (PUEO) is a long-duration balloon experiment designed to detect ultra-high-energy (UHE) neutrinos with energies above 1 EeV. The instrument consists of a Main Instrument (MI) mounted on the payload and a Low-Frequency (LF) instrument deployed beneath the payload. The LF instrument comprises eight sinuous antennas operating in the 50–500 MHz band, complementing the 96 dual-polarized horn antennas of the MI, which covers the 300–1200 MHz range. The LF system is optimized to detect radio emissions from air showers induced by cosmic rays and Earth-skimming tau neutrinos. By extending sensitivity to lower frequencies, the LF instrument enhances PUEO’s capability to characterize signals and improve event reconstruction. In this talk I will review PUEO’s science goals and instrument performance during its successful flight from December 19, 2025 to January 11, 2026, with particular emphasis on the design, implementation, and performance of the LF system.

Speaker: Yuchieh Ku (Pennsylvania State University)

22 The Flight of the PUEO

The Payload for Ultrahigh Energy Observations (PUEO), a NASA long duration balloon payload seeking to detect ultrahigh energy particles using the radio technique, flew over Antarctica for 23 days this Austral summer. This talk will discuss the performance of PUEO during the flight, covering the trigger, attitude systems, background and telemetry systems. I will also present the latest progress on calibration and discuss progress on analyzing the dataset.

Speaker: Cosmin Deaconu (University of Chicago)

Calibration/Backgrounds

23 Wind Related Background Radio Pulses at the Radio Neutrino Observatory in Greenland

During periods with high wind speeds (> 8 − 10 m/s) an overwhelming number of radio pulses are detected with RNO-G. This effect has also been reported by other polar radio experiments, and, more recently, also by experiments in sandy environments. This poses a significant challenge for the identification of cosmic particles during those times. Periods with strong winds are not only very common in Greenland, but, during the polar winter, wind is the only renewable energy source available to keep the autonomus stations operational. In this contribution, the current state of knowledge about wind-related backgrounds is discussed, as well as plans of how to further investigate them within RNO-G and with dedicated set-ups.

Speaker: Pascal Schriefer (ECAP / Friedrich-Alexander-Universität Erlangen-Nürnberg)

24 The Triboelectric Effect at the Pierre Auger Observatory

With the AugerPrime extension of the Pierre Auger Observatory all surface detector stations have been equipped with radio antennas to measure extensive air showers in the 30-80 MHz band.
For the data acquisition using a trigger based on radio pulses, the triboelectric effect has been reported to be responsible for an increased background rate at high wind speeds for ice-based radio experiments. With the self-triggered data of the Auger Engineering Radio Array (AERA) we estimate the correlation between trigger rate and wind speed.

Speaker: Julian Rautenberg (Bergiscche Universität Wuppertal)

25 Near-horizon transient backgrounds for radio experiments

Radio telescopes that aim to find astroparticles rely on the detection of impulsive, short-lived and transient radio signals produced primarily via the geomagnetic emission effect. One of the main challenges of this detection method is the presence of abundant radio backgrounds produced by human activity, both continuous (as in intentional emission for telecommunications) and impulsive (for example, unintentional emission associated with the use of large electrical currents and voltages). It is impossible to separate the origin of impulsive signals (astrophysical or anthropogenic) if they have very similar shapes.
Therefore, radio telescopes are usually placed in remote and geographically advantageous regions where the radio background is the lowest, and they carefully characterize their continuous radio backgrounds near the horizon in order to perform their research. Transient radio telescopes have also focused on near-vertical radio emission, which allows for a closer match to our models of geomagnetic emission.
However, next-generation radio detectors aim to also detect radio signals from near-horizontal sources, in particular the interactions of Earth-skimming neutrinos. Modelling of radio propagation near the surface of Earth needs to include complex geometrical effects and include possible interactions with the non-smooth lower layers of the atmosphere. This need is further evidenced by reports from multiple radio observatories of an excess of near-horizon impulsive signals that could not be reconciled with sources at the horizon so-far.
In this work, we consider the possibility of secondary radio reflections of originally terrestrial sources as the cause of the near-the horizon excess transient events.
A simple model of low-altitude clouds shows that they cannot be ruled out as the source of sporadic radio reflections.

Speaker: Anna Nelles

26 Investigating Radio Frequency Interference from Satellite Constellations at the Radio Neutrino Observatory in Greenland.

The proliferation of low-earth-orbit satellites over the last decade has significantly increased the risk of radio frequency interference with ground-based radio astronomy experiments. Unintentional, narrow-band emission at protected frequency bands, as well as broadband emission from such satellites have been conclusively detected by radio experiments like LOFAR, NenuFAR and SKA.

Experiments targeting the radio detection of neutrinos — such as RNO-G and IceCube-Gen2 — may be similarly affected with different consequences. Unintentional radio signals, both narrowband or broadband, may cause false-positive triggers, which reduces the trigger efficiency to real particle-based signals. In the worst case, this would lead to a reduced neutrino-search sensitivity.

Thus far, no systematic study has addressed this risk in the context of radio-neutrino detection. In this contribution we present an analysis of two years of RNO-G data, characterising radio frequency interference from large satellite constellations including Starlink and OneWeb, and estimate their impact on experiment live-time and false-trigger rate.

Speaker: Annanay Jaitly (DESY Zeuthen | RNO-G)

12:30 PM Lunch

Calibration/Backgrounds

27 Relative Calibration of the AugerPrime Radio Detector at the Pierre Auger Observatory

Radio emissions of extensive air showers can be observed with the AugerPrime radio detector (RD) at the Pierre Auger Observatory. As part of the AugerPrime upgrade, RD has been installed on $1660$ water-Cherenkov detectors on an area of roughly $3000 \text{ km}^2$ and consists of dual-polarized Short Aperiodic Loaded Loop Antennas (SALLA). To achieve high measurement precision, the SALLA must be well calibrated, which requires the antenna response pattern to be well known. Here, we introduce a direction-dependent relative calibration using a well-defined biconical antenna mounted to a drone. The drone-based setup possesses active stabilization and precise aiming with the use of a gimbal. Additionally, the position of the drone is tracked using differential GPS with a precision of up to $1$ cm. This setup allows us to precisely extract the antenna response pattern from any arrival direction. In an in-situ campaign in November 2023, calibration measurements of the RD were performed. Building on that experience, a second calibration campaign was carried out in March 2026 with an improved setup and procedure. A novel approach based on Information Field Theory is implemented to reconstruct the full antenna response pattern across all arrival directions and frequencies from a set of sparse measurements. First results of the full antenna response pattern are presented.

Speaker: Alex Reuzki (RWTH Aachen University)

28 A in-situe absolute gain calibration for the in-ice radio neutrino detector RNO-G

The Radio Neutrino Observatory Greenland (RNO-G) utilizes a network of in-ice radio antennas to detect the radio emission from ultra-high-energy neutrinos interacting with the ice. To reconstruct neutrino properties, such as energy and direction, an accurate calibration of the detector response is indispensable. In RNO-G, the complex interplay between electrical and optical components make a pre-deployment laboratory calibration insufficient, necessitating an in-situ calibration approach. In analogy to the well-established galactic calibration in air-shower radio detectors, we have developed a novel method which uses, in addition to a sub-dominant galactic component and system noise, the thermal radiation from the surrounding ice as a ``standard candle'' for an absolute gain calibration.
In this contribution, we introduce the novel concept of the in-situ absolute gain calibration for RNO-G, present preliminary results from the first calibration campaign, and discuss the implications for neutrino detection and future improvements.

Speaker: Felix Schlüter (Free University Brussels (ULB))

29 HiCal3: Calibration of PUEO

The Payload for Ultrahigh Energy Observations (PUEO) is a long duration balloon
experiment that flew over Antarctica for 23 days from December 2025 to January
2026. Approximately 24 hours after the launch of the PUEO, two high altitude
calibration balloon payloads (HiCal3a and HiCal 3b) were launched and followed
the PUEO. The HiCal payloads contained high voltage pulse generators that
transmitted signals in both vertical and horizontal polarizations. These signals
were captured by the PUEO during flight and are being used to calibrate the
instrument. This talk will present the design and flight of the HiCal payloads
as well as ongoing analysis of HiCal calibration signals.

Speaker: Kenny Couberly

30 Precision Measurements of the Firn Refractive Index for RNO-G

We present a measurement of the refractive index of firn ice at Summit Station, the site of the Radio Neutrino Observatory in Greenland (RNO-G). The refractive index profile was determined, without relying on density data, by using absolute time-of-flight measurements with sub-nanosecond precision. We establish the consistency of these findings across several locations near Summit Station and both pulse polarizations. From these findings, we derive multiple parametrized models of the firn ice and their respective uncertainties. Furthermore, we test the consistency of the derived models with additional pulser measurements and compare the results to independent measurements of the density.

Speaker: Nils Heyer (Uppsala University)

31 Seasonal ice evolution: implications for UHEN detection and reconstruction

The upper 100 - 200 m of the polar ice sheet, known as the firn layer, undergoes seasonal variations in density and temperature that modify its refractive index profile. These changes lead to variations in received signal power and arrival time for radio signals propagating through near-surface regions of the firn. In the absence of time-dependent ice models, this introduces an irreducible background uncertainty in the reconstructed energy and arrival direction of neutrinos and cosmic rays for a range of source positions relative to the detector, with variations of $\mathcal{O}(10 \%)$ in signal power and reconstructed energy, and $\mathcal{O}(0.1^{\circ}–1^{\circ})$ in arrival direction. We present a simulation study quantifying the impact of seasonal firn variability on reconstruction performance for both shallow and deep radio neutrino detectors. In addition, we report measurements of ice properties at the Radar Echo Telescope for Cosmic Rays (RET-CR) site in Greenland, combining in-situ density measurements with radar-based reconstructions, and demonstrate how these measurements can be used to constrain ice models for event reconstruction.

Speaker: Dr Alexander Kyriacou (Université libre de Bruxelles)

New Projects/Concepts

32 POEMMA Balloon with Radio: a POEMMA pathfinder mission and unique opportunity to study High-Altitude Horizontal Air Showers

The Probe Of Extreme Multi-Messenger Astrophysics (POEMMA) is a proposed mission designed to observe ultra-high-energy cosmic rays and cosmic neutrinos using space-based measurements of extensive air showers. A precursor to this mission is POEMMA Balloon with Radio (PBR). Scheduled for launch in 2028 from Wanaka, New Zealand, PBR will operate at a suborbital altitude of approximately 33 km. Through the combined use of multiple instruments, PBR will enable a multi-wavelength study of air showers. Its payload features a fluorescence camera, an air-Cherenkov camera and a radio instrument triggered by the latter. The radio instrument consists of two dual-polarized receiver channels equipped with broadband sinuous antennas sensitive in the 60–500 MHz band. This radio instrument is essential to achieving one of PBR’s science goals: the detection and characterization of the radio emission of High-Altitude Horizontal Air Showers (HAHAs) which are inaccessible to traditional ground-based detectors. The simulation of radio emission from HAHAs is performed using two independent software packages, CoREAS and ZHAireS-RASPASS. This contribution presents an overview of the PBR mission and its radio instrument, and details the ongoing preparatory analysis focused on characterizing the expected radio signals from the HAHAs that PBR aims to detect.

Speaker: Paula Gálvez Molina (University of Delaware)

33 An Overview of HERON: the Hybrid Elevated Radio Observatory for Neutrinos

The Hybrid Elevated Radio Observatory for Neutrinos, or HERON, is a new detector concept for ultrahigh energy (E > 100 PeV) neutrinos. HERON consists of 24 compact phased radio arrays embedded within a larger sparse array of 360 standalone antennas, deployed along the side of a ~100 km mountain range in Argentina. The phased arrays provide high sensitivity to the geomagnetic emission of up-going extensive air showers initiated by Earth-skimming tau neutrinos, while the sparse array provides an excellent pointing resolution and offline event reconstruction capabilities. The long in-air propagation length of radio combined with the huge area in-view from each high-altitude site gives HERON a very large instantaneous effective area. HERON will thus have the highest sensitivity to UHE neutrino fluences from short-duration astrophysical transients at the time of its completion. In this talk, we detail the HERON concept, future prototyping and deployment efforts, and the science that will be conducted over the next several years.

Speaker: Andrew Zeolla (Institut d'Astrophysique de Paris)

3:15 PM Coffee

New Projects/Concepts

34 Status of SWGO-TURBO: interferometric radio detection of air showers at the Southern Wide-field Gamma-ray Observatory

The Utility for Radio Beam-formed Observations (TURBO) will be a $1$ km$^2$ radio array of about $800$ radio antennas planned as part of the Southern Wide-field Gamma-ray Observatory (SWGO). The array will detect pulsed radio emission from extensive air showers in the 50–200 MHz frequency band and be triggered by Water-Cherenkov Detectors. It aims to enhance SWGO’s sensitivity and effective aperture for photons above PeV energies and to allow more detailed and hybrid observations of charged cosmic-ray air showers. We will discuss the science case of SWGO, demonstrate the interferometric reconstruction technique, and present the current plans and status of the TURBO antenna design and array layout.

Speaker: Bjarni Pont (Radboud University)

35 Towards air shower observations with SKA-Low

Construction of SKA-Low is well underway in Australia. This telescope has a dense core of almost 60,000 antennas within a single square kilometer, and will offer a unique opportunity to measure air showers between the knee and the ankle regions in unprecedented detail. This is a critical energy range for probing the most powerful Galactic accelerators and the onset of the extragalactic component. The wide measurement bandwidth (50 - 350 MHz), sheer number of antennas that will observe air shower signals, and relatively uniform coverage of the radio footprint will allow for the most precise air shower measurements ever made. Using standard methods, we have demonstrated that with the SKA-Low we can achieve an Xmax precision of better than 8 g/cm$^2$ between $10^{16.6}$ eV and $10^{18}$ eV. Using new reconstruction methods, we expect to be able to reconstruct the full air shower development over a wide energy range, potentially down to PeV levels. At these energies, efficient photon/hadron separation could provide an opportunity to measure PeV gamma-ray air showers. Additionally, SKA-Low opens up a window to study high-energy hadronic interactions using anomalous air showers.

To facilitate air shower measurements at SKA-Low, we are building a radio-quiet particle detector array that will be installed at the SKA-Low core. This array will be used for triggering radio readout, as well as complementing radio measurements with information about the muonic air shower content. This will provide additional mass-sensitive information, and a way to study hadronic interactions. In this contribution, we give an overview of the cosmic-ray detection program, prospective analyses, and status of the particle detector array.

Speaker: Katie Mulrey (Radboud)

36 Prospects of detecting PeV gamma rays with SKA-Low

The detection of astrophysical photons of the highest energies is an important goal of modern gamma-ray astronomy and will improve our understanding of sources of cosmic ray acceleration in our Galaxy. While current generation gamma-ray observatories have barely reached the PeV energy range, higher energies still remain elusive, as they require large areas and efficient gamma-hadron separation. Furthermore, ultra-high energy (UHE) gamma rays were so far only detected using optical or particle detectors while radio detection of UHE photons is still missing. This might change with the SKA-Low observatory which is currently under construction.
The SKA-Low detector will be the most dense radio antenna array in the world, encompassing approximately 60000 broadband antennas (50 – 350 MHz) in its dense core. Currently, the energy threshold for radio detection of extensive air showers lies in the tens of PeV range for the signal to be visible in single antennas. However, this threshold can be lowered to a few PeV by exploiting SKA-Low's unprecedented antenna density using near-field beamforming. This contribution presents results that point to the possibility of a first detection of UHE gamma rays with radio and discusses the associated challenges.

Speaker: Philipp Laub (Erlangen Center for Astroparticle Physics - FAU Erlangen-Nürnberg)

37 Detection of cosmic-rays at over 100 MHz and multi-GHz frequencies with radio telescopes

In the past two decades, the radio detection of cosmic-ray extensive air showers (EAS) has developed into a technique with a resolution on cosmic-ray properties that is competitive with other observation techniques, at relatively low cost and high uptime. The results of existing radio cosmic-ray experiments have shown good agreement with other measurements as well as predictions from particle-level Monte-Carlo simulations. However, to date, almost all radio measurements have focussed on the frequency range below 100 MHz. While the emission generally is expected to be weaker at higher frequencies, both analytic coherence considerations and detailed simulations also predict the presence of a new polarization pattern due to synchrotron radiation. This contribution will present some preliminary studies into the detection of this feature in the several-100 MHz frequency range using detectors such as LOFAR 2.0 or SKA-Low, as well as the feasibility of detecting cosmic-ray radio emission at several-GHz frequencies using SKA-Mid.

Speaker: Sjoerd Bouma (ECAP)

38 Imaging Atmospheric Radio Telescopes: a new look into the radio emission from extensive air showers

A new way of imaging an extensive air shower through its radio emission will be presented. A modification to ZHAireS has been made to simulate an ideal radio telescope and demonstrate its capabilities. With it, the essential properties of imaging the radio emission from air showers and similarities to imaging atmospheric Cherenkov telescopes will be discussed. Lastly, a new form of radio emission arising from the angular discretization of the observer’s field of view will be presented.

Speaker: Juan Ammerman-Yebra (Radboud University)

39 Hybrid radio and particle detection of air showers: potential for ultra-high-energy gamma-ray identification

The autonomous radio-detection of extensive air showers initiated by ultra-high-energy (UHE) particles arriving with very inclined zenith angles has seen significant advancements in recent years, with several large-scale surface arrays planned and prototypes already in operation. Hybrid arrays combining radio antennas and scintillators, could serve as competitive UHE photon detectors. Indeed, for inclined showers, radio emissions can be detected by antennas for both cosmic-ray and photon primaries, while the muon-rich signatures of the former would typically trigger the scintillators. In this talk, I will show that effective separation between the two types of showers could be achieved in a hybrid radio antenna and scintillator setup, using two key observables—the total root mean square of the radio signal and the total energy deposit recorded in the scintillators. As a case study, I will apply this method to the layout of the prototype of the Giant Radio Array for Neutrino Detection (GRAND), GRANDProto300, complemented by Telescope Array-type scintillators. Such a hybrid array could set competitive upper limits on the integral photon flux in the energy range of 0.1 to 3 EeV, opening a yet uncharted territory for photon searches at UHE, by targeting very inclined air showers.

Speaker: Paul Minodier (Institut d'Astrophysique de Paris)

40 Detecting inclined air showers with small-scale radio antenna arrays

Large-area detector arrays such as the Pierre Auger Observatory and the Telescope Array (TA) have made significant progress in detecting inclined cosmic-ray air showers (with zenith angles > 60°), which provide a powerful tool for studying ultra-high-energy particles. Combining a sparse antenna array with surface detectors, the Auger Engineering Radio Array (AERA) has already detected inclined air showers with an angular resolution of 1.4°. It has therefore been commonly assumed that detecting such showers with higher reconstruction precision requires a very large-scale detector array, whereas most existing radio detection arrays cover only relatively small areas.
Recently, progress has been made in the radio-signal modeling of inclined air showers, and the associated reconstruction techniques are being optimized. Moreover, the unprecedented antenna density of the Square Kilometre Array (SKA) enables ultra-high-precision measurements within a small footprint. This opens up the possibility of precisely reconstructing large-zenith-angle air showers by fitting data from small-scale arrays—even when the shower cores lie outside the antenna array.
In this work, we use simulated data to investigate the feasibility of detecting large-zenith-angle air showers with SKA-Low. The ability to detect large-zenith-angle air showers using small-area arrays would greatly enhance the performance of relevant experiments.

Speaker: Chao Zhang (Nanjing University)

Wed, June 10

Simulations/Simulation Studies

41 Simulating an Imaging Atmospheric Radio Telescope

Currently imaging atmospheric Cherenkov telescopes provide the most precise TeV gamma-ray measurements, but are limited to a duty cycle of about 15% due to their reliance on clear, moonless nights. Building on this idea, a novel imaging atmospheric radio telescope could combine radio detection with powerful imaging-based reconstruction while enabling observations with a duty cycle close to 100%.

We present a simulation based on the Huygens–Fresnel principle, which models radio-wave propagation beyond the far-field approximation while reproducing aberrations predicted by geometric optics.

Our simulation enables the formation of radio images from arbitrary electric field inputs. Applied to extensive air showers, simulated with CORSIKA–CoREAS, it produces images that preserve key physical properties such as arrival direction and shower morphology. Notably, gamma- and hadron-induced showers exhibit distinct image structures, closely resembling those known from Cherenkov telescopes.

Furthermore, frequency-dependent imaging provides sensitivity to shower geometry, highlighting the potential of multi-band observations. Our results demonstrate the feasibility of radio-based imaging of air showers and establish a proof of principle for imaging atmospheric radio telescopes under idealized conditions.

We will present our simulation, discuss characteristic image features of air showers, and outline next steps towards incorporating detector effects and realistic noise.

Speaker: Anne Timmermans (Max-Planck-Institut für Kernphysik)

42 Radio Detection of Earth-Skimming Tau Neutrinos: A Comparison of Frequency Bands and Antenna Designs

We present a simulation study of radio detection of Earth-skimming tau neutrinos produced by tau leptons
emerging from mountain ranges. Using CoREAS simulations of nearly horizontal extensive air showers, we
investigate the radio emission characteristics and effective detection areas across multiple frequency bands,
ranging from 30 - 80 MHz to the C-band at 3.4 - 4.2 GHz. Each frequency band implies distinct antenna designs
with different noise temperatures and beam patterns, and we study the optimal choice for maximizing detection
efficiency of tau neutrino-induced air showers. The signal amplitude profiles as a function of the distance and
viewing angle relative to Xmax are compared across bands, and trigger thresholds are derived from realistic
noise temperature estimates. The resulting neutrino flux sensitivities are compared for different bandwidth and
antenna choices, providing guidance for the design of future radio detector arrays targeting the PeV - EeV tau
neutrino flux.

Speaker: Felix Schlüter (Free University Brussels (ULB))

43 The case for studying anomalous showers with the Square Kilometre Array

High-energy hadronic interactions are an important source of uncertainty in studies of the mass composition of cosmic rays. To make progress we either need to better constrain hadronic interaction parameters or find model-independent mass-sensitive parameters. Both of these options can be pursued by studying anomalous air showers in which one or more secondary hadrons carry a significant fraction of the energy and travel an exceptionally large distance before interacting. For a double-bump shower, this distance is so large that the longitudinal profile will have a secondary maximum. When the two components are closer together, the profile can be described by a single Gaisser-Hillas function, but only by using extreme values for the fit parameters. These stretched showers have a significantly longer tail than most other showers. Identification and reconstruction of anomalous showers requires very accurate observations and will for the first time be possible with the low frequency component of the Square Kilometre Array.

In this contribution, we explore the relation between the shapes of the longitudinal profiles of anomalous showers and the underlying hadronic interactions. We demonstrate how observable characteristics of these profiles can be used to test hadronic interaction models and how they can be used to make mode-independent inferences about the mass composition. Finally, we show what reconstruction resolution and total observation time we require from SKA-Low to reach these goals.

Speaker: Stijn Buitink (VUB)

44 Millisecond radio signal generation enabling simulation-based multi-parameter reconstruction of ultra-high-energy cosmic rays

In recent years, radio detection of ultra-high-energy cosmic rays (UHECRs), with energies above 1018 eV, has become an established technique. Radio emissions can be simulated with high accuracy using Monte Carlo codes such as ZHAireS and CoREAS, but these simulations are computationally intensive.
In this work, we present a machine-learning-based emulator that reproduces radio signal simulations with high accuracy in milliseconds rather than hours. Using this emulator as a neural likelihood estimator, primary particle properties are inferred via simulation-based inference. On ZHAireS simulations for the GRANDProto300 array, the method achieves an 8.9% resolution on electromagnetic energy and a 0.08° angular resolution with calibrated uncertainties, matching state-of-the-art reconstruction performance.
Finally, we deploy the method on real data, successfully reconstructing cosmic-ray candidates detected by the GP300 prototype.

Speaker: Arsène Ferrière (CEA-LIST, LPNHE)

45 Radio emission from particle distributions in extensive air showers

Radio emission simulation from particles showers is one of the most intense CPU processes in ultra high energy astroparticle physics. A detailed study of particle distributions in air showers together with their implications for radio emission will be shown. Based on the results from these studies, a new cost-effective calculation of radio emission from particle distributions will be presented and compared to results from full simulations. Lastly, we will discuss the limitations of the model and its potential applications for reconstructing extensive air showers.

Speaker: Juan Ammerman-Yebra (Radboud University)

46 Efficient Time-Domain Modeling of Geomagnetic and Askaryan Radiation from Air Showers

We introduce a semi-analytical framework to compute coherent pulses from extensive air showers initiated by cosmic rays inspired in previous work on modeling Askaryan radiation in dense media (ARVZ model). The predictions are benchmarked against detailed Monte Carlo simulations performed with the ZHAireS package. Our method accurately reconstructs the vector potential in the time domain and, consequently, the electric field in both the time and frequency domains for arbitrary observer locations on the ground. We show that the semi-analytical approach reproduces the expected radio signal with increased precision as the zenith angle becomes larger. The technique is computationally efficient, requiring only the longitudinal profiles of the total and excess charge of the shower, along with a parameterized description of the vector potential at the location at which shower maximum is seen in the Cherenkov angle. Both inputs can be obtained from ZHAireS simulations. These results are directly applicable to the interpretation of data from current radio-based air-shower experiments, as well as to the design and optimization of future cosmic-ray and neutrino detection efforts.

Speaker: Carmen Pavon-Souto

47 Radio emission in complex media simulations with Corsika8

The CORSIKA8 simulation framework, a successor of the well-known Monte Carlo air-shower simulation CORSIKA7, is a state-of-the-art implementation and testbed for the simulation of particle cascades from air to dense media. With its modular architecture, not only standard cascade simulation is possible, but a variety of additional mechanisms can be utilized. The Radio module, as one of the integral core components, implements two methods: the \enquote{Endpoint formalism} and the \enquote{ZHS algorithm}. Recent simulation studies utilizing the common environment have demonstrated good agreement, as low as 2\%, between both methods. Comparisons with CoREAS (CORSIKA7) and ZHAireS confirm the validity of the generated results and their use as a precision tool for air-shower simulation.

This contribution highlights recent development efforts with a focus on extending capabilities beyond standard air-shower simulations. A particular highlight is the electromagnetic wave propagation through complex and inhomogeneous media, including cross-media showers, achieved through full ray tracing. In addition, there is an ongoing work to implement full electrodynamic field propagation through glacial environments with EisVogel for highly realistic simulations.

Further effort has been taken to improve the computational performance of large-scale simulations; this includes computational improvements as well as reduction and prioritization through dynamic stack-based sorting. The implementation of the ARZ method for semi-analytic treatment of radio emission in dense media, avoiding costly propagation routines, is presently tested.
The current and ongoing work in the extensible CORSIKA8 framework makes it ideally suited for future studies on radio detection of a wide variety of particle cascades.

Speaker: Dominik Baack (TU Dortmund)

10:45 AM Coffee

Simulations/Simulation Studies

48 Simulation of Deep Cosmic Rays with FAERIE framework for RNO-G

The Radio Neutrino Observatory in Greenland (RNO-G) aims to detect ultra-high-energy neutrinos via Askaryan radiation, yet in-ice cosmic-ray (CR) air shower cores produce similar radio signatures that represent a significant background. While the FAERIE framework allows for high-precision modeling of these signals, its default computational requirements, which often require beyond 3,000 CPU hours per 100 PeV shower, hinder the production of the large-scale datasets necessary for deep CR studies. This work presents an optimized simulation production that implements efficient particle-handling strategies to drastically reduce computing time. By addressing computational bottlenecks, we compress processing timelines that would have spanned years into days, turning tasks that previously required years of CPU time into a matter of hours while maintaining the integrity of the radio signal’s timing, polarization, and amplitude footprint. Validations against full-scale simulations confirm that the fundamental features of the Askaryan emission, such as the Cherenkov ring structure, remain preserved within acceptable tolerances. Ultimately, this work shows how deep cosmic ray events look like with RNO-G.

Speaker: Prof. David Seckel (University of Delaware)

49 Radar Signal Properties from Neutrino-Induced Particle Cascades

The RET experiment aims to utilise radar techniques to spot ultrahigh energy neutrinos. This is achieved by targeting ionisation trails left in the wake of in-ice neutrino-induced cascades: in an ice volume illuminated with a radar system, the trail will reflect incident radio waves, allowing the neutrino to be detected via surrounding receivers. The reflected radio forms an echo signal, from which information on the cascade and progenitor neutrino can be obtained, given a detailed understanding of the signal properties. To this end, radar signals from neutrino-induced particle cascades have been investigated with the semi-analytic MARES simulation code. In this work, we utilise an ideal detector setup to explore geometry-dependent features of the signal for the full angular phase space. We discuss properties of the resulting signals in the time and frequency domains, obtaining global descriptions of the features which can be applied to help inform future reconstruction methods and detector design.

Speaker: Isha Loudon

50 What can we learn from radio emission from ice-impacting air showers?

In-ice askaryan emission from cosmic ray air showers impacting into glacial ice has now been definitively observed. In this talk I will explore what can be measured about cosmic rays, hadronic models, Askaryan emission, and radio propagation in the interaction medium by studying this class of events in current experiments.

Speaker: Cosmin Deaconu (University of Chicago)

51 Sensitivity of the Askaryan Radio Array to Ultra-High Energy Neutrinos

The Askaryan Radio Array (ARA) is an ultra-high energy (UHE) neutrino observatory designed to detect the impulsive radio waves produced by relativistic particle cascades in the Antarctic glacial ice. ARA has five independent stations which have been taking data for over a decade. Here we present a revised calculation of ARA’s sensitivity to UHE neutrinos based on a time-dependent simulation of the array from 2013-2023. In addition to improvements to detector simulations, our revised sensitivity now includes a detailed calculation of the contribution of secondary particles to the overall array-wide sensitivity. We show that, even with only five stations, the ARA dataset is the world’s most sensitive to UHE neutrinos above about 10 EeV, demonstrating the power of large in-ice radio arrays for UHE neutrino detection. Finally, we present implications for next-generation UHE neutrino experiments, in particular IceCube-Gen2 Radio.

Speaker: Marco Muzio

52 Modelling In-Ice Secondary Cosmic Ray Cascades

Cosmic-Ray (CR) air-showers impacting a high-altitude ice sheet impart a significant fraction of energy into the ice, forming a dense cascade below the ice surface. Above PeV energies, these secondary CR cascades are the target of the RET-CR experiment, and their associated radio-Askaryan emission makes them a background source in radio-neutrino detectors, such as ARA and RNO-G. This process can be simulated with the FAERIE code package, which consists of a two-step process: First, the CORSIKA package is used to simulate the CR-induced air-shower, the output from which is then propagated into the ice with the GEANT4 framework to obtain the secondary cascade. This way, FAERIE provides an accurate description of the cascade as well as shower-to-shower fluctuation effects. However, these frameworks become computationally expensive at the higher CR energies. In this work, we explore an alternative method to generate in-ice cascade profiles, utilising the particle footprint from CORSIKA simulations at the air-ice boundary. Original modifications of standard air-shower parameterisations allow the resulting in-ice cascade to be quickly obtained. We outline the method, show a comparison to full FAERIE simulations and discuss possible future applications.

Speaker: Isha Loudon

53 Likelihood-Based Reconstruction for Radio Detector Experiments

An essential part of any analysis using radio detector data is robust and accurate reconstruction of the physical parameters governing the observed signals. However, most current reconstruction methods ignore bin-to-bin noise correlations, which limits reconstruction resolution and prevents reliable event-by-event uncertainty estimates. In this talk, we present a likelihood-based approach to reconstruction that correctly models the band-limited/correlated nature of radio detector noise. This enables correct event-by-event uncertainty estimates, improves reconstruction accuracy, and has applications in detector optimization. We demonstrate the method on simulated in-ice neutrino and cosmic-ray air-shower events. The reconstruction code is available through the open-source software NuRadioReco.

Speaker: Martin Ravn (Uppsala University)

54 Semi-analytical parametrization of in-ice radio signals from cosmic ray particle cascades

Ultra-high-energy neutrino detectors such as ARA and RNO-G rely on radio antennas deployed in ice to detect particle cascades. In this context, the in-ice radio emission from cosmic-ray-induced particle cascades constitutes both a major background and a valuable calibration source. Accurate modeling of this emission currently relies on detailed Monte Carlo simulations, such as FAERIE, which remain computationally too expensive to efficiently explore the full parameter space. In this work, we show a first step to semi-analytically parameterize the in-ice radio emission from cosmic-ray showers, based on a dense library of FAERIE simulations combined with scaling laws that capture the dependence of the signal on shower parameters. This approach enables order-of-magnitude estimates of the radio signal within seconds, making it possible to generate large simulation datasets for in-ice neutrino experiments.

Speaker: Simon Chiche (Université Libre de Bruxelles)

1:00 PM Lunch

Other: Excursion & Workshop Dinner

Thu, June 11

Reconstruction

55 Radio interferometric air shower reconstruction at the Pierre Auger Observatory

The Pierre Auger Observatory in Malargüe, Argentina, is the largest cosmic-ray observatory in the world. Recently, the Observatory got a major upgrade, called AugerPrime, which includes the addition of radio antennas to each surface detector station to measure the electromagnetic radiation emitted by air showers. This extension opens up the possibility to perform a 3D-mapping of the air shower with the use of radio interferometry. By exploiting the precise timing of the radio pulses, this technique enables the reconstruction of the arrival direction, the core and the depth of shower maximum with high precision. The method requires accurate clock synchronisation between stations and precise knowledge of their positions. The radio interferometric technique has been tested and applied to a large dataset of air showers measured by the Auger Engineering Radio Array (AERA), showing its feasibility. The next step is to expand to the full array, which requires a new setup of beacons and a differential GPS campaign. In this presentation, we will explain the radio interferometry technique, present the first results from AERA and discuss the progress towards applying it to the entire array.

Speaker: Pim van Dillen (Radboud University)

56 Radio Interferometric Reconstruction of Air Shower Parameters with the SKA-Low array

The SKA-Low is a dense, uniform radio array that will enable high-precision studies of the cosmic ray induced extensive air-showers. We are developing a near-field beam-forming or interferometric framework to reconstruct key air-shower parameters with the SKA-Low array. Currently, we focus on the interferometric reconstruction of the arrival direction, shower core position, and the depth of shower maximum ($\mathrm{X}_{\mathrm{max}}$), with the goal of extending the framework to reconstruct primary energy as well. The method has been implemented on 100 PeV air showers, simulated in CoREAS, for Proton, Helium, Carbon, Silicon and Iron primaries, at zenith angles 15° and 30° which has produced a $\mathrm{X}_{\mathrm{max}}$ resolution of 15-20 $\mathrm{g/cm}^2$. We have also obtained a fine angular resolution of 0.2° and a core resolution of 5-10 m. The interferometric framework can potentially extend the sensitivity of radio detection techniques to PeV energies. With these encouraging results, we are further investigating the dependence of the reconstruction performance on the geometry and uniformity of the sampling region, while assessing its viability as a competitive and scalable technique for low-energy air showers. Therefore, we are exploring the full potential of interferometric reconstruction framework to significantly broaden the capabilities of SKA-Low in cosmic-ray physics.

Speaker: SUBHADIP SAHA (Ph.D. scholar, IIT Kanpur)

57 A New Interferometric Reconstruction Method for Radio Neutrino Detection: Application to the Future HERON Observatory

Reconstructing ultra high energy neutrinos from radio signals is challenging in low signal to noise environments, as encountered in HERON, a next generation radio array designed to detect Earth skimming UHE neutrinos using phased stations and individual antennas in a large sparse network. HERON’s phased array provides triggers for individual antennas, where the signal to noise ratio is often below 2, making conventional reconstruction difficult.

Interferometric techniques are commonly used to overcome this challenge by enhancing weak signals through coherence across the array. However, standard interferometric reconstruction relies solely on timing information, which can lead to degeneracies in the reconstructed direction and limits the achievable angular resolution.

We present an interferometric reconstruction approach that additionally exploits the expected signal footprint across the antenna array. This combined treatment significantly improves angular resolution while reducing the impact of noise.

The method achieves an angular resolution of 0.2° under realistic conditions, even for signal to noise ratios below 0.5, and we explore its potential for extracting physical observables such as the electromagnetic energy.

Speaker: Arsène Ferrière (CEA-LIST, LPNHE)

58 A bayesian air-shower reconstruction method, applied to LOFAR data

The Low-Frequency Array (LOFAR) has successfully constrained the mass composition in the $10^{16.5}$ - $10^{18}$ eV range, capturing the transition region from galactic to extragalactic sources. Standard reconstruction methods based on matching data to CoREAS simulations achieve a state-of-the-art precision in reconstruction of the $X_\mathrm{max}$, however they are computationally expensive and do not use all available signal information. We present a new reconstruction method based on the Bayesian Information Field Theory (IFT) framework.
The method utilizes signal timing and fluence information simultaneously and achieves a precision in $X_\mathrm{max}$ of $25.4 \mathrm{g/cm}^2$ and in radiation energy of 12.4% alongside a speedup with respect to standard methods of three orders of magnitude. This method benchmarks the first simultaneous reconstruction of timing and fluence data for LOFAR. We present the method itself, an application to LOFAR data and the current state of a reconstruction on the full LOFAR1.0 data set (2012-2024).

Speaker: Karen Terveer (Friedrich-Alexander-Universität Erlangen-Nürnberg)

59 Radio Reconstruction of Inclined Air Showers with Information Field Theory

The reconstruction of inclined extensive air showers from radio measurements, even though extensively researched, still holds room for improvement. In this contribution, we will present a new method for reconstructing inclined extensive air showers from radio measurements based on Information Field Theory. This Bayesian approach is based on a full forward model of air shower radio emission from the main observables (electromagnetic energy, distance to shower maximum, arrival direction) to the electric field. As a semi-parametric model, it includes not only established parametrisations of the radio emission, but also accounts for deviations from these parametrisations using Gaussian processes. Noise from narrowband emitters is also modelled explicitly, alleviating the necessity for filtering. Tests on simulations, including measured noise and a realistic instrument response, have shown that this method reaches an energy resolution of 5%, a resolution in the distance to the shower maximum of 5%, and an angular resolution of $0.03^\circ$ in azimuth and $0.04^\circ$ in zenith. For the first time, this method combines the reconstruction of the electric field, the electromagnetic energy and the arrival direction, with a performance that ranges from competitive to exceeding that of established methods.

Speaker: Mr Simon Strähnz (Karlsruhe Institute of Technology)

60 Beyond $X_\mathrm{max}$ : Reconstructing Air Shower Profiles with Information Field Theory with SKA-Low

With over 60,000 antennas deployed within a square kilometre radius, the high antenna density of the low-frequency counterpart of the Square Kilometre Array (SKA-Low) will not only perform cosmic ray observations with unprecedented accuracy, but also has the potential to reconstruct parameters beyond the current state-of-the-art. In this work, we develop a framework to reconstruct the longitudinal profile of cosmic ray air showers using measurements from dense radio antenna arrays, in particular with SKA-Low. Our model can incorporate explicit prior knowledge about our current physical understanding of air shower physics, utilises SMIET, a fast-forward simulation framework tailored to synthesise electric field pulses from any given profile, and also includes realistic antenna models to most accurately describe the observed voltage traces in each detector. The reconstruction relies on Information Field Theory (IFT), which utilises Bayesian inference to yield various realisations of the reconstructed profile from our model. IFT enables us to extract all available information in the signal (amplitude, phase, pulse shape, relative timing), and it does not explicitly rely on CoREAS simulations, drastically reducing the required computation time for reconstruction. Through this framework, the combined information of the reconstructed shower parameters will deepen our understanding of the particle interactions within these air showers, thus aiding us in a more accurate reconstruction of the mass composition of cosmic rays.

Speaker: Keito Watanabe (Institute for Astroparticle Physics, Karlsruhe Institute of Technology)

10:30 AM Coffee

Reconstruction

61 Reconstructing Electric Current Densities of Extensive Air Showers with Information Field Theory

Extensive air showers that develop through the atmosphere emit radio signals that can be measured by ground-based antennas. The resulting time-dependent electric fields contain information about the longitudinal development of the shower.

We present a Bayesian reconstruction framework based on Information Field Theory (IFT) that aims to recover the spatio-temporal structure of the macroscopic current densities responsible for radio emission in an extensive air shower. The method combines a fast, differentiable forward model for radio emission with probabilistic inference to reconstruct high-dimensional current-density fields and approximate their posterior distributions.

We demonstrate this approach on synthetic and Monte Carlo simulated data and discuss its performance, as well as the technical challenges and limitations encountered in this reconstruction framework.

Speaker: Maximilian Straub (RWTH Aachen)

62 Bayesian imaging of cosmic-ray air showers

Imaging cosmic-ray air showers via their radio emission is gaining renewed attention with the upcoming SKA-LOW, whose dense antenna arrays will measure radio emission from air showers with unprecedented resolution. To extract information about the shower structure and, ultimately, the properties of the primary cosmic ray, we develop an imaging algorithm using Bayesian inference within the framework of Information Field Theory, implemented with NIFTy. The air shower is modeled macroscopically as relativistically moving current distributions, without assuming a fixed parametric form, whose coherent radio emission produces the observed electric field traces at the antennas. We address the inverse problem of reconstructing these current distributions directly from the measured data. The reconstructed current profiles yield shower observables, the longitudinal profile of air showers, complementing the state-of-the-art reconstruction approaches being developed in parallel. We demonstrate reconstructions on synthetic data, compare results to the true current distributions, and aim to benchmark the method against the parametric macroscopic approach of MGMR3D. The algorithm is being designed to remain tractable for the large antenna multiplicities of SKA-LOW.

Speaker: Mrinal Jetti (Max Planck Institute for Astrophysics)

63 A simulation template-based air shower reconstruction method

The SKA-Low radio telescope comprising nearly 60,000 antennas in a core region of 1 km$^2$ diameter, is currently being constructed in Australia.
With a number of antennas two orders of magnitude larger than LOFAR, it is a promising next-generation instrument for cosmic-ray detection and precision measurements, operating by the same principles as LOFAR.

To fully make use of the capabilities, the shower analysis and reconstruction methods need to be refined beyond what was used at LOFAR, and multiple avenues are being pursued to this end.
Here we present first results on a template-matching reconstruction method for air shower parameters like the depth of shower maximum $X_{\rm max}$, aiming to use the information in the complete traces of the measured signals rather than only taking their energy fluence. Matching the timings allows for coherent addition of the filtered pulse traces very similar to beamforming, increasing the signal-to-noise ratios. With so many antennas, coherent beamforming lowers the detection threshold to about 1 to 3 PeV of primary energy. This is a considerable step from roughly 50 PeV for methods based on single-antenna signals, thus opening up a new cosmic-ray energy range to be measured with radio antennas.

Speaker: Arthur Corstanje (Radboud University Nijmegen)

64 Reconstruction of anomalous air showers with SKA-Low

Anomalous showers are a special class of extensive air showers (EAS) predicted by Monte Carlo simulations. They occur when a high-energy secondary particle(s) travel(s) significantly farther compared to the other high-energy secondary particles, creating a longitudinal profile which deviates from shower universality. Anomalous showers can be subdivided into double-bump showers (longitudinal profiles with two distinct peaks) and stretched showers (elongated longitudinal profiles). So far, no experiment has been able to distinguish these anomalous showers. The unique radio footprint of anomalous showers, characterized by interference patterns in the radio signal, provides a way to reconstruct longitudinal profiles from radio observations. Firstly, we show that using a simple point source emission model allows us to reconstruct some basic parameters of the longitudinal profile. By utilising SMIET, a fast-forward simulation framework that synthesises the electric field pulse for any given longitudinal profile, we can reconstruct the profile of these anomalous showers. With its dense antenna array (60,000 antennas within $1$ km$^2$) and broad frequency range ($50-350$ MHz), the Square Kilometre Array Low (SKA-Low) will be the first experiment capable of detecting these features, offering a new opportunity to probe hadronic interactions and constrain particle cross sections at ultra-high energies.

Speaker: Vital De Henau (VUB)

65 A new method of $X_{\max}$ reconstruction via geometrical backtracking of radio signals

The current generation of radio arrays has established radio detection as a viable technique for studying cosmic-ray composition through precise $X_{\max}$ measurements. The benchmark method for $X_{\max}$ reconstruction in radio detection involves fitting measured data to Monte-Carlo simulations, but this approach is computationally expensive. Alternative methods rely on parametrizations derived from such simulations. In this contribution, we present a novel and computationally efficient method based on the geometrical backtracking of radio signals measured by a ground-based antenna array, which requires only minimal input from simulations. The signal received by each antenna is considered to have travelled perpendicular to the radio wavefront, and is traced back to the shower axis, thereby reconstructing the radio emission profile of the extensive air shower. Applying this method to simulated cosmic-ray proton and iron showers in the energy range of $10^{17}-10^{18}\,\mathrm{eV}$, we observe a strong correlation between the reconstructed radio emission profile in the $20-80$ MHz frequency band and the longitudinal profile of the shower, enabling a reliable estimation of $X_{\max}$.

Speaker: Jhansi Bhavani Vuta (Department of Astroparticle Physics, Institute of Physics of the Czech Academy of Sciences, 18200 Prague, Czech Republic.)

66 Deducing the development of air showers through measurements of their induced radio-waves

The study of cosmic ray induced air showers sheds light on the mass composition of the primary particles, as well as on particle physics at high center of mass energies. So far, the longitudinal development of air showers has been measured by fluorescence telescopes, which have limited statistics. In addition, the depth of shower maximum has been deduced indirectly from measurements of particles or radio waves on the surface. In this contribution, we demonstrate that by mapping the time dependence of the measured electric field to slant depth along the axis of the air shower, a measure of the longitudinal profile of radio-wave emission can be obtained. We will show that this field mapping profile is directly related to the longitudinal particle profile.

Speaker: Charles Timmermans

12:30 PM Lunch

Electronics/Software/Trigger

67 Science Verification Analysis for Radio Neutrino Observatory in Greenland (RNO-G): Methods and Implementation

The Radio Neutrino Observatory in Greenland (RNO-G) aims to detect ultra-high-energy (UHE) neutrinos using radio technology. The detector array is planned to consist of 35 individual stations when finished and is currently under construction. As of March 2026, eight of these stations have already been commissioned with more to follow each year. To enable an efficient and effective installation in the limited time that the team can be in Greenland, it is crucial to verify that each newly deployed or updated station performs as expected. Newly installed stations must be tested to check for potential defects or installation errors and moreover, these tests should be performed regularly during the data-taking periods, as unexpected issues can arise over time, such as environmental effects, component aging or other changes during operation, which need to be identified early. This highlights the importance of having a dedicated framework to perform these tests regularly, which led to the development of the Science Verification Analysis (SVA) for RNO-G. The SVA is being continuously improved and provides a useful approach for future radio experiments, such as IceCube-Gen2. This contribution presents the current methods of the Science Verification Analysis and discusses results from the first data of the 2026 season.

Speaker: Zeynep Su Selcuk (DESY Zeuthen)

68 The Data Acquisition System for the Radio Instrument of POEMMA Balloon with Radio (PBR)

POEMMA (Probe of Extreme Multimessenger Astrophysics) Balloon with Radio (PBR) is a balloon-borne experiment being prepared for launch in 2028 from Wanaka, New Zealand, with three key instruments: Fluorescence Camera (FC), Cherenkov Camera (CC), and a Radio Instrument (RI). This talk is focused on the RI consisting of two dual-polarized sinuous antennas with bandwidth of (60 – 500) MHz and specifically its Data Acquisition System (DAQ). The RI detects the signals from atmospheric particle cascades initiated by ultra-high-energy cosmic rays and neutrinos which are synchronously sampled by the main DAQ component – a Radio Frequency System-on-Chip (RFSoC). The radio read-out is triggered externally by the CC with an additional option for internal triggering. We also plan to have two radio transmitting channels (DAC part of the RFSoC) for the instrument calibration.

Speaker: Dr Alexander Novikov (University of Delaware)

69 Development of Readout Electronics of the IceCube-Gen2 Surface Array

The IceCube Neutrino Observatory consists of two detector components: a cubic-kilometer in-ice neutrino detector and the IceTop surface array for high-energy cosmic rays. The proposed next-generation neutrino observatory, IceCube-Gen2, will increase the in-ice instrumented volume and add an additional in-ice radio detector for high-energy neutrinos. Furthermore, it will feature an entirely new surface array comprising approximately 160 surface stations covering $8\,$km$^2$, each equipped with eight scintillators for charged particle detection and three antennas for cosmic ray radio emission to enhance the physics reach. The surface radio readout of each station will receive triggers not only from local coincidences of the scintillators, but also from signals in other IceCube and IceCube-Gen2 detectors, requiring sufficient buffer depth of several seconds.
To achieve this buffer time, while aiming at $40\,$W electrical power budget per station, an Adaptive Readout for GSps Operation (ARGO) board is developed, which uses a multi-FPGA approach with LPDDR5 memory for radio buffering. Radio front-end and scintillator readout are realized with optional daughter boards to provide an experiment-agnostic mainboard that could also be used in other air-shower experiments.
In this contribution we will present the concept of the ARGO board and its current development status.

Speaker: Frederik Schmitt (KIT (IAP))

70 Station-level neural-network trigger for radio detection of cosmic-ray air showers on FPGA

Radio detection of extensive air showers induced by ultra-high-energy cosmic rays provides crucial information on their origin, composition and energy. Radio arrays detect these events, but cosmic-ray signals are exceedingly rare compared to the overwhelming radio noise and RFI. Since storing all data is not feasible, a trigger system must decide in real time which data to record. FPGAs are a fitting option for this requirement because they provide deterministic low latency and low energy consumption. In this work, we train two AI models on measured noise traces injected with simulated cosmic-ray pulses. The trained models have been quantized with hls4ml and synthesized with Vitis HLS for multiple FPGAs. Both models achieve a latency $\lesssim 8$ $\mu s$ and can be synthesized on medium to small-sized FPGAs. The performance of the proposed neural-network trigger is compared to a threshold trigger used as a baseline. When applied to experimentally measured noisy traces, the threshold trigger fails to detect signals at a false-positive rate of $10^{-4}$. In contrast, the neural-network classifier achieves a detection efficiency of about 0.8 at the same false-positive rate. When combined with an upstream denoising network, the detection efficiency increases to about 0.9 at a false-positive rate of $10^{-4}$.
These results demonstrate that neural-network-based triggers can substantially improve detection performance for radio air-shower signals and represent a viable approach for future FPGA-based station-level triggers. We aim to deploy the models on an FPGA and validate the AI trigger with real antenna data, supported by a data-emulation framework currently under development, enabling end-to-end hardware validation.

Speaker: Vesselin Dimitrov (Center for Particle Physics Siegen, Department für Physik, Universität Siegen, Germany, and Peter Grünberg Institute - Integrated Computing Architectures (ICA | PGI-4), Forschungszentrum Jülich GmbH, Germany)

71 Enhancing the neutrino detection rate of in-ice radio detectors with neural-network-based triggers

Radio detection of neutrinos remains the most promising technique for the detection of UHE neutrinos. Construction of large-scale radio-neutrino detectors, however, is limited by logistics; thus, optimization of the detector stations is the only way to enhance the science reach of future radio detectors. Improving the trigger efficiency also for faint signals is thus crucial. A complete digital readout chain of antennas enables the implementation of the trigger in the FPGA's logic, allowing for more flexible and advanced trigger decisions based on neural networks. In a first approach, a conventional pre-trigger reduces the data rate to 10 kHz followed by a second stage CNN-based neural network reducing the trigger rate further to 1Hz. The performance can be further improved by a continuous running CNN-based neural network that directly runs on the raw data, however, requiring a more complex model to run on the FPGA. Simulation studies suggest an enhancement in the neutrino detection rate by up to a factor of two, translating into a factor-of-two improvement of most science objectives. We setup evaluation boards in the lab to quantify the operation, power consumption, background rejection, and signal efficiency. In this contribution, we present the neural network design, its simulation performance, and initial lab tests.

Speaker: René Reimann (TU Dortmund)

72 What is new in NuRadioMC: Multilayer Analytic Ray-Tracing

NuRadioMC is a framework for the simulation of ultra-high-energy neutrino detectors that measure the radio signal emitted in neutrino-induced particle cascades. It is used in different radio neutrino experiments, such as RNO-G and is partly adopted by the cosmic-ray detectors LOFAR and SKA. The software enables end-to-end simulation of all relevant components starting with the neutrino interaction, the following radio emission that arises from the Askaryan effect, the radio propagation throughout the medium, and the detailed detector response. NuRadioMC is designed to provide a flexible modular framework that can be used for various detector setups, with different modules tailored to different aspects of the simulation. For example, the simulation of the radio ray paths in ice can currently be done with a computationally demanding numerical solver or a significantly faster analytical approach that relies on the usage of a simple exponential refractive index model.

However, measurements at Summit Station show that the refractive index in the Greenlandic ice sheet is better described with a three-layer exponential model instead of a single exponential. This is particularly true for shallow depths above -100 m, where the properties of the medium are strongly influenced by snow settlements and subsequent freezing of this layer.

In this contribution, we present an extension to the analytic ray-tracing method for multilayered exponential refractive index models, where the full refractive index profile is described by a collection of different single-exponential layers. This approach also enables a realistic exponential refractive index description of the atmosphere and allows us to model signal propagation over non-smooth changes in the refractive index. This talk will present the fundamentals of the multilayered analytic ray-tracing method and highlight the performance comparison to other methods. It will also provide an overview of the recent developments and current status of NuRadioMC.

Speaker: Hannes Warnhofer (Deutsches Elektronen-Synchrotron DESY / Friedrich-Alexander-University Erlangen-Nuremberg)

3:00 PM Coffee

Reconstruction

73 Differentiable End-to-End Optimization of In-Ice Radio Neutrino Detectors

In-ice radio detection is a rapidly developing field in which detector design choices made now can have a lasting impact on the sensitivity of EeV neutrino searches. While brute-force simulation campaigns are infeasible for large design parameter spaces, differentiable programming makes it possible to compute gradients of a scientific objective with respect to detector design parameters, enabling efficient gradient-based optimization. In this contribution, we present a fully differentiable end-to-end pipeline for in-ice radio neutrino simulation, detection, and reconstruction, by combining a PyTorch-based reimplementation of core NuRadioMC components, generative machine learning, neural network surrogates, and uncertainty estimation through the Fisher information. This framework enables direct optimization of the science objectives with respect to antenna positions and orientations. We will present end-to-end optimized station designs that improve reconstruction.

Speaker: Nicolai Weitkemper (TU Dortmund University)

74 Downward ultra-high-energy neutrino detection in the air with radio antennas at ground-based observatories

Ultra-high-energy (UHE) neutrinos are unique cosmic messengers that can traverse cosmological distances unattenuated, providing direct insight into the most energetic processes in the universe. Radio detection offers significant advantages for detecting highly inclined air showers induced by UHE neutrinos, due to a larger exposure range compared to particle detectors, resulting from minimal atmospheric attenuation of radio signals combined with good reconstruction precision. Furthermore, this technique improves the reconstruction of the air-shower longitudinal development, which can be used to identify neutrinos with their first interaction far below the top of the atmosphere.

In this work, we present a method for identifying UHE neutrinos using ground-based radio antennas. A reconstruction algorithm is introduced based on the radio emission maximum ($X^{\mathrm{radio}}_{\mathrm{max}}$), which demonstrates its power in distinguishing deeply developing neutrino-induced showers from background cosmic rays. Using simulations of $\nu_e$-CC-induced air showers, we evaluate the trigger efficiency, reconstruction performance, and the resulting effective area and aperture prediction for a reference array.

Our results show that radio detection significantly enhances sensitivity to very inclined showers above 1 EeV, complementing traditional particle detectors. This technique is highly scalable and applicable to future air shower radio observatories, such as GRAND. The proposed reconstruction and identification strategy provides a pathway toward achieving the sensitivity required to detect UHE neutrinos.

Speaker: Baobiao Yue (University of Wuppertal)

75 Energy estimation of cosmic ray events recorded aboard balloon-borne experiments.

Several balloon-borne radio experiments have targeted the detection of ultra-high energy neutrinos interacting near the Earth's surface. Radio pulses produced by cosmic ray air showers constitute a relevant class of events among the recorded signals. Cosmic ray signals can be produced either by downward-going air showers, where the signal reflects off the Earth's surface before reaching the payload; or by atmosphere-skimming air showers, that reach the detector directly. In this work, we discuss an update of simulation-based energy estimation methods for reflected events, as well as an adaptation of this method to atmosphere-skimming events. The performance of the method is evaluated in different scenarios of angular resolution, primary mass and environmental noise.

Speaker: Sergio Cabana Freire (IGFAE - USC)

76 Reconstruction Methods and Detector Optimisation Techniques for the Radar Echo Telescope for Neutrinos

The Radar Echo Telescope (RET) aims to observe the cosmic neutrino flux at the highest energies (>10 PeV) using radar. Radar allows for determining the position, speed and direction of any radio-reflecting object. In-ice neutrino interactions leave a dense ionisation trail that can serve as a short-lived macroscopic radar target. Therefore, radar is a potential cost-effective radio-based approach for detecting neutrinos at high energies. Using our newly obtained insights into the radar echo signal properties in both the time domain and frequency domain, we discuss reconstruction methods and detector optimisation techniques for the future Radar Echo Telescope for Neutrinos (RET-N).

Speaker: Jannes Loonen (Vrije Universiteit Brussel)

77 Progress Toward a Sub-Threshold Search for the Radar Echo Telescope for Cosmic Rays

The Radar Echo Telescope for Cosmic Rays (RET-CR) is a pathfinder experiment for a future neutrino telescope, using cosmic rays as an in-situ test beam. The buried radar system monitors for echoes off high-energy cosmic-ray induced in-ice cascades. The RET signal and dataset is well suited to a sub-threshold analysis, with properties that can be exploited in a singular-value-decomposition and machine-learning assisted search. This work presents progress toward using these tools for a future sub-threshold analysis. As a first application, we present an analysis of background data demonstrating some of our analysis techniques.

Speaker: Curtis McLennan (University of Kansas)

Other: Closing

78 Closing Remarks

Speaker: Tim Huege (KIT)