arXiv subjects

P. Giri

Publications and source records attributed to P. Giri.

8 recordsLinked to original sources

arXiv2026

The beamformed trigger of RNO-G: its design and in-field performance

The Radio Neutrino Observatory in Greenland (RNO-G) is a neutrino detector under construction at Summit Station, with 8 out of a planned 35 stations currently deployed. We have designed and deployed a new phased array (PA) trigger based on delay-and-sum beamforming and power integration. This trigger improves detector performance by suppressing thermal noise and better targeting neutrino-induced Askaryan signals. The new PA trigger has been deployed since the 2025 season. The trigger performance has been characterized using test pulses and calibration pulsers both in the lab and in-situ, and we find across these tests a 25% average reduction in the signal-to-noise ratio (SNR) needed to trigger on signals. Simulations are shown to be representative of the detector, and simulated trigger efficiencies are within 10% of measured data. Following the in-situ trigger validation, we use data-driven trigger performance to inform simulations of the detector effective volumes. The PA trigger increases our effective volume significantly, by over a factor of 2 below 0.1 EeV and at least a factor of 1.3 at the highest energies of 100 EeV.

astro-ph.IM↗

arXiv2026

Sensitivity of the As-Built 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. Using a significantly enhanced simulation pipeline, which adds data-driven detector simulations and fully incorporates secondary particle production, we calculate the trigger-level acceptance of the entire array. We compare the resulting trigger-level sensitivity to constraints on the UHE neutrino flux from other detectors. Given its exposure from 2013 to 2023, we find that ARA achieves a world-leading sensitivity above about $10^{19}$ eV, depending on the details of the event selection used in a search. Moreover, we find that up to 13 neutrinos are predicted to have been observed in this period at trigger-level, assuming the most optimistic neutrino flux models. We show that observations of secondary particles account for up to 30\% of the total acceptance starting at $10^{19}$ eV, and we explore the potential signatures and implications of both multi-pulse (from direct and refracted pulses and/or from secondary particle interactions) and multi-station events. Finally, we comment on the implications of this study for the design of next-generation UHE neutrino experiments, in particular IceCube-Gen2 Radio.

astro-ph.HE↗

arXiv2025

Validating the performance of the Radio Neutrino Observatory in Greenland using cosmic-ray air showers

The Radio Neutrino Observatory in Greenland (RNO-G) is currently under construction with the aim to detect neutrinos with energies beyond $\sim 10\,\mathrm{PeV}$. A critical part of early detector commissioning is the study of detector characteristics and potential backgrounds, for which cosmic rays play a crucial role. In this article, we report that the number of cosmic rays detected with RNO-G's shallow antennas is consistent with expectations. We further verified the agreement in the observed cosmic-ray signal shape with expectations from simulations after careful treatment of the detector systematics. Finally, we find that the reconstructed arrival direction, energy, and polarization of the cosmic-ray candidates agrees with expectations. Throughout this study, we identified detector shortcomings that are mitigated going forward. Overall, the analysis presented here is an essential first step towards validating the detector and high-fidelity neutrino detection with RNO-G in the future.

astro-ph.HE↗

arXiv2025

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

We present the first experimental evidence for in-ice Askaryan radiation -- coherent charge-excess radio emission -- from high-energy particle cascades developing in the Antarctic ice sheet. In 208 days of data recorded with the phased-array instrument of the Askaryan Radio Array, a previous analysis has incidentally identified 13 events with impulsive radiofrequency signals originating from below the ice surface. We here present a detailed reanalysis of these events. The observed event rate, radiation arrival directions, signal shape, spectral content, and electric field polarization are consistent with in-ice Askaryan radiation from cosmic ray air shower cores impacting the ice sheet. For the brightest events, the angular radiation pattern favors an extended cascade-like emitter over a pointlike source. An origin from the geomagnetic separation of charges in cosmic ray air showers is disfavored by the arrival directions and polarization. Considering the arrival angles, timing properties, and the impulsive nature of the passing events, the event rate is inconsistent with the estimation of the combined background from thermal noise events and on-surface events at the level of $5.1\,\sigma$.

astro-ph.HE↗

arXiv2025

Radio emission from airplanes as observed with RNO-G

This paper describes how intentional and unintentional radio emission from airplanes is recorded with the Radio Neutrino Observatory Greenland (RNO-G). We characterize the received signals and define a procedure to extract a clean set of impulsive signals. These signals are highly suitable for instrument calibration, also for future experiments. A set of signals is used to probe the timing precision of RNO-G in-situ, which is found to match expectations. We also discuss the impact of these signals on the ability to detect neutrinos with RNO-G.

hep-ex↗

arXiv2025

Probing the Firn Refractive Index Profile Using Antenna Response

The Radio Neutrino Observatory-Greenland (RNO-G, at Summit Station) experiment comprises an extensive fat-dipole antenna array deployed into ice boreholes over an eventual area of approximately 35 ${\rm km}^2$. Since the RNO-G experimental sensitivity depends on the radio-frequency properties of the firn, which are known to vary laterally on sub-km distance scales and vertically on sub-meter distance scales, a technique for quickly extracting information on firn ice properties with depth ($n(z)$) during drilling and deployment is desirable. Given that a dipole's resonant wavelength is fixed by geometry, the resonant frequency $f_{res}$ (measured as an S-parameter reflection coefficient [`$S_{11}$'] minimum) scales inversely with the local refractive index, allowing a translation of a depth-dependent $S_{11}$(z) profile into $n(z)$. $S_{11}$(z) data were initially taken in August, 2024 using a dipole lowered into a newly-drilled $98\pm 1$-mm diameter, 350-m deep borehole at Summit Station, Greenland, approximately 1 km from the site of the original GISP-2 core; improved measurements were subsequently made in May, 2025. We conclude that $S_{11}$(z) data can be used to estimate \RIP, on 50 cm vertical scales, at the per-cent level of accuracy required by experiments such as RN0-G.

astro-ph.IM↗

arXiv2024

Modeling the refractive index profile n(z) of polar ice for ultra-high energy neutrino experiments

We have developed an in-situ index of refraction profile n(z) for cold polar ice, using the transit times of radio signals broadcast from an englacial transmitter to 2-5 km distant radio-frequency receivers, deployed at depths up to 200 m. For propagation through a non-uniform medium, Maxwell's equations generally admit two ray propagation solutions from a given transmitter, corresponding to a direct path (D) and a refracted or reflected path (R); the measured D vs. R timing differences (dt(D,R)) are determined by the refractive index profile. We constrain n(z) near South Pole, where the Askaryan Radio Array (ARA) neutrino observatory is located, by simulating D and R ray paths via ray tracing and comparing simulations to measured dt(D,R) values. Using previous ice density data as a proxy for n(z), we demonstrate that our data strongly favors a glaciologically-motivated three-phase densification model rather than a single exponential scale height model. Effective volume simulations for a detector of ARA station antenna depths yield a 14\% increase in neutrino sensitivity over a range of $10^{17} - 10^{21}$ eV using the three-phase model compared to a single exponential.

astro-ph.IM↗

arXiv2023

Calibration and Physics with ARA Station 1: A Unique Askaryan Radio Array Detector

The Askaryan Radio Array Station 1 (A1), the first among five autonomous stations deployed for the ARA experiment at the South Pole, is a unique ultra-high energy neutrino (UHEN) detector based on the Askaryan effect that uses Antarctic ice as the detector medium. Its 16 radio antennas (distributed across 4 strings, each with 2 Vertically Polarized (VPol), 2 Horizontally Polarized (HPol) receivers), and 2 strings of transmitting antennas (calibration pulsers, CPs), each with 1 VPol and 1 HPol channel, are deployed at depths less than 100 m within the shallow firn zone of the 2.8 km thick South Pole (SP) ice. We apply different methods to calibrate its Ice Ray Sampler second generation (IRS2) chip for timing offset and ADC-to-Voltage conversion factors using a known continuous wave input signal to the digitizer, and achieve a precision of sub-nanoseconds. We achieve better calibration for odd, compared to even samples, and also find that the HPols under-perform relative to the VPol channels. Our timing calibrated data is subsequently used to calibrate the ADC-to-Voltage conversion as well as precise antenna locations, as a precursor to vertex reconstruction. The calibrated data will then be analyzed for UHEN signals in the final step of data compression. The ability of A1 to scan the firn region of SP ice sheet will contribute greatly towards a 5-station analysis and will inform the design of the planned IceCube Gen-2 radio array.

astro-ph.IM↗