arXiv subjects

Paramita Dasgupta

Publications and source records attributed to Paramita Dasgupta.

7 recordsLinked to original sources

arXiv2026

Exact spherical-wave forward model for radio reflection from stratified media and implications for the anomalous-polarity events observed by ANITA

Radio detection of ultra-high energy particles relies on the propagation and reflection of broadband radio pulses at boundaries between natural media. In the Sommerfeld--Weyl treatment, a spherical wave is decomposed into plane-wave components and their reflection from a single homogeneous interface is calculated exactly. We extend that treatment to an arbitrary number of laterally uniform spherical layers. Both the spherical-wave decomposition of the source and the spherical geometry of the boundary are retained, while the reflection and transmission coefficients of the plane-wave components are replaced by the exact characteristic-matrix coefficients of the layered medium, evaluated at the local incidence angle on the spherical boundary. When the layer contrast is removed, the formalism recovers the single-boundary result to machine precision, and it reproduces the published spherical-surface reflectivity calculation to better than $1.1\%$ at ten HiCal-2 elevation angles, with a mean deviation of $0.6\%$. We reproduce the measured HiCal-1 reflected pulses from their measured direct partners, with a best signed correlation of $0.83$ and a median of $0.70$ across $106$ pairs, of which $101$ show the expected polarity inversion. Applied to the six reported ANITA anomalous-polarity event geometries, the buried-layer refractive index required for a sign change of the reflection coefficient ranges from $1.68$ at the steepest event to $3.8$--$5.4$ at the four near-horizon events. The full waveform calculation gives no non-inverted reflected pulse at any of these angles, showing that shallow, laterally uniform firn layering does not account for the polarity of the anomalous ANITA events. Because the formalism depends only on the complex refractive index of the medium, it applies more generally to isotropic, nonmagnetic stratified media, including ice, lunar regolith, and conducting layers.

astro-ph.IM↗

arXiv2026

Methodological Synergies between Technosignature and UHE Neutrino Searches

Radio technosignature searches and radio-based ultra-high energy (UHE) neutrino experiments address different scientific questions, but share a closely related data analysis problem: identifying rare signals of unknown morphology within large datasets dominated by thermal noise and anthropogenic radio-frequency interference (RFI). UHE neutrino radio experiments (including ARA, RNO-G, ANITA, and PUEO) have developed advanced methodologies for continuous-wave (CW) mitigation and background characterization. This invited contribution makes that connection concrete through three points. First, we demonstrate that catalog-based time-domain sine subtraction -- the CW mitigation technique used in ANITA and ARA -- can be adapted for technosignature pipelines by restricting subtraction to documented persistent contaminants, improving broadband transient visibility while preserving uncataloged narrowband candidates. Second, we identify a structural equivalence between spatiotemporal clustering used in UHE neutrino experiments and direction/cadence-based RFI rejection in radio SETI, proposing a joint feature space incorporating direction, time, frequency, bandwidth, duration, and polarization. Third, we argue that background-only anomaly ranking is the natural second stage of this workflow, providing morphology-agnostic candidate triage. Together, these ideas motivate a 'preserve-then-rank' workflow for commensal rare-event discovery, opening a near-term path toward cross-community collaboration.

astro-ph.IM↗

arXiv2025

First Ultra High Energy Neutrino Search with a Hybrid Phased and Traditional Detector in the Askaryan Radio Array

The Askaryan Radio Array (ARA) is an in-ice ultrahigh energy (UHE, >10 PeV) neutrino experiment at the South Pole, designed to detect neutrino-induced radio emission in ice. It consists of five independent stations, each featuring a cubic lattice of in-ice antenna clusters spaced ~30 m apart and buried ~200 m below the surface. The fifth ARA station (A5) is unique due to its central phased array string, which employs an interferometric trigger to enhance sensitivity to weak signals otherwise buried in noise. This low-threshold trigger makes ARA the first in-ice radio neutrino experiment to demonstrate a significant improvement in detecting low signal-to-noise ratio (SNR) radio signals. We present progress toward the first UHE neutrino search utilizing A5's hybrid detection capability, incorporating advancements in data selection and background rejection. This analysis is the first to fully apply dedicated event selection to both components of ARA's hybrid detector, improving directional reconstruction and significantly enhancing background rejection compared to previous analyses. This approach paves the way for next-generation in-ice UHE neutrino experiments.

astro-ph.HE↗

arXiv2025

Ideas and Requirements for the Global Cosmic-Ray Observatory (GCOS)

After a successful kick-off meeting in 2021. two workshops in 2022 and 2023 on the future Global Cosmic-Ray Observatory (GCOS) focused mainly on a straw man design of the detector and science possibilities for astro- and particle physics. About 100 participants gathered for in-person and hybrid panel discussions. In this report, we summarize these discussions, present a preliminary straw-man design for GCOS and collect short write-ups of the flash talks given during the focus sessions.

astro-ph.IM↗

arXiv2024

A search for the ultra high energy neutrinos with the low threshold phased array trigger system of the Askaryan Radio Array

The Askaryan Radio Array (ARA) is an in-ice ultra high energy (UHE, $>10$ PeV) neutrino experiment at the South Pole that aims to detect UHE neutrino-induced radio emission in ice. ARA consists of five independent stations each consisting of a cubical lattice of in-ice antenna clusters with a side length of $\sim$10 m buried at $\sim$200 m below the ice surface. The fifth station of ARA (A5) is special as this station has an additional central string, the phased array (PA), which provides an interferometric trigger that enables ARA to trigger on weak signals that are otherwise buried in noise. Leveraging the low threshold phased array trigger, ARA was the first radio neutrino experiment to demonstrate significant improvement in sensitivity to weak signals. In this contribution, we present initial results from a neutrino search combining information from both the traditional station antennas and the phased array antennas of the A5 station. We show the improved vertex reconstruction achieved with this approach, and leveraging this improvement, we expect to enhance the analysis efficiency beyond what has been achieved previously by ARA. This analysis is the paradigmatic representation of future neutrino searches with the next generation of in-ice neutrino experiments.

astro-ph.HE↗

arXiv2023

Progress Towards a Diffuse Neutrino Search in the Full Livetime of the Askaryan Radio Array

The Askaryan Radio Array (ARA) is an in-ice ultrahigh energy (UHE, $>10$ PeV) neutrino experiment at the South Pole that aims to detect radio emissions from neutrino-induced particle cascades. ARA has five independent stations which together have collected nearly 24 station-years of data. Each of these stations search for UHE neutrinos by burying in-ice clusters of antennas $\sim 200$ m deep in a roughly cubical lattice with side length $\sim 15$ m. Additionally, the fifth ARA station (A5) has a beamforming trigger, referred to as the Phased Array (PA), consisting of a trigger array of 7 tightly packed vertically-polarized antennas. In this proceeding, we will present a neutrino search with the data of this "hybrid" station, emphasizing its capabilities for improved analysis efficiencies, background rejection, and neutrino vertex reconstruction. This is enabled by combining the closely packed trigger antennas with the long-baselines of the outrigger antennas. We will also place the A5 analysis into the context of the broader five station analysis program, including efforts to characterize and calibrate the detector, model and constrain backgrounds, and reject noise across the entire array. We anticipate this full neutrino search to set world-leading limits above 100 PeV, and inform the next generation of neutrino detection experiments.

astro-ph.HE↗

arXiv2019

General Treatment of Reflection of Spherical Electromagnetic Waves from a Spherical Surface and its Implications for the ANITA Anomalous Polarity Events

We develop a general formalism to treat reflection of spherical electromagnetic waves from a spherical surface. Our main objective is interpretation of radio wave signals produced by cosmic ray interactions with Earth's atmosphere which are observed by the Antarctica based ANITA detector after reflection off the ice surface. The incident wave is decomposed into plane waves and each plane wave is reflected off the surface using the standard Fresnel formalism. For each plane wave the reflected wave is assumed to be locally a plane wave. This is a very reasonable assumption and there are no uncontrolled approximations in our treatment of the reflection phenomenon. The surface roughness effects are also included by using a simple model. We apply our formalism to the radiation produced by the balloon-borne HiCal radio-frequency (RF) transmitter. Our final results for the reflected power are found to be in good agreement with data for all elevation angles. We also study the properties of reflected radio pulses in order to study their phase relationship with direct pulses. We find that for some roughness models the pulse shape can be somewhat distorted and may be misidentified as a direct pulse. However this is a rather small effect and is unable to provide an explanation for the observed mystery events by ANITA.

physics.class-ph↗