arXiv subjects

I. Kravchenko

Publications and source records attributed to I. Kravchenko.

At least 37 records · Page 2Linked to original sources

arXiv2019

The Next-Generation Radio Neutrino Observatory -- Multi-Messenger Neutrino Astrophysics at Extreme Energies

RNO is the mid-scale discovery instrument designed to make the first observation of neutrinos from the cosmos at extreme energies, with sensitivity well beyond current instrument capabilities. This new observatory will be the largest ground-based neutrino telescope to date, enabling the measurement of neutrinos above $10^{16}$ eV, determining the nature of the astrophysical neutrino flux that has been measured by IceCube at higher energies, similarly extending the reach of multi-messenger astrophysics to the highest energies, and enabling investigations of fundamental physics at energies unreachable by particle accelerators on Earth.

astro-ph.HE↗

arXiv2019

Recent Results from The Askaryan Radio Array

The Askaryan Radio Array (ARA) is an ultra-high energy (UHE) neutrino telescope at the South Pole consisting of an array of radio antennas aimed at detecting the Askaryan radiation produced by neutrino interactions in the ice. Currently, the experiment has five stations in operation that have been deployed in stages since 2012. This contribution focuses on the development of a search for a diffuse flux of neutrinos in two ARA stations (A2 and A3) from 2013-2016. A background of $\sim 0.01-0.02$ events is expected in one station in each of two search channels in horizontal- and vertical-polarizations. The expected new constraints on the flux of ultra-high energy neutrinos based on four years of analysis with two stations improve on the previous limits set by ARA by a factor of about two. The projected sensitivity of ARA's five-station dataset is beginning to be competitive with other neutrino telescopes at high energies near $10^{10.5}\,$GeV.

astro-ph.HE↗

arXiv2019

Measurement of the real dielectric permittivity epsilon_r of glacial ice

Using data collected by the Askaryan Radio Array (ARA) experiment at the South Pole, we have used long-baseline propagation of radio-frequency signals to extract information on the radio-frequency index-of-refraction in South Polar ice. Owing to the increasing ice density over the upper 150--200 meters, rays are observed along two, nearly parallel paths, one of which is direct and a second which refracts through an inflection point, with differences in both arrival time and arrival angle that can be used to constrain the neutrino properties. We also observe indications, for the first time, of radio-frequency ice birefringence for signals propagating along predominantly horizontal trajectories, corresponding to an asymmetry of order 0.1% between the ordinary and extra-ordinary paths, numerically compatible with previous measurements of birefringent asymmetries for vertically-propagating radio-frequency signals at South Pole. Taken together, these effects offer the possibility of redundantly measuring the range from receiver to a neutrino interaction in Antarctic ice, if receiver antennas are deployed at shallow (25 m<z<100 m) depths. Such range information is essential in determining both the neutrino energy, as well as the incident neutrino direction.

astro-ph.IM↗

arXiv2018

Design and Performance of an Interferometric Trigger Array for Radio Detection of High-Energy Neutrinos

Ultra-high energy neutrinos are detectable through impulsive radio signals generated through interactions in dense media, such as ice. Subsurface in-ice radio arrays are a promising way to advance the observation and measurement of astrophysical high-energy neutrinos with energies above those discovered by the IceCube detector ($\geq$1 PeV) as well as cosmogenic neutrinos created in the GZK process ($\geq$100 PeV). Here we describe the $\textit{NuPhase}$ detector, which is a compact receiving array of low-gain antennas deployed 185 m deep in glacial ice near the South Pole. Signals from the antennas are digitized and coherently summed into multiple beams to form a low-threshold interferometric phased array trigger for radio impulses. The NuPhase detector was installed at an Askaryan Radio Array (ARA) station during the 2017/18 Austral summer season. $\textit{In situ}$ measurements with an impulsive, point-source calibration instrument show a 50% trigger efficiency on impulses with voltage signal-to-noise ratios (SNR) of $\le$2.0, a factor of $\sim$1.8 improvement in SNR over the standard ARA combinatoric trigger. Hardware-level simulations, validated with $\textit{in situ}$ measurements, predict a trigger threshold of an SNR as low as 1.6 for neutrino interactions that are in the far field of the array. With the already-achieved NuPhase trigger performance included in ARASim, a detector simulation for the ARA experiment, we find the trigger-level effective detector volume is increased by a factor of 1.8 at neutrino energies between 10 and 100 PeV compared to the currently used ARA combinatoric trigger. We also discuss an achievable near term path toward lowering the trigger threshold further to an SNR of 1.0, which would increase the effective single-station volume by more than a factor of 3 in the same range of neutrino energies.

astro-ph.IM↗

arXiv2018

Observation of classically `forbidden' electromagnetic wave propagation and implications for neutrino detection

Ongoing experimental efforts in Antarctica seek to detect ultra-high energy neutrinos by measurement of radio-frequency (RF) Askaryan radiation generated by the collision of a neutrino with an ice molecule. An array of RF antennas, deployed either in-ice or in-air, is used to infer the properties of the neutrino. To evaluate their experimental sensitivity, such experiments require a refractive index model for ray tracing radio-wave trajectories from a putative in-ice neutrino interaction point to the receiving antennas; this gives the degree of signal absorption or ray bending from source to receiver. The gradient in the density profile over the upper 200 meters of Antarctic ice, coupled with Fermat's least-time principle, implies ray "bending" and the existence of "forbidden" zones for predominantly horizontal signal propagation at shallow depths. After re-deriving the formulas describing such shadowing, we report on experimental results that, somewhat unexpectedly, demonstrate the existence of electromagnetic wave transport modes from nominally shadowed regions. The fact that this shadow-signal propagation is observed both at South Pole and the Ross Ice Shelf in Antarctica suggests that the effect may be a generic property of polar ice, with potentially important implications for experiments seeking to detect neutrinos.

astro-ph.IM↗

arXiv2018

Observation of Reconstructable Radio Emission Coincident with an X-Class Solar Flare in the Askaryan Radio Array Prototype Station

The Askaryan Radio Array (ARA) reports an observation of radio emission coincident with the "Valentine's Day" solar flare on Feb. 15$^{\rm{th}}$, 2011 in the prototype "Testbed" station. We find $\sim2000$ events that passed our neutrino search criteria during the 70 minute period of the flare, all of which reconstruct to the location of the sun. A signal analysis of the events reveals them to be consistent with that of bright thermal noise correlated across antennas. This is the first natural source of radio emission reported by ARA that is tightly reconstructable on an event-by-event basis. The observation is also the first for ARA to point radio from individual events to an extraterrestrial source on the sky. We comment on how the solar flares, coupled with improved systematic uncertainties in reconstruction algorithms, could aid in a mapping of any above-ice radio emission, such as that from cosmic-ray air showers, to astronomical locations on the sky.

astro-ph.HE↗

arXiv2017

Constraints on the Ultra-High Energy Neutrino Flux from Gamma-Ray Bursts from a Prototype Station of the Askaryan Radio Array

We report on a search for ultra-high-energy (UHE) neutrinos from gamma-ray bursts (GRBs) in the data set collected by the Testbed station of the Askaryan Radio Array (ARA) in 2011 and 2012. From 57 selected GRBs, we observed no events that survive our cuts, which is consistent with 0.12 expected background events. Using NeuCosmA as a numerical GRB reference emission model, we estimate upper limits on the prompt UHE GRB neutrino fluence and quasi-diffuse flux from $10^{7}$ to $10^{10}$ GeV. This is the first limit on the prompt UHE GRB neutrino quasi-diffuse flux above $10^{7}$ GeV.

astro-ph.HE↗

arXiv2016

Performance of two Askaryan Radio Array stations and first results in the search for ultra-high energy neutrinos

Ultra-high energy neutrinos are interesting messenger particles since, if detected, they can transmit exclusive information about ultra-high energy processes in the Universe. These particles, with energies above $10^{16}\mathrm{eV}$, interact very rarely. Therefore, detectors that instrument several gigatons of matter are needed to discover them. The ARA detector is currently being constructed at South Pole. It is designed to use the Askaryan effect, the emission of radio waves from neutrino-induced cascades in the South Pole ice, to detect neutrino interactions at very high energies. With antennas distributed among 37 widely-separated stations in the ice, such interactions can be observed in a volume of several hundred cubic kilometers. Currently 3 deep ARA stations are deployed in the ice of which two have been taking data since the beginning of the year 2013. In this publication, the ARA detector "as-built" and calibrations are described. Furthermore, the data reduction methods used to distinguish the rare radio signals from overwhelming backgrounds of thermal and anthropogenic origin are presented. Using data from only two stations over a short exposure time of 10 months, a neutrino flux limit of $3 \cdot 10^{-6} \mathrm{GeV} / (\mathrm{cm^2 \ s \ sr})$ is calculated for a particle energy of 10^{18}eV, which offers promise for the full ARA detector.

astro-ph.HE↗

arXiv2015

First Constraints on the Ultra-High Energy Neutrino Flux from a Prototype Station of the Askaryan Radio Array

The Askaryan Radio Array (ARA) is an ultra-high energy ($>10^{17}$ eV) cosmic neutrino detector in phased construction near the South Pole. ARA searches for radio Cherenkov emission from particle cascades induced by neutrino interactions in the ice using radio frequency antennas ($\sim150-800$ MHz) deployed at a design depth of 200 m in the Antarctic ice. A prototype ARA Testbed station was deployed at $\sim30$ m depth in the 2010-2011 season and the first three full ARA stations were deployed in the 2011-2012 and 2012-2013 seasons. We present the first neutrino search with ARA using data taken in 2011 and 2012 with the ARA Testbed and the resulting constraints on the neutrino flux from $10^{17}-10^{21}$ eV.

astro-ph.HE↗

arXiv2008

Relativistic Magnetic Monopole Flux Constraints from RICE

We report an upper limit on the flux of relativistic monopoles based on the non-observation of in-ice showers by the Radio Ice Cherenkov Experiment (RICE) at the South Pole. We obtain a 95% C.L. limit of order 10^{-18}/(cm^2-s-sr) for intermediate mass monopoles of 10^7<gamma<10^{12} at the anticipated energy E=10^{16} GeV. This bound is over an order of magnitude stronger than all previously published experimental limits for this range of boost parameters gamma, and exceeds two orders of magnitude improvement over most of the range. We review the physics of radio detection, describe a Monte Carlo simulation including continuous and stochastic energy losses, and compare to previous experimental limits.

astro-ph↗

arXiv2007

Search for Higgs decays to tau lepton pairs at the Tevatron

We present a search for neutral supersymmetric Higgs bosons decaying to tau+tau- pairs produced in ppbar collisions at sqrt{s}=1.96 TeV. The data have been collected with the CDF II and D0 detectors at the Tevatron collider at Fermilab (1 fb^-1 of integrated luminosity per experiment). No significant excess above the standard model backgrounds is observed. We set exclusion limits on the Higgs production cross-section times the branching fraction of its decay to tau+tau- pairs for Higgs masses in the range from 90 to 250 GeV/c^2. We also set exclusion limits on MSSM parameters m_A and tan_beta in several benchmark scenarios.

hep-ex↗

arXiv2007

Event Reconstruction and Data Acquisition for the RICE Experiment at the South Pole

The RICE experiment seeks to measure ultra-high energy neutrinos (E(nu)>10 PeV) by detection of the radio wavelength Cherenkov radiation produced by neutrino-ice collisions within Antarctic ice. An array of 16 dipole antennas, buried at depths of 100-400 m, and sensitive over the 100-500 MHz frequency range, has been continuously taking data for the last seven years. We herein describe the design and performance of the RICE experiment's event trigger and data acquisition system, highlighting elements not covered as extensively in previous publications.

astro-ph↗

arXiv2006

B Spectroscopy at Tevatron

Recent results on heavy flavor spectroscopy from the CDF and D0 experiments are reported in this contribution. Using up to 1 fb-1 of accumulated luminosity per experiment, properties of X(3872), excited B** states, and the B_c meson are measured. Also included are measurements of production rates for ground state b hadrons in ppbar collisions.

hep-ex↗

arXiv2006

RICE Limits on the Diffuse Ultra-High Energy Neutrino Flux

We present new limits on ultra-high energy neutrino fluxes above 100 PeV based on data collected by the Radio Ice Cherenkov Experiment (RICE) at the South Pole from 1999-2005. We discuss estimation of backgrounds, calibration and data analysis algorithms (both on-line and off-line), procedures used for the dedicated neutrino search, and refinements in our Monte Carlo (MC) simulation, including recent in situ measurements of the complex ice dielectric constant. An enlarged data set and a more detailed study of hadronic showers results in a sensitivity improvement of more than one order of magnitude compared to our previously published results. Examination of the full RICE data set yields zero acceptable neutrino candidates, resulting in 95% confidence-level model dependent limits on the flux (E_ν)^2(dϕ/dE_ν)<10^{-6} GeV/(cm^2s~sr}) in the energy range 10^{17}< E_ν< 10^{20} eV. The new RICE results rule out the most intense flux model projections at 95% confidence level.

astro-ph↗

arXiv2003

Recent Results from the RICE Experiment at the South Pole

We present a compilation of recent results, submitted to the 2003 International Cosmic Ray Conference (Tsukuba, Japan). These include: a) Revised Monte Carlo estimates of the radiofrequency signals produced by electromagnetic showers in ice, b) an updated search for ultra-high energy (UHE) neutrinos based on detection of radio-wavelength Cherenkov radiation; such radiation results from neutrino-induced electromagnetic showers in cold Polar ice, and c) An in situ measurement of the index of refraction through the South Polar firn.

astro-ph↗

arXiv2003

The CDFII Time-Of-Flight Detector and Impact on Beauty Flavor Tagging

The new CDFII detector incorporates a Time-of-Flight detector (TOF), employing plastic scintillator bars and fine-mesh photomultipliers. Since August 2001 the TOF system has been fully instrumented and integrated into the CDFII data acquisition system. With a design goal of $100 ps$ resolution the TOF system will provide at least two standard deviations separation between $K^{\pm}$ and $π^{\pm}$ for momenta $p<1.6 GeV/c$, complementing low momentum particle identification by means of the specific ionization energy loss measured in the drift chamber. We describe the design of the TOF detector and discuss the current status of its calibration and initial performances. Finally we review the expected impact of the TOF detector in the flavor tagging of neutral $B_S$ meson.

hep-ex↗

arXiv2003

Limits on the Ultra-High Energy Electron Neutrino Flux from the RICE Experiment

Upper limits are presented on the diffuse flux of ultra-high energy $ν_e$, based on analysis of data taken by the RICE experiment during August, 2000. The RICE receiver array at South Pole monitors cold ice for radio-wavelength Cherenkov radiation resulting from neutrino-induced in-ice showers. For energies above 1 EeV, RICE is an effective detector of over 15 km$^3$ sr. Potential signal events are separated from backgrounds using vertex location, event reconstruction, and signal shape. These are the first terrestrial limits exploiting the physics of radio Cherenkov emissions from charged-current $ν_e+N\to e+N'$ interactions.

astro-ph↗

arXiv2001

Performance and Simulation of the RICE detector

The RICE experiment (Radio Ice Cherenkov Experiment) at the South Pole, co-deployed with the AMANDA experiment, seeks to detect ultra-high energy (UHE) electron neutrinos interacting in cold polar ice. Such interactions produce electromagnetic showers, which emit radio-frequency Cherenkov radiation. We describe the experimental apparatus and the procedures used to measure the neutrino flux.

astro-ph↗