The Askaryan Radio Array (ARA) is an ultrahigh energy (UHE, > 1017 eV) neutrino detector designed to observe neutrinos by searching for the radio waves emitted by the relativistic products of ...neutrino-nucleon interactions in Antarctic ice. In this paper, we present constraints on the diffuse flux of ultrahigh energy neutrinos between 1016 and 1021 eV resulting from a search for neutrinos in two complementary analyses, both analyzing four years of data (2013–2016) from the two deep stations (A2, A3) operating at that time. We place a 90% CL upper limit on the diffuse all flavor neutrino flux at 1018 eV of EF(E) = 5.6 × 10−16 cm−2 s−1 sr−1. This analysis includes four times the exposure of the previous ARA result and represents approximately 1 / 5 th the exposure expected from operating ARA until the end of 2022.
Owing to their small interaction cross-section, neutrinos are unparalleled astronomical tracers. Ultra-high energy (UHE; E > 10 PeV) neutrinos probe the most distant, most explosive sources in the ...Universe, often obscured to optical telescopes. Radio-frequency (RF) detection of Askaryan radiation in cold polar ice is currently regarded as the best experimental measurement technique for UHE neutrinos, provided the RF properties of the ice target can be well-understood. To that end, the Askaryan Radio Array (ARA) experiment at the South Pole has used long-baseline RF propagation to extract information on the index-of-refraction (n=ϵr) in South Polar ice. Owing to the increasing ice density over the upper 150–200 m, rays are measured along two, nearly parallel paths, one of 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 (first) indications for RF ice birefringence for signals propagating along predominantly horizontal trajectories, corresponding to an asymmetry of order 0.1% between the ordinary and extra-ordinary birefringent axes, numerically compatible with previous measurements of birefringent asymmetries for vertically-propagating radio-frequency signals at South Pole. Qualitatively, 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 (z ∼ −25 m) depths. Such range information is essential in determining both the neutrino energy, as well as the incident neutrino direction.
We performed scanning tunneling microscopy/spectroscopy (STM/STS) in the stripe-ordered state of La
2−
x
−
y
Nd
y
Sr
x
CuO
4 (
x
=
1
8
,
y∼0.4) at
T∼9
K (>
T
c) and compared the results with those of ...superconducting La
2−
x
Sr
x
CuO
4 (
x
∼
1
8
). The STS spectrum of La
2−
x
−
y
Nd
y
Sr
x
CuO
4 (
x
=
1
8
,
y∼0.4) exhibits a
d-wave-like gap with broad gap-edge peaks and an asymmetrically V-shaped background. The observed gap is almost the same in magnitude and shape as that of La
2−
x
Sr
x
CuO
4 (
x
∼
1
8
). This result suggests that there is a close relation between the stripe order (or correlation) and the pseudogap formation because 2
Δ
0 scales with the pseudogap temperature in La
2−
x
Sr
x
CuO
4.
Objective: The cortical relay time (CRT) for V2 of long-latency reflexes (LLRs) in the contracted thenar and short toe flexor muscles was studied.
Methods: LLRs and somatosensory evoked potentials ...(SEPs) were studied by electrical stimulation of the median or posterior tibial nerve. The CRT for V2 was calculated by subtracting the onset latency of cortical potentials in SEPs and that of motor evoked potentials (MEPs) by transcranial magnetic stimulation (TMS) from the onset latency of V2 in eight healthy subjects.
Results: The CRT for the thenar muscles was
11.4±0.9 ms (mean±SD), as the onset latency was
48.8±1.4 ms for V2,
16.0±1.2 ms for N20 and
21.3±1.1 ms for MEP, respectively. The CRT for the short toe flexor muscles was
3.0±1.3 ms, as the onset latency was
80.5±4.5 ms for V2,
35.3±1.8 ms for P38 and
42.2±2.0 ms for MEP, respectively.
Conclusion: Significantly longer CRT for V2 for the thenar muscles (
P<0.001, paired Student's
t test) may indicate more synaptic relays as compared to that for the short toe flexor muscles.
We develop an in-situ index of refraction profile using the transit time of radio signals broadcast from an englacial transmitter to 2-5 km distant radio-frequency receivers, deployed at depths up to ...200 m. Maxwell's equations generally admit two ray propagation solutions from a given transmitter, corresponding to a direct path (D) and a refracted path (R); the measured D vs. R (dt(D,R)) timing differences provide constraints on the index of refraction profile near South Pole, where the Askaryan Radio Array (ARA) neutrino observatory is located. We constrain the refractive index profile by simulating D and R ray paths via ray tracing and comparing those to measured dt(D,R) signals. 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. Simulations show that the single exponential model overestimates ARA neutrino sensitivity compared to the three-phase model.
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.
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