A number of different fits to solar neutrino mixing and mass square difference were performed using 1496 days of Super-Kamiokande-I's solar neutrino data. These data select two allowed areas at large ...neutrino mixing when combined with either the solar
8B flux prediction of the standard solar model or the SNO interaction rate measurements. A global fit combining SK data with the solar neutrino interaction rates measured by Homestake, SNO, Gallex/GNO and SAGE prefers a single allowed area, the Large Mixing Angle solution, at the 98.9% confidence level. The mass square difference
Δm
2 between the two mass eigenstates ranges from about 3 to 19×10
−5 eV
2, while the mixing angle
θ is in the range of tan
2
θ≈0.25–0.65.
We report the result of a search for neutrino oscillations using precise measurements of the recoil electron energy spectrum and zenith angle variations of the solar neutrino flux from 1258 days of ...neutrino-electron scattering data in Super-Kamiokande. The absence of significant zenith angle variation and spectrum distortion places strong constraints on neutrino mixing and mass difference in a flux-independent way. Using the Super-Kamiokande flux measurement in addition, two allowed regions at large mixing are found.
The flavor ratio of the atmospheric neutrino flux and its zenith angle dependence have been studied in the multi-GeV energy range using an exposure of 25.5 kiloton-years of the Super-Kamiokande ...detector. By comparing the data to a detailed Monte Carlo simulation, the ratio (
μ/
e)
DATA/(
μ/
e)
MC was measured to be 0.66±0.06(stat.)±0.08(sys.). In addition, a strong distortion in the shape of the
μ-like event zenith angle distribution was observed. The ratio of the number of upward to downward
μ-like events was found to be 0.52
+0.07
−0.06(stat.)±0.01(sys.), with an expected value of 0.98±0.03(stat.)±0.02(sys.), while the same ratio for the
e-like events was consistent with unity.
This Letter presents the results from pointlike neutrino source searches using ten years of IceCube data collected between April 6, 2008 and July 10, 2018. We evaluate the significance of an ...astrophysical signal from a pointlike source looking for an excess of clustered neutrino events with energies typically above ∼1 TeV among the background of atmospheric muons and neutrinos. We perform a full-sky scan, a search within a selected source catalog, a catalog population study, and three stacked Galactic catalog searches. The most significant point in the northern hemisphere from scanning the sky is coincident with the Seyfert II galaxy NGC 1068, which was included in the source catalog search. The excess at the coordinates of NGC 1068 is inconsistent with background expectations at the level of 2.9σ after accounting for statistical trials from the entire catalog. The combination of this result along with excesses observed at the coordinates of three other sources, including TXS 0506+056, suggests that, collectively, correlations with sources in the northern catalog are inconsistent with background at 3.3σ significance. The southern catalog is consistent with background. These results, all based on searches for a cumulative neutrino signal integrated over the 10 years of available data, motivate further study of these and similar sources, including time-dependent analyses, multimessenger correlations, and the possibility of stronger evidence with coming upgrades to the detector.
On 2017 August 17 a binary neutron star coalescence candidate (later designated GW170817) with merger time 12:41:04 UTC was observed through gravitational waves by the Advanced LIGO and Advanced ...Virgo detectors. The Fermi Gamma-ray Burst Monitor independently detected a gamma-ray burst (GRB 170817A) with a time delay of \(\sim 1.7\,{\rm{s}}\) with respect to the merger time. From the gravitational-wave signal, the source was initially localized to a sky region of 31 deg2 at a luminosity distance of \({40}_{-8}^{+8}\) Mpc and with component masses consistent with neutron stars. The component masses were later measured to be in the range 0.86 to 2.26 \(\,{M}_{\odot }\). An extensive observing campaign was launched across the electromagnetic spectrum leading to the discovery of a bright optical transient (SSS17a, now with the IAU identification of AT 2017gfo) in NGC 4993 (at \(\sim 40\,{\rm{Mpc}}\)) less than 11 hours after the merger by the One-Meter, Two Hemisphere (1M2H) team using the 1 m Swope Telescope. The optical transient was independently detected by multiple teams within an hour. Subsequent observations targeted the object and its environment. Early ultraviolet observations revealed a blue transient that faded within 48 hours. Optical and infrared observations showed a redward evolution over ∼10 days. Following early non-detections, X-ray and radio emission were discovered at the transient’s position \(\sim 9\) and \(\sim 16\) days, respectively, after the merger. Both the X-ray and radio emission likely arise from a physical process that is distinct from the one that generates the UV/optical/near-infrared emission. No ultra-high-energy gamma-rays and no neutrino candidates consistent with the source were found in follow-up searches. These observations support the hypothesis that GW170817 was produced by the merger of two neutron stars in NGC 4993 followed by a short gamma-ray burst (GRB 170817A) and a kilonova/macronova powered by the radioactive decay of r-process nuclei synthesized in the ejecta.
We report on the first measurement of the astrophysical neutrino flux using particle showers (cascades) in IceCube data from 2010–2015. Assuming standard oscillations, the astrophysical neutrinos in ...this dedicated cascade sample are dominated (∼90 %) by electron and tau flavors. The flux, observed in the sensitive energy range from 16 TeV to 2.6 PeV, is consistent with a single power-law model as expected from Fermi-type acceleration of high energy particles at astrophysical sources. We find the flux spectral index to be γ = 2.53 ± 0.07 and a flux normalization for each neutrino flavor of ϕastro = 1.66+0.25 −0.27 at E0 = 100 TeV , in agreement with IceCube's complementary muon neutrino results and with all-neutrino flavor fit results. In the measured energy range we reject spectral indices γ ≤ 2.28 at ≥ 3 σ significance level. Because of high neutrino energy resolution and low atmospheric neutrino backgrounds, this analysis provides the most detailed characterization of the neutrino flux at energies below ∼100 TeV compared to previous IceCube results. Results from fits assuming more complex neutrino flux models suggest a flux softening at high energies and a flux hardening at low energies (p value ≥ 0.06). The sizable and smooth flux measured below ∼100 TeV remains a puzzle. In order to not violate the isotropic diffuse gamma-ray background as measured by the Fermi Large Area Telescope, it suggests the existence of astrophysical neutrino sources characterized by dense environments which are opaque to gamma rays.
Abstract
We present a measurement of the high-energy astrophysical muon–neutrino flux with the IceCube Neutrino Observatory. The measurement uses a high-purity selection of 650k neutrino-induced muon ...tracks from the northern celestial hemisphere, corresponding to 9.5 yr of experimental data. With respect to previous publications, the measurement is improved by the increased size of the event sample and the extended model testing beyond simple power-law hypotheses. An updated treatment of systematic uncertainties and atmospheric background fluxes has been implemented based on recent models. The best-fit single power-law parameterization for the astrophysical energy spectrum results in a normalization of
ϕ
@
100
TeV
ν
μ
+
ν
¯
μ
=
1.44
−
0.26
+
0.25
×
10
−
18
GeV
−
1
cm
−
2
s
−
1
sr
−
1
and a spectral index
γ
SPL
=
2.37
−
0.09
+
0.09
, constrained in the energy range from 15 TeV to 5 PeV. The model tests include a single power law with a spectral cutoff at high energies, a log-parabola model, several source-class-specific flux predictions from the literature, and a model-independent spectral unfolding. The data are consistent with a single power-law hypothesis, however, spectra with softening above one PeV are statistically more favorable at a two-sigma level.
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