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Register a new userSearches for neutrinos from cosmic-ray interactions in the Sun using seven years of IceCube data
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Cosmic-ray interactions with the solar atmosphere are expected to produce particle showers which in turn produce neutrinos from weak decays of mesons. These solar atmospheric neutrinos (SA$ u$s) have never been observed experimentally. A detection would be an important step in understanding cosmic-ray propagation in the inner solar system and the dynamics of solar magnetic fields. SA$ u$s also represent an irreducible background to solar dark matter searches and a detection would allow precise characterization of this background. Here, we present the first experimental search based on seven years of data collected from May 2010 to May 2017 in the austral winter with the IceCube Neutrino Observatory. An unbinned likelihood analysis is performed for events reconstructed within 5 degrees of the center of the Sun. No evidence for a SA$ u$ flux is observed. After inclusion of systematic uncertainties, we set a 90% upper limit of $1.02^{+0.20}_{-0.18}cdot10^{-13}$~$mathrm{GeV^{-1}cm^{-2}s^{-1}}$ at 1 TeV.
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Low background searches for astrophysical neutrino sources anywhere in the sky can be performed using cascade events induced by neutrinos of all flavors interacting in IceCube with energies as low as ~1 TeV. Previously, we showed that even with just two years of data, the resulting sensitivity to sources in the southern sky is competitive with IceCube and ANTARES analyses using muon tracks induced by charge current muon neutrino interactions - especially if the neutrino emission follows a soft energy spectrum or originates from an extended angular region. Here, we extend that work by adding five more years of data, significantly improving the cascade angular resolution, and including tests for point-like or diffuse Galactic emission to which this dataset is particularly well-suited. For many of the signal candidates considered, this analysis is the most sensitive of any experiment. No significant clustering was observed, and thus many of the resulting constraints are the most stringent to date. In this paper we will describe the improvements introduced in this analysis and discuss our results in the context of other recent work in neutrino astronomy.
The shadowing effect of the Moon and Sun in TeV cosmic rays has been measured with high statistical significance by several experiments. Unlike particles from directions close to the Moon, however, charged particles passing by the neighborhood of the Sun are affected not only by the geomagnetic but also by the solar near- and interplanetary-magnetic field. Since the latter undergoes a well-known 11-year cycle -- during which it can become highly disordered -- the cosmic-ray shadow cast by the Sun as observed on Earth is expected to change over time. We present an update of the analysis of the cosmic-ray Moon and Sun shadows using data taken with the IceCube Neutrino Observatory. With a median energy after quality cuts of approximately $50-60,$TeV, depending on the cosmic-ray flux model used, primary cosmic rays inducing events which pass IceCubes Sun shadow filter have a comparatively high energy. While the results for the Moon shadow confirm the stability of the IceCube observatory, the results for the Sun shadow exhibit a clear variation correlating with solar activity and theoretical models of the solar magnetic field.
Observations of the time-dependent cosmic-ray Sun shadow have been proven as a valuable diagnostic for the assessment of solar magnetic field models. In this paper, seven years of IceCube data are compared to solar activity and solar magnetic field models. A quantitative comparison of solar magnetic field models with IceCube data on the event rate level is performed for the first time. Additionally, a first energy-dependent analysis is presented and compared to recent predictions. We use seven years of IceCube data for the Moon and the Sun and compare them to simulations on data rate level. The simulations are performed for the geometrical shadow hypothesis for the Moon and the Sun and for a cosmic-ray propagation model governed by the solar magnetic field for the case of the Sun. We find that a linearly decreasing relationship between Sun shadow strength and solar activity is preferred over a constant relationship at the 6.4sigma level. We test two commonly used models of the coronal magnetic field, both combined with a Parker spiral, by modeling cosmic-ray propagation in the solar magnetic field. Both models predict a weakening of the shadow in times of high solar activity as it is also visible in the data. We find tensions with the data on the order of $3sigma$ for both models, assuming only statistical uncertainties. The magnetic field model CSSS fits the data slightly better than the PFSS model. This is generally consistent with what is found previously by the Tibet AS-gamma Experiment, a deviation of the data from the two models is, however, not significant at this point. Regarding the energy dependence of the Sun shadow, we find indications that the shadowing effect increases with energy during times of high solar activity, in agreement with theoretical predictions.
The main goal of the ANTARES neutrino telescope is the identification of neutrinos from cosmic accelerators. The good visibility towards the Southern sky for neutrino energies below 100 TeV and the good angular resolution for reconstructed events make the telescope excellent to test for the presence of point-like sources, especially of Galactic origin. The median angular resolution for track-like events (mainly from $ u_{mu}$ CC interactions) is $0.4^{circ}$ while the median angular resolution for contained shower-like events (mainly from $ u_{e}$ CC and all-flavour NC interactions) is $3^{circ}$. Recently the ANTARES Collaboration published the result of the search for cosmic point-like neutrino sources using track-like and shower-like events collected during nine years of data taking. In this contribution, an update to this analysis using eleven years of data recorded between early 2007 and the end of 2017, for a total livetime of 3136 days, is presented. Moreover, the results of a search for time and space correlation between the ANTARES events and 54 IceCube tracks and those of the searches for neutrino candidates associated with the IceCube-170922A event or from the direction of the TXS 0506+056 blazar are reported.
The IceCube Neutrino Observatory has observed a diffuse flux of TeV-PeV astrophysical neutrinos at 5.7{sigma} significance from an all-flavor search. The direct detection of tau neutrinos in this flux has yet to occur. Tau neutrinos become distinguishable from other flavors in IceCube at energies above a few hundred TeV, when the cascade from the tau neutrino charged current interaction becomes resolvable from the cascade from the tau lepton decay. This paper presents results from a dedicated search for tau neutrinos with energies between 214 TeV and 72 PeV. The analysis searches for IceCube optical sensors that observe two separate pulses in a single event - one from the tau neutrino interaction, and a second from the tau decay. This is the first IceCube tau neutrino search to be more sensitive to tau neutrinos than to any other neutrino flavor. No candidate events were observed in three years of IceCube data. For the first time, a differential upper limit on astrophysical tau neutrinos is derived around the PeV energy region, which is nearly three orders of magnitude lower in energy than previous limits from dedicated tau neutrino searches.
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