Article

Characterization of the astrophysical diffuse neutrino flux using starting track events in IceCube

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Abstract

A measurement of the diffuse astrophysical neutrino spectrum is presented using IceCube data collected from 2011–2022 (10.3 years). We developed novel detection techniques to search for events with a contained vertex and exiting track induced by muon neutrinos undergoing a charged-current interaction. Searching for these starting track events allows us to not only more effectively reject atmospheric muons but also atmospheric neutrino backgrounds in the southern sky, opening a new window to the sub-100 TeV astrophysical neutrino sky. The event selection is constructed using a dynamic starting track veto and machine learning algorithms. We use this data to measure the astrophysical diffuse flux as a single power law flux (SPL) with a best-fit spectral index of γ=2.58−0.09+0.10 and per-flavor normalization of ϕper−flavorAstro=1.68−0.22+0.19×10−18×GeV−1 cm−2 s−1 sr−1 (at 100 TeV). The sensitive energy range for this dataset is 3–550 TeV under the SPL assumption. This data was also used to measure the flux under a broken power law, however we did not find any evidence of a low energy cutoff.

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... We refer to the HAKKM 2014 calculation (Honda et al. 2015) for atmospheric neutrinos and to the recent Ice-Cube measurement result with starting events (Abbasi et al. 2024) for astrophysical neutrinos. We use the effective area A eff released by IceCube (Abbasi et al. 2021) for the event rate estimation. It includes effects of the neutrino absorption by Earth due to large interaction cross sections as well as selection efficiency by the analysis, and differs for neutrino flavors and energies. ...
... This is, however, not a critical impact on our conclusion, because the background rate is much smaller than CSM neutrinos in the region of present interest as shown below. Another notice is raised about atmospheric neutrinos; the referred atmospheric flux is averaged over zenith angles and the passing fraction, or self-veto effect (Argüelles et al. 2018;Abbasi et al. 2021), which is not taken into account in the referred effective area, is not reflected in the background estimation. Note again that this treatment should not change the current scope for the same reason above. ...
... where Φ CSM-ν (E ν ) is the CSM neutrino light curve at a source [s −1 ], A eff (E ν ) is the effective area taken from Abbasi et al. (2021) [m 2 ], and d is distance to the SN. We set the analysis window as E min = 10 TeV and E max = 1000 TeV. ...
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... Despite this idea could have not been experimental explored for many years, current γ-ray and neutrino telescopes have strongly improved our knowledge about astrophysical messengers, making it possible to quantitative constrain this scenario. Firstly, many analyses have highlighted a tension between the diffuse γ-ray [7] and neutrino [8][9][10][11] fluxes, especially because of the large neutrino flux below 100 TeV, exploring the potential role of hidden CR accelerators [12][13][14][15][16][17][18][19][20][21][22] (see also [23] for other details). Furthermore, the IceCube collaboration has recently found a 4.2 σ excess above the background-only hypothesis of 72 high-energy neutrino events coming from the direction of NGC 1068, a nearby AGN [24], inferring a power-law differential neutrino flux (∼ E −3.2 ) approximately ten times higher than expected from a γ-ray transparent source, taking into account the γ-ray emission observed by the Fermi-LAT telescope from this source [25][26][27]. ...
... We then extrapolate this information to the whole Seyfert population (diffuse neutrino flux), using the X-ray luminosity function (see [47]), showing that it slightly overproduce the diffuse neutrino flux inferred by the ICeCube collaboration through the starting track sample [11] in the ∼ 1−10 TeV range. Future observations from the upcoming neutrino telescopes, such as KM3NeT [48], Baikal-GVD [49][50][51], IceCube gen 2 [52], P-ONE [53] and the TRIDENT [54] telescopes will be fundamental to unveil the role of Seyfert galaxies to the diffuse neutrino spectrum as well as the role of other astrophysical accelerators. ...
... For the source density uncertainty, we take into account the variability of all parameters reported in tables 2 and 3. For F CT , we consider a uniform distribution between [0, 1]. 2 We compare the results with the latest diffuse IceCube data (6 year cascade [9] and 10 year of starting tracks [11]) and the expected KM3NeT differential sensitivity after 10 years of full operation considering all-sky shower events [48]. We notice that if we assume that all the Seyfert galaxies have the same relation between L ν and L X as imposed by the four sources used in the statistical analysis, we overproduce the diffuse neutrino flux at ∼ 1−10 TeV. ...
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The IceCube Collaboration has recently reported compelling evidence of high-energy neutrino emission from NGC 1068, and also mild excesses for NGC 4151 and CGCG420-015, local Seyfert galaxies. This has increased the interest along neutrino emission from hot-corona surrounding the super massive black holes of Seyfert Galaxies. In this paper, we revisit phenomenological constraints on the neutrino emission from hot-coronae of Seyfert galaxies, using an assumption of sub-equipartition between cosmic-rays and magnetic energy densities. We show that not only these sources are consistent with such an assumption but also that the data point towards low values for the ratio between thermal and magnetic pressure, the so called beta plasma parameters inside Seyfert galaxies. We exploit this finding to constrain the Seyfert diffuse neutrino flux and we obtain that, in order not to overproduce neutrinos, not all the sources can be efficient neutrino emitters. In our approach (along with previous findings), Seyfert galaxies provide a negligible contribution to the diffuse neutrino spectrum above ∼ 100 TeV, allowing space for other astrophysical sources. However, future data from high-energy neutrino telescopes will be crucial to shed more light onto the contribution of this source class to the cosmic neutrino background.
... One of the main goals of the IceCube observatory is the observation and description of ultrahigh-energy astrophysical neutrinos. Since the beginning of its operation, the associated neutrino flux have been constrained in different analyses, considering new data and distinct topologies [1][2][3][4][5]. These analyses are strongly motivated by our lack of knowledge about the origin and propagation of neutrinos, and by the fact that they can even be a powerful tool for searching for beyond the standard model physics [6]. ...
... In order to quantify the importance of tracks coming from subdominant channels, in Fig. 5 (left panel) we present the number of tracks events expected in the IceCube Observatory considering a period of 7.5 years, as a function of the electromagnetic equivalent deposited energy. In this calculation, we have assumed γ ¼ 2.38 and Φ 0 ¼ 1.51 in the astrophysical neutrino flux, which is the best fit for the last analysis of tracks in the IceCube Observatory [3]. The number of events is dominated by muon neutrino interactions, except at the peak of the Glashow resonance. ...
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Tracks events at the IceCube Observatory are characterized by an energetic muon crossing several kilometers before decaying. Such muons are dominantly produced in charged current (CC) muon neutrino-hadron interactions. However, muons are also produced through W -boson production and in the decay of tau leptons and heavy mesons created in neutral and charged current interactions induced by all neutrino flavors. In this paper, we investigate the contribution of these subleading channels to events characterized as tracks at the IceCube. Our results indicate that these channels correspond to a non-negligible fraction of the high-energy starting events track events. In addition, we show that its contributions are concentrated in muons that are less energetic than those arising from muonic neutrino CC interactions for the same visible energies of the process. Finally, we investigate the impact of these additional channels on the description of the astrophysical neutrino flux, and we find that the inclusion of these subleading processes are important in determining the parameters of the astrophysical neutrino flux. Published by the American Physical Society 2024
... IceCube has been continuously operating for 13 years and found the celestial neutrinos generally follow simple power laws with several selection criteria, equally distributed among flavors, as seen in Figure 1. The measurements with various analyses, such as high energy starting events [10], through-going muon tracks [11], cascades [12] and enhanced starting track event selection [13] are shown. These independent measurements are compatible with each other with spectral index ∼ 2.4 -2.9. ...
... Moreover, neutrino observation can provide hints on fundamental physics like dark matter and neutrino physics and investigate the fields of marine and Earth sciences. [11,13,28,29]. The blue band shows the best-fitting result of the π 0 model for Galactic plane [17]. ...
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Over the past ten years, several breakthroughs have been made in multi-messenger astronomy. Thanks to the IceCube Neutrino Observatory, the detection of astrophysical neutrinos was proved to be practical. However, no source has been significantly identified due to the lack of statistics and uncovered field of view. The next generation of high-energy neutrino telescope is in high demand. We propose the NEutrino Observatory in the Nanhai (NEON), located in the South China Sea to be complementary for the global neutrino detectors. This proposal describes the design and layout of the array and reports on comprehensive simulations conducted to assess its performance. The NEON project, with a volume of 10 km3^3, achieves an angular resolution of 0.1^\circ at 100 TeV. With 10 years of operation, the project's 5σ\sigma sensitivity is estimated as E2Φ2×1010E^2\Phi \sim 2 \times 10^{-10} GeV cm2^{-2} s1^{-1} for a source spectrum index of -2. We found that the variation in depth from 1700 to 3500 meters does not significantly influence the sensitivity to steady sources.
... IceCube routinely detects high-energy astrophysical neutrinos (HEANs) with TeV-PeV energies that follow a power law flux spectrum with spectral index γ = 2.53 [1]. Explanations for the source of this flux have ranged from gamma-ray bursts [2][3][4][5][6][7][8], FR0 quasars [9], blazars [10][11][12], radio-bright AGN [13][14][15], choked jet supernovae [16,17], pulsar wind nebulae [18], and more. ...
... Fiducial values are chosen so that they are not ruled out by HEAN spectra observations. served HEAN spectrum as a power law with spectral index γ = 2.53 [1], ...
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... In 2013, the IceCube neutrino telescope-the largest in operation-discovered TeV-PeV astrophysical neutrinos [55,56]. Today, IceCube continues to observe them regularly [57][58][59], and neutrino telescopes Baikal-GVD [60,61] and KM3NeT [62], currently under construction, (and ANTARES [63], now decommissioned) have reported hints of detection. Still, the origin of the bulk of high-energy astrophysical neutrinos detected remains unknown [64]. ...
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... From Fig. 8 of Ref. [51], the corresponding coupling ruled out by the IceCube (Refs. [52][53][54][55]) is above 0.6 − 1.0 in 0.5−1 TeV leptoquark mass range, while the low-energy experiments ruled out the couplings above 0.2 for M U 1 = 500 GeV and above 0.8 for M U 1 = 2500 GeV. Note that the strongest bound from the LHC search is due to pair production, which is independent of the Yukawa couplings as long as they are not extremely small as the current search is based on prompt decays of the leptoquarks [56,57]. ...
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A Correction to this paper has been published: https://doi.org/10.1038/s41586-021-03450-1.
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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=1.66−0.27+0.25 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 ≥3σ 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.
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We describe an improved in-situ calibration of the single-photoelectron charge distributions for each of the in-ice Hamamatsu Photonics R7081-02[MOD] photomultiplier tubes in the IceCube Neutrino Observatory. The characterization of the individual PMT charge distributions is important for PMT calibration, data and Monte Carlo simulation agreement, and understanding the effect of hardware differences within the detector. We discuss the single photoelectron identification procedure and how we extract the single-photoelectron charge distribution using a deconvolution of the multiple-photoelectron charge distribution.
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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.
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Tree boosting is a highly effective and widely used machine learning method. In this paper, we describe a scalable end-to-end tree boosting system called XGBoost, which is used widely by data scientists to achieve state-of-the-art results on many machine learning challenges. We propose a novel sparsity-aware algorithm for sparse data and weighted quantile sketch for approximate tree learning. More importantly, we provide insights on cache access patterns, data compression and sharding to build a scalable tree boosting system. By combining these insights, XGBoost scales beyond billions of examples using far fewer resources than existing systems.
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We consider limits on the local (z=0) density (n0n_0) of extragalactic neutrino sources set by the nondetection of steady high-energy neutrino sources producing 30\gtrsim30 TeV muon multiplets in the present IceCube data, taking into account the redshift evolution, luminosity function and neutrino spectrum of the sources. We show that the lower limit depends weakly on source spectra and strongly on redshift evolution. We find n0107 Mpc3n_0\gtrsim{10}^{-7}~{\rm Mpc}^{-3} for standard candle sources evolving rapidly, ns(1+z)3n_s\propto{(1+z)}^3, and n0105 Mpc3n_0\gtrsim{10}^{-5}~{\rm Mpc}^{-3} for nonevolving sources. The corresponding upper limits on their neutrino luminosity are Lνμeff1042 erg s1L_{{\nu_\mu}}^{\rm eff}\lesssim10^{42}~{\rm erg}~{\rm s}^{-1} and Lνμeff1041 erg s1L_{{\nu_\mu}}^{\rm eff}\lesssim10^{41}~{\rm erg}~{\rm s}^{-1}, respectively. Applying these results to a wide range of classes of potential sources, we show that powerful blazar jets associated with active galactic nuclei are unlikely to be the dominant sources. For almost all other steady candidate source classes (including starbursts, radio galaxies, and galaxy clusters and groups), an order of magnitude increase in the detector sensitivity at 0.11\sim0.1-1 PeV will enable a detection (as point sources) of the few brightest objects. Such an increase, which may be provided by next-generation detectors like IceCube-Gen2 and an upgraded KM3NET, can improve the limit on n0n_0 by more than two orders of magnitude. Future gamma-ray observations (by Fermi, HAWC and CTA) will play a key role in confirming the association of the neutrinos with their sources.
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The IceCube neutrino observatory in operation at the South Pole, Antarctica, comprises three distinct components: a large buried array for ultrahigh energy neutrino detection, a surface air shower array, and a new buried component called DeepCore. DeepCore was designed to lower the IceCube neutrino energy threshold by over an order of magnitude, to energies as low as about 10 GeV. DeepCore is situated primarily 2100 m below the surface of the icecap at the South Pole, at the bottom center of the existing IceCube array, and began taking physics data in May 2010. Its location takes advantage of the exceptionally clear ice at those depths and allows it to use the surrounding IceCube detector as a highly efficient active veto against the principal background of downward-going muons produced in cosmic-ray air showers. DeepCore has a module density roughly five times higher than that of the standard IceCube array, and uses photomultiplier tubes with a new photocathode featuring a quantum efficiency about 35% higher than standard IceCube PMTs. Taken together, these features of DeepCore will increase IceCube's sensitivity to neutrinos from WIMP dark matter annihilations, atmospheric neutrino oscillations, galactic supernova neutrinos, and point sources of neutrinos in the northern and southern skies. In this paper we describe the design and initial performance of DeepCore. (c) 2012 Elsevier B.V. All rights reserved.
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The hypothesis of an unstable charged boson to mediate muon decay radically affects the cross section for the process \overline{\nu{}}+e\rightarrow{}\overline{\nu{}}+{\mu{}}^{-{}} near the energy at which the intermediary may be produced. If the boson is assumed to have K-meson mass, the resonance occurs at an incident antineutrino energy of \sim{}2\ifmmode\times\else\texttimes\fi{}1012{10}^{12} ev. The flux of energetic antineutrinos produced in association with cosmic-ray muons will then produce two muon counts per day per square meter of detector, independently of the depth and the orientation at which the experiment is performed.
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The Fisher information matrix summarizes the amount of information in the data relative to the quantities of interest. There are many applications of the information matrix in modeling, systems analysis, and estimation, including confidence region calculation, input design, prediction bounds, and “noninformative” priors for Bayesian analysis. This article reviews some basic principles associated with the information matrix, presents a resampling-based method for computing the information matrix together with some new theory related to efficient implementation, and presents some numerical results. The resampling-based method relies on an efficient technique for estimating the Hessian matrix, introduced as part of the adaptive (“second-order”) form of the simultaneous perturbation stochastic approximation (SPSA) optimization algorithm.
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Neutrino telescopes such as IceCube search for an excess of high energy neutrinos above the steeply falling atmospheric background as one approach to finding extraterrestrial neutrinos. For samples of events selected to start in the detector, the atmospheric background can be reduced to the extent that a neutrino interaction inside the fiducial volume is accompanied by a detectable muon from the same cosmic-ray cascade in which the neutrino was produced. Here we provide an approximate calculation of the veto probability as a function of neutrino energy and zenith angle.
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The IceCube project has transformed 1 km3 of deep natural Antarctic ice into a Cherenkov detector. Muon neutrinos are detected and their direction is inferred by mapping the light produced by the secondary muon track inside the volume instrumented with photomultipliers. Reconstructing the muon track from the observed light is challenging due to noise, light scattering in the ice medium, and the possibility of simultaneously having multiple muons inside the detector, resulting from the large flux of cosmic ray muons. This paper describes work on two problems: (1) the track reconstruction problem, in which, given a set of observations, the goal is to recover the track of a muon; and (2) the coincident event problem, which is to determine how many muons are active in the detector during a time window. Rather than solving these problems by developing more complex physical models that are applied at later stages of the analysis, our approach is to augment the detector's early reconstruction with data filters and robust statistical techniques. These can be implemented at the level of on-line reconstruction and, therefore, improve all subsequent reconstructions. Using the metric of median angular resolution, a standard metric for track reconstruction, we improve the accuracy in the initial reconstruction direction by 13%. We also present improvements in measuring the number of muons in coincident events: we can accurately determine the number of muons 98% of the time.
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Random forests are a combination of tree predictors such that each tree depends on the values of a random vector sampled independently and with the same distribution for all trees in the forest. The generalization error for forests converges a.s. to a limit as the number of trees in the forest becomes large. The generalization error of a forest of tree classifiers depends on the strength of the individual trees in the forest and the correlation between them. Using a random selection of features to split each node yields error rates that compare favorably to Adaboost (Y. Freund & R. Schapire, Machine Learning: Proceedings of the Thirteenth International conference, ***, 148–156), but are more robust with respect to noise. Internal estimates monitor error, strength, and correlation and these are used to show the response to increasing the number of features used in the splitting. Internal estimates are also used to measure variable importance. These ideas are also applicable to regression.