High-energy Neutrino Telescope Research Articles

A Hierarchical Bayesian Approach to Point-source Analysis in High-energy Neutrino Telescopes

We propose a novel approach to the detection of point-like sources of high-energy neutrinos. Motivated by evidence for emerging sources in existing data, we focus on the characterization and interpretation of these sources rather than the rejection of the background-only hypothesis. The hierarchical Bayesian model is implemented in the Stan platform, enabling computation of the posterior distribution with a Hamiltonian Monte Carlo algorithm. We simulate a population of weak neutrino sources detected by the IceCube experiment and use the resulting data set to demonstrate and validate our framework. We show that even for the challenging case of sources at the threshold of detection and using limited prior information, it is possible to correctly infer the source properties. Additionally, we demonstrate how modeling flexible connections between similar sources can be used to recover the contribution of sources that would not be detectable individually. While a direct comparison of our method to existing approaches is challenged by the fundamental differences in frequentist and Bayesian frameworks, we draw parallels where possible. In particular, we highlight how including more complexity into the source modeling can increase the sensitivity to sources and their populations.

Towards multi-messenger observations of core-collapse supernovae harbouring choked jets

Context. Over the past decade, choked jets have attracted particular attention as potential sources of high-energy cosmic neutrinos. It is challenging to test this hypothesis because of the missing gamma-ray counterpart. An identification of other electromagnetic signatures is therefore crucial. Extended H envelopes surrounding collapsing massive stars might choke launched jets. In addition, the same progenitors are expected to produce a shock-breakout signal in the ultraviolet (UV) and optical that lasts several days. Early UV radiation in particular carries important information about the presence and nature of choked jets. Aims. While UV observations of core-collapse supernovae have so far been limited, the full potential of observations in this spectral band will soon be transformed by the ULTRASAT satellite mission with its unprecedented field of view. We investigated the detection prospects of choked jet progenitors by ULTRASAT in relation to their visibility in the optical band by the currently operating telescope ZTF. In addition, as choked jets can produce neutrinos via hadronic and photohadronic interactions in choked jets, we also investigated how neutrino observations by existing Cherenkov high-energy neutrino telescopes (e.g. IceCube and KM3NeT) can be used in association with electromagnetic signals from shock-breakout events. Methods. By considering fiducial parameters of the source population and instrument performances, we estimated the maximum redshift up to which ULTRASAT and ZTF are able to detect ultraviolet and optical signals from these explosions, respectively. Furthermore, we discuss coordinated multi-messenger observations using ULTRASAT, ZTF, and high-energy neutrino telescopes. Results. We find that ULTRASAT will double the volume of the sky that is currently visible by ZTF for the same emitting sources. This will enlarge the sample of observed Type II supernovae by ∼60%. For optimised multi-messenger detections, the delay between neutrinos produced at the shock breakout (during the jet propagation inside the stellar envelope) and ULTRASAT observations should be of ∼4 (5) days, with subsequent follow-up by instruments such as ZTF about one week later. We estimate that fewer than 1% of the core-collapse supernovae from red supergiant stars that are detectable in UV with ULTRASAT might host a choked jet and release TeV neutrinos. Electromagnetic and neutrino detections, if accompanied by additional photometric and spectroscopic follow-up with compelling evidence for a relativistic jet launched by the central engine of the source, would suggest that core-collapse supernovae harbouring choked jets are the main contributors to the diffuse astrophysical high-energy neutrino flux.

Berezinsky hidden sources: an emergent tension in the high-energy neutrino sky?

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.

STRAW-b (STRings for Absorption length in Water-b): the second pathfinder mission for the Pacific Ocean Neutrino Experiment

Since 2018, the potential for a high-energy neutrino telescope, named the Pacific Ocean Neutrino Experiment (P-ONE), has been thoroughly examined by two pathfinder missions, STRAW and STRAW-b, short for STRAW and STRAW-b. The P-ONE project seeks to install a neutrino detector with a one cubic kilometer volume in the Cascadia Basin's deep marine surroundings, situated near the western shores of Vancouver Island, Canada. To assess the environmental conditions and feasibility of constructing a neutrino detector of that scale, the pathfinder missions, STRAW and STRAW-b, have been deployed at a depth of 2.7 km within the designated site for P-ONE and were connected to the NEPTUNE observatory, operated by Ocean Networks Canada (ONC). While STRAW focused on analyzing the optical properties of water in the Cascadia Basin, STRAW-b employed cameras and spectrometers to investigate the characteristics of bioluminescence in the deep-sea environment. This report introduces the STRAW-b concept, covering its scientific objectives and the instrumentation used. Furthermore, it discusses the design considerations implemented to guarantee a secure and dependable deployment process of STRAW-b. Additionally, it showcases the data collected by battery-powered loggers, which monitored the mechanical stress on the equipment throughout the deployment. The report also offers an overview of STRAW-b's operation, with a specific emphasis on the notable advancements achieved in the data acquisition (DAQ) system and its successful integration with the server infrastructure of ONC.

Present and future constraints on flavor-dependent long-range interactions of high-energy astrophysical neutrinos

The discovery of new, flavor-dependent neutrino interactions would provide compelling evidence of physics beyond the Standard Model. We focus on interactions generated by the anomaly-free, gauged, abelian lepton-number symmetries, specifically Le – Lμ, Le – Lτ , and Lμ – Lτ , that introduce a new matter potential sourced by electrons and neutrons, potentially impacting neutrino flavor oscillations. We revisit, revamp, and improve the constraints on these interactions that can be placed via the flavor composition of the diffuse flux of high-energy astrophysical neutrinos, with TeV–PeV energies, i.e., the proportion of νe, νμ, and ντ in the flux. Because we consider mediators of these new interactions to be ultra-light, lighter than 10−10 eV, the interaction range is ultra-long, from km to Gpc, allowing vast numbers of electrons and neutrons in celestial bodies and the cosmological matter distribution to contribute to this new potential. We leverage the present-day and future sensitivity of high-energy neutrino telescopes and of oscillation experiments to estimate the constraints that could be placed on the coupling strength of these interactions. We find that, already today, the IceCube neutrino telescope demonstrates potential to constrain flavor-dependent long-range interactions significantly better than existing constraints, motivating further analysis. We also estimate the improvement in the sensitivity due to the next-generation neutrino telescopes such as IceCube-Gen2, Baikal-GVD, KM3NeT, P-ONE, and TAMBO.

IceCube and the origin of ANITA-IV events

Recently, the ANITA collaboration announced the detection of new, unsettling upgoing Ultra-High-Energy (UHE) events. Understanding their origin is pressing to ensure success of the incoming UHE neutrino program. In this work, we study their internal consistency and the implications of the lack of similar events in IceCube. We introduce a generic, simple parametrization to study the compatibility between these two observatories in Standard Model-like and Beyond Standard Model scenarios: an incoming flux of particles that interact with Earth nucleons with cross section σ, producing particle showers along with long-lived particles that decay with lifetime τ and generate a shower that explains ANITA observations. We find that the ANITA angular distribution imposes significant constraints, and when including null observations from IceCube only τ ~ 10−3–10−2 s and σ ~ 10−33– 10−32 cm2 can explain the data. This hypothesis is testable with future IceCube data. Finally, we discuss a specific model that can realize this scenario. Our analysis highlights the importance of simultaneous observations by high-energy optical neutrino telescopes and new UHE radio detectors to uncover cosmogenic neutrinos or discover new physics.

Estimating source distances for high-energy neutrinos: A method for improving electromagnetic follow-up searches

High-energy neutrino telescopes such as ICECUBEor KM3NET issue public alerts describing the characteristics of possible astrophysical high-energy neutrino events. This information, particularly with respect to the arrival direction and the associated uncertainty of the neutrino candidates, is used by observatories to search for possible electromagnetic counterparts. Such searches are complicated by the size of localisation areas, which can be up to tens of squared degrees or more, coupled with the absence of constraints on the distance or nature of the possible source – in contrast to gravitational wave alerts issued by instruments such as LIGO/VIRGO. Here, we describe a method for deriving a probable distance interval for the astrophysical source that may possibly be associated with a high-energy neutrino event, which may then be used in a cross-matching with galaxy catalogues to search for plausible electromagnetic counterparts. This study is intended to serve as a guide for high-energy neutrino followup campaigns.

Nanobeacon: A time calibration device for the KM3NeT neutrino telescope

The KM3NeT Collaboration is currently constructing a multi-site high-energy neutrino telescope in the Mediterranean Sea consisting of matrices of pressure-resistant glass spheres, each holding a set of 31 small-area photomultipliers. The main goals of the telescope are the observation of neutrino sources in the Universe and the measurement of the neutrino oscillation parameters with atmospheric neutrinos. A relative time synchronisation between photomultipliers of the nanosecond order needed to guarantee the required angular resolution of the detector. Due to the large detector volumes to be instrumented by KM3NeT, a cost reduction of the different systems is a priority. To this end, the inexpensive Nanobeacon has been designed and developed by the KM3NeT Collaboration to be used for detector time-calibration studies. At present, more than 600 Nanobeacons have been already produced. The characterisation of the optical pulse and the wavelength emission profile of the devices is critical for the time calibration. The optical pulse rise time has been quantified as less than 3 ns, while the Full Width Half Maximum is less than 6 ns. The wavelength drift, due to a variation of the supply voltage, has also been qualified as lower than 10 nm for the full range of the Nanobeacon. In this paper, more details about the main features of the Nanobeacon design, production and operation, together with the main properties of the light pulse generated are described.

Multi-detector approach to enhance the sensitivity of neutrino telescopes to low-energy astrophysical sources

While large neutrino telescopes have so far mainly focused on the detection of TeV-PeV astrophysical neutrinos, several efforts are ongoing to extend the sensitivity down to the GeV level for transient sources. Only a handful of neutrino searches have been carried out at the moment leaving the signature of astrophysical transients poorly known in this energy range. In this contribution, we discuss the motivations for high-energy neutrino telescopes to explore the GeV energy range and summarize the current limitations of detectors, such as IceCube and KM3NeT. We then present and compare different approaches for multi-detector analyses that may enhance the sensitivity to a transient GeV neutrino flux.

Sterile neutrino dark matter from generalized CPT -symmetric early-Universe cosmologies

We generalize gravitational particle production in a radiation-dominated $CPT$-symmetric universe to non-standard, but also $CPT$-symmetric early universe cosmologies. We calculate the mass of a right-handed "sterile" neutrino needed for it to be the cosmological dark matter. Since generically sterile neutrinos mix with the Standard Model active neutrinos, we use state-of-the-art tools to compute the expected spectrum of gamma rays and high-energy active neutrinos from ultra-heavy sterile neutrino dark matter decay. We demonstrate that the sterile neutrinos are never in thermal equilibrium in the early universe. We show that very high-energy Cherenkov telescopes might detect a signal for sterile neutrino lifetimes up to around 10$^{27}$ s, while a signal in high-energy neutrino telescopes such as IceCube could be detectable for lifetimes up to 10$^{30}$ s, offering a better chance of detection across a vast landscape of possible masses.

Elastic and inelastic scattering of cosmic rays on sub-GeV dark matter

We revisit the signatures from collisions of cosmic-rays on sub-GeV dark matter (DM) in the Milky Way. In addition to the upscattered DM component that can be probed by existing DM and neutrino experiments widely discussed, we examine the associated signals in $\gamma$-rays and neutrinos that span a wide energy range due to the inelastic scatterings. Assuming a simple vector portal DM model for illustration, we compute both the upscattered DM flux by cosmic-ray protons, and the resulting emission of secondary $\gamma$-rays and high-energy neutrinos from proton excitation, hadronization, and the subsequent meson decay. We derive limits on coupling constants in the vector portal model using data from the $\gamma$-ray and high-energy neutrino telescopes including Fermi, H.E.S.S. and IceCube. These limits are compared to those obtained by considering the upscattered DM signals at the low-energy DM/neutrino detectors XENON1T/MiniBooNE and the IceCube. For this particular model, the limits are set predominantly by non-detection of the upscattered DM events in XENON1T, for most of the DM mass range due to the large scattering cross section at low energies. Nevertheless, our study demonstrates that the $\gamma$-ray and neutrino signals, traditionally considered as indirect probes for DM annihilation and decay, can also be directly used to constrain the DM--nucleon interaction in complementary to the direct search experiments.

Hunting the Glashow resonance with PeV neutrino telescopes

The Glashow resonant scattering, i.e. ν̄e + e− → W− → anything, offers us a possibility of disentangling ν̄e from the total astrophysical neutrino fluxes. Meanwhile, a great number of high-energy neutrino telescopes, with various detection mechanisms, are advancing towards a better understanding of one of the most energetic frontiers of the Universe. In this work, we investigate a connection between through-going muons at IceCube and the Glashow resonance signal through the channel W− → μ. We find that for IceCube, muons from ν̄e can induce a ∼20% excess of PeV events around the horizontal direction. However, the current statistic of IceCube is not enough to observe such an excess. We also address the novel possibility of ν̄e detection via W− → τ at telescopes aiming to detect Earth-skimming and mountain-penetrating neutrinos. The subsequent hadronic decay of a tau will induce an extensive air shower which can be detected by telescopes with Cherenkov or fluorescence techniques. Similar to IceCube, it is challenging to observe the Glashow resonance excess from the Earth-skimming neutrinos. Nevertheless, we find it is promising to observe Glashow resonance events with a mountain as the target.

CORSIKA Based Simulations of Background in Baikal Experiment

The Baikal experiment aims to register cosmological neutrinos and map the high-energy neutrino sky in the Southern Hemisphere including the region of the Galactic Center. It will use a km3-scale high-energy neutrino telescope located in the southern basin of the Lake Baikal. The northern location of the detector site allows direct observation of the Galactic Center in more than 75 % of the astronomical time. The selection of events from neutrino induced upward going muons, suggests a fairly reliable estimation of the expected background from atmospheric muons. The procedure for simulating background events from atmospheric muons in an array is performed in several steps. The CORSIKA 7.64 was used to simulate the flux of atmospheric muons at the sea level with appropriate chemical composition of the primary cosmic rays. The muon propagation through water and rock to the array level was then simulated with the MUM code. As the last step of the simulation chain, the detector response to the Cherenkov radiation of muons was estimated by taking into account the features of the array measuring systems was performed. The main features of the CORSIKA Monte Carlo code and the next steps of the simulation chain are summarized. The physical models embedded in CORSIKA are described. Application of the full simulation chain is demonstrated.

A Search for Cosmic Neutrino and Gamma-Ray Emitting Transients in 7.3 yr of ANTARES and Fermi LAT Data

Abstract We analyze 7.3 yr of ANTARES high-energy neutrino and Fermi Large Area Telescope (LAT) γ-ray data in search of cosmic neutrino + γ-ray (ν+γ) transient sources or source populations. Our analysis has the potential to detect either individual ν+γ transient sources (durations s), if they exhibit sufficient γ-ray or neutrino multiplicity, or a statistical excess of ν+γ transients of individually lower multiplicities. Individual high γ-ray multiplicity events could be produced, for example, by a single ANTARES neutrino in coincidence with a LAT-detected γ-ray burst. Treating ANTARES track and cascade event types separately, we establish detection thresholds by Monte Carlo scrambling of the neutrino data, and determine our analysis sensitivity by signal injection against these scrambled data sets. We find our analysis is sensitive to ν+γ transient populations responsible for >5% of the observed gamma-coincident neutrinos in the track data at 90% confidence. Applying our analysis to the unscrambled data reveals no individual ν+γ events of high significance; two ANTARES track + Fermi γ-ray events are identified that exceed a once per decade false alarm rate threshold (p = 17%). No evidence for subthreshold ν+γ source populations is found among the track (p = 39%) or cascade (p = 60%) events. Exploring a possible correlation of high-energy neutrino directions with Fermi γ-ray sky brightness identified in previous work yields no added support for this correlation. While TXS 0506+056, a blazar and variable (nontransient) Fermi γ-ray source, has recently been identified as the first source of high-energy neutrinos, the challenges in reconciling observations of the Fermi γ-ray sky, the IceCube high-energy cosmic neutrinos, and ultrahigh-energy cosmic rays using only blazars suggest a significant contribution by other source populations. Searches for transient sources of high-energy neutrinos thus remain interesting, with the potential for either neutrino clustering or multimessenger coincidence searches to lead to discovery of the first ν+γ transients.

Towards an anagraphical picture of high-energy Galactic neutrinos

The TeV/PeV neutrino emission from our Galaxy is related to the distribution of cosmic-ray accelerators, their maximal energy of injection as well as the propagation of injected particles and their interaction with molecular gas. In the last years Interesting upper limits on the diffuse hadronic emission from the whole Galaxy, massive molecular clouds and Fermi Bubbles were set by the IceCube and ANTARES as well as HAWC and Fermi-LAT observations. On the other hand no evidence of Galactic point-like excess has been observed up to now by high-energy neutrino telescopes. This result can be related to the short duration of the PeV hadronic activity of the sources responsible for the acceleration of primary protons, possibly including supernova remnants. All these aspects will be discussed in this work.

Neutrinoless double-beta decay with massive scalar emission

Searches for neutrino-less double-beta decay (0ν2β) place an important constraint on models where light fields beyond the Standard Model participate in the neutrino mass mechanism. While 0ν2β experimental collaborations often consider various massless majoron models, including various forms of majoron couplings and multi-majoron final-state processes, none of these searches considered the scenario where the “majoron” ϕ is not massless, mϕ∼ MeV, of the same order as the Q-value of the 0ν2β reaction. We consider this parameter region and estimate 0ν2βϕ constraints for mϕ of order MeV. The constraints are affected not only by kinematical phase space suppression but also by a change in the signal to background ratio charachterizing the search. As a result, 0ν2βϕ constraints for mϕ>0 diminish significantly below the reaction threshold. This has phenomenological implications, which we illustrate focusing on high-energy neutrino telescopes. The spectral shape of high-energy astrophysical neutrinos could exhibit features due to resonant νν→ϕ→νν scattering. Such features fall within the sensitivity range of IceCube-like experiments, if mϕ is of order MeV, making 0ν2βϕ a key complimentary laboratory constraint on the scenario. Our results motivate a dedicated analysis by 0ν2β collaborations, analogous to the dedicated analyses targeting massless majoron models.

Can BL Lacertae emission explain the neutrinos above 0.2 PeV?

Multi-messenger astronomy can help to investigate the sources of the high-energy neutrinos observed by the high-energy neutrino telescope IceCube. We consider the hypothesis that the highest energy neutrinos are produced by BL Lacs, arguing that this is not contradicted severely by any known fact. We check the BL Lac hypothesis by searching for correlations between the through-going muon events of IceCube and the BL Lacs of the second catalog of Fermi-LAT (2FHL). We expect 10.2 $\pm$ 2.4 correlated events but we find that just 1 event has a BL Lac as counterpart. We also assess the probability of observing one multiplet from the same source, finding that the present null result is not yet of critical significance. We conclude that the hypothesis that the BL Lacs are the main emitters of the highest-energy neutrinos observed by IceCube is disfavored at 3.7{\sigma}. We discuss implications and possible ways out; for example, this could work if the angular resolution was 4{\deg}, which is much more than expected.

Search for high energy neutrinos from bright GRBs with ANTARES

Gamma-ray bursts are a possible site of hadronic acceleration, thus neutrinos are expected in correspondence of a GRB event. The brightest GRB observed between 2008 and 2013 (GRB080916C, GRB110918A, GRB130427A and GRB130505A) have been investigated using the data of the ANTARES high energy neutrino telescope. In this paper two of most promising models of the GRB neutrino emission will be studied: the internal shock model and the photospheric model. No muons have been measured in space and time correlation with the selected GRBs and upper limits at 90% C.L. on the expected neutrino fluxes have been derived. This measure allows also setting constraints on some parameters used in the modeling of the neutrino flux: the bulk Lorentz factor of the jet Г and the baryon loading f p .

High energy neutrino detection with KM3NeT

The KM3NeT Collaboration has started the construction of a next generation high-energy neutrino telescope in the Mediterranean Sea: the largest and most sensitive neutrino research infrastructure. The full KM3NeT detector will be a several cubic kilometres distributed, networked infrastructure. In Italy, off the coast of Capo Passero, and in France, off the coast of Toulon. Thanks to its location in the Northern hemisphere and to its large instrumented volume, KM3NeT will be the optimal instrument to search for neutrinos from the Southern sky and in particular from the Galactic plane, thus making it complementary to IceCube. In this work the technologically innovative component of the detector, the status of construction and the first results from prototypes of the KM3NeT detector will be described as well as its capability to discover neutrino sources are reported.

Probing BSM neutrino physics with flavor and spectral distortions: Prospects for future high-energy neutrino telescopes

The flavor of cosmic neutrinos may help unveil their sources and could reveal the presence of new physics in the neutrino sector. We consider the impacts of next-generation neutrino detectors, including the planned upgrade to neutrino detector--IceCube-Gen2, which is well-positioned to make dramatic improvements in both flavor and spectral measurements. We show that various models in neutrino physics beyond the Standard Model, such as neutrino decay, pseudo-Dirac states, and neutrino self-scattering, may be found or strongly constrained at IceCube-Gen2 and KM3NeT. We find that the additional flavor discriminants given by Glashow resonance events and so-called "double-bang" topologies improve the ability to access the flavor of the cosmic high-energy neutrinos and probe the BSM physics. In addition, although the details depend on source properties, Glashow resonance events have the additional feature of being able to inform us of the relative strengths of neutrino and antineutrino emission, which may help us discriminate astrophysical scenarios.