Narrow Results

We show that the cascade limit on ultra high energy cosmic neutrino (UHECν) flux imposes a lower bound on the neutrino mass, provided that super-GZK events of ultra high energy cosmic rays (UHECRs) are produced from Z-bursts. Based on data from HiRes and AGASA, the lower bound obtained on neutrino mass violates its existing cosmological upper bound. We conclude that Z-bursts cannot be the dominant source for the observed super-GZK UHECR events. This is consistent with the recent ANITA-lite data.

The Antarctic Muon And Neutrino Detector Array (AMANDA) has been taking data since 2000 and its data acquisition system was upgraded in January 2003 to read out the complete digitized waveforms from the buried Photomultipliers (PMTs) using Transient Waveform Recorders (TWR). This system currently runs in parallel with the standard AMANDA data acquisition system. Once AMANDA is incorporated into the 1 km³ detector IceCube, only the TWR system will be kept. We report results from a first atmospheric neutrino analysis on data collected in 2003 with TWR. Good agreement in event rate and angular distribution verify the performance of the TWR system. A search of the northern hemisphere for localized event clusters shows no statistically significant excess, thus a flux limit is calculated, which is in full agreement with previous results based on the standard AMANDA data acquisition system. We also update the status of a search for diffusely distributed neutrinos with ultra high energy (UHE) using data collected by the TWR system.

The ANtarctic Impulse Transient Antenna (ANITA) is the first long-duration balloon experiment designed to search and measure the flux of Greisen–Zapsepin–Kuzmin (GZK) neutrinos. We present new limits on neutrinos fluxes of astronomical origin from data collected with the successful launch of a 2-antenna prototype instrument, called ANITA-lite, that circled the Antarctic continent for 18.4 days in January 2004. We performed a search for Ultra-High-Energy (UHE) neutrinos with energies above 3 × 10¹⁸eV. No excess events above the background expectation were observed and a neutrino flux following E^-2 spectrum for all neutrino flavors, is limited to for 10^18.5eV < E_ν < 10^23.5eV at 90% confidence level. The launch of ANITA is scheduled for December 2006. Looking beyond ANITA, we describe a new idea, called ARIANNA (Antarctic Ross Iceshelf ANtenna Neutrino Array), to increase the sensitivity for GZK neutrinos by one order of magnitude better than ANITA.

This paper summarizes some recent experimental results in very high energy astrophysics, a very active research area with many exciting developments both in theory and observation.

We present recent results from the Antarctic Muon And Neutrino Detector Array (AMANDA), located at the South Pole in Antarctica. AMANDA-II, commissioned in 2000, is a multipurpose high energy neutrino telescope with a broad physics and astrophysics scope. We summarize the results from searches for a variety of sources of ultra-high energy neutrinos: TeV-PeV diffuse sources by measuring either muon tracks or cascades, neutrinos in excess of PeV by searching for muons traveling in the down-going direction and point sources.

The AMANDA neutrino telescope has been in operation at the South Pole since 1996. The present final array configuration, operational since 2000, consists of 677 photomultiplier tubes arranged in 19 strings, buried at depths between 1500 and 2000 m in the ice. The most recent results on a multi-year search for point sources of neutrinos will be shown. The study of events triggered in coincidence with the surface array SPASE and AMANDA provided a result on cosmic ray composition. Expected improvements from IceCube/IceTop will also be discussed.

New results from the Baikal neutrino telescope NT200, based on the first 5 years of operation (1998–2003), are presented. We derive an all-flavor limit on the diffuse flux of astrophysical neutrinos between 20 TeV and 50 PeV, extract an enlarged sample of high energy muon neutrino events, and obtain limits on the flux of high energy atmospheric muons. In 2005, the upgraded telescope NT200+ will be commissioned: 3 additional distant strings with only 12 photo-multipliers each will rise the effective volume to 20 Mton at 10 PeV for this largest running neutrino telescope in the Northern hemisphere.

ANTARES is a neutrino telescope under construction in the Mediterranean Sea at the depth of 2500 m, about 40 km off the French coast. A short review of its design and expected performances is presented as well as the status of the project.

The physics of Cosmic Rays of Extreme Energy will be deeply investigated by the next generation of fluorescence space detectors. For the Extreme Energy Neutrino Astronomy such detectors will probably exhibit a lack of statistics and a further increase of sensitivity will be necessary for this goal. The critical items in designing a future Neutrino Space Observatory suited for Neutrino Astronomy are discussed.

The KM3NeT research infrastructure includes two underwater Cherenkov telescopes in the Mediterranean Sea, KM3NeT/ARCA and KM3NeT/ORCA. The detectors are under construction but are currently taking data and the first physics results were already obtained. The detection technology is the same for both telescopes but the detector geometries are different as they have been tailored to different scientific goals. The KM3NeT/ARCA telescope, located off-shore the Sicilian coast in Italy, focuses on studying the high-energy cosmic neutrinos in the TeV–PeV energy range. The KM3NeT/ORCA location is off-shore Toulon in France and its main goal is to explore the atmospheric neutrino oscillations in the GeV energy range. An overview of the recent results achieved with the KM3NeT detectors in their partial configurations is given in this work. Also, the sensitivity to the cosmic neutrino measurements and the oscillation studies with the completed KM3NeT/ARCA and KM3NeT/ORCA telescopes are presented.

The Sun albedo of Cosmic Rays (CRs) at GeVs energy has been discovered recently by the FERMI satellite. They are traces of atmospheric CRs hitting solar atmosphere and reflecting skimming gamma photons. Even if relevant for astrophysics, as being a trace of atmospheric solar CR noises they cannot offer any signal of neutrino astronomy. On the contrary, the Moon with no atmosphere, may become soon a novel filtering calorimeter and an amplifier of energetic muon astronomical neutrinos (at TeV up to hundred TeVs energy); these lepton tracks leave an imprint in their beta decay while in flight to Earth. Their TeV electron air-shower are among the main signals. Also, a more energetic, but more rare, PeV up to EeV tau lunar neutrino events may be escaping as a tau lepton from the Moon: $\tau$ PeV secondaries, then, may be shining on Earth’s atmosphere in lunar shadows in a surprising way. One or a few gamma air-shower events inside the Moon shadows may occur each year in near future Cherenkov telescope array (CTA) or large high altitude air shower observatory (LHAASO) TeV gamma array detector, assuming a nonnegligible astrophysical TeV up to hundred TeV neutrino component (with respect to our terrestrial ruling atmospheric ones); these signals will open a new wonderful passe-partout keyhole for neutrino, been seen along the Moon. The lunar solid angle is small and the muon or tau expected rate is rare, but with the future largest tau radio array as the giant radio array for neutrino detection (GRAND), one might well discover such neutrino imprint.

The IceCube neutrino telescope discovered PeV-energy neutrinos originating beyond our Galaxy with an energy flux that is comparable to that of GeV-energy gamma rays and EeV-energy cosmic rays. These neutrinos provide the only unobstructed view of the cosmic accelerators that power the highest energy radiation reaching us from the universe. We will review the results from IceCube’s first decade of operations, emphasizing the measurement of the diffuse multiflavored neutrino flux from the universe and the identification of the supermassive black hole TXS $0506+056$ as a source of cosmic neutrinos and, therefore, cosmic rays. We will speculate on the lessons learned for multimessenger astronomy, among them that extragalactic neutrino sources may be a relatively small subset of the cosmic accelerators observed in high-energy gamma rays and that these may be gamma-ray-obscured at the times that they emit neutrinos.

To search for transient astrophysical neutrino sources, IceCube’s optical and X-ray follow-up program is triggered by two or more neutrino candidates arriving from a similar direction within 100 s. However, the rate of such neutrino multiplets was found to be consistent with the expected background of chance coincidences, such that the data does not provide indications for the existence of short-lived transient neutrino sources. Upper limits on the neutrino flux of transient source populations are presented in Aartsen et al. (2019) and we show here how these limits apply to the predicted neutrino emission from binary neutron star mergers.

The Antarctic Muon And Neutrino Detector Array (AMANDA) has been taking data since 2000 and its data acquisition system was upgraded in January 2003 to read out the complete digitized waveforms from the buried Photo-multipliers (PMTs) using Transient Waveform Recorders (TWR). This system currently runs in parallel with the standard AMANDA data acquisition system. Once AMANDA is incorporated into the 1 km³ detector IceCube, only the TWR system will be kept. We report results from a first atmospheric neutrino analysis on data collected in 2003 with TWR. Good agreement in event rate and angular distribution verify the performance of the TWR system. A search of the northern hemisphere for localized event clusters shows no statistically significant excess, thus a flux limit is calculated, which is in full agreement with previous results based on the standard AMANDA data acquisition system. We also update the status of a search for diffusely distributed neutrinos with ultra high energy (UHE) using data collected by the TWR system.

The ANtarctic Impulse Transient Antenna (ANITA) is the first long-duration balloon experiment designed to search and measure the flux of Greisen-Zapsepin-Kuzmin (GZK) neutrinos. We present new limits on neutrinos fluxes of astronomical origin from data collected with the successful launch of a 2-antenna prototype instrument, called ANITA-lite, that circled the Antarctic continent for 18.4 days in January 2004. We performed a search for Ultra-High-Energy (UHE) neutrinos with energies above 3 × 10¹⁸eV. No excess events above the background expectation were observed and a neutrino flux following E⁻² spectrum for all neutrino flavors, is limited to for 10^18.5eV < E_ν < 10^23.5eV at 90% confidence level. The launch of ANITA is scheduled for December 2006. Looking beyond ANITA, we describe a new idea, called ARIANNA (Antarctic Ross Iceshelf ANtenna Neutrino Array), to increase the sensitivity for GZK neutrinos by one order of magnitude better than ANITA.

The ANTARES collaboration has recently demonstrated a rapid progress in the construction of the 0.1 km²-scale neutrino detector in the Mediterranean sea. At present the underwater setup consists of 5 active detector "lines" (of the 12 lines foreseen in the final configuration) and it is taking physics data with nearly nominal efficiency. Currently the atmospheric muon flux and its angular distribution are under intensive studies. Meanwhile over hundred upward-going neutrino events have been extracted from the largely overwhelming background originated by the downward going muons. Thus the concept and the design of the undersea experiment now appear to be confidently proved. The detector construction is to be completed in spring 2008.

The flavor composition of ultra-high energy cosmic neutrinos (UHECN) carries precious information about the physical properties of their sources, the nature of neutrino oscillations and possible exotic physics involved during the propagation. Since UHECN with different incoming directions would propagate through different amounts of matter in Earth and since different flavors of charged leptons produced in the neutrinonucleon charged-current (CC) interaction would have different energy-loss behaviors in the medium, measurement of the angular distribution of incoming events by a neutrino observatory can in principle be employed to help determine the UHECN flavor ratio. In this paper we report on our investigation of the feasibility of such an attempt. Simulations were performed, where the detector configuration was based on the proposed Askaryan Radio Array (ARA) Observatory at the South Pole, to investigate the expected event-direction distribution for each flavor. Assuming ν_μ-ν_τ symmetry and invoking the standard oscillation and the neutrino decay scenarios, the probability distribution functions (PDF) of the event directions are utilized to extract the flavor ratio of cosmogenic neutrinos on Earth. The simulation results are summarized in terms of the probability of flavor ratio extraction and resolution as functions of the number of observed events and the angular resolution of neutrino directions. We show that it is feasible to constrain the UHECN flavor ratio using the proposed ARA Observatory.

After the discovery of a cosmic neutrino diffuse flux by the IceCube detector, the search for its origin has become a key mission in high energy astrophysics. Particularly interesting is the indication (although not significant with the present IceCube statistics) of an excess of signal events from the Southern sky: this region is where the ANTARES detector, the largest neutrino telescope in the Northern hemisphere, is at its best for what concerns sensitivity and performance. Indeed, the ANTARES sensitivity is good enough to constrain the origin of a fraction of the IceCube excess. Assuming different spectral indexes for the energy spectrum of neutrino emitters, the Southern sky and in particular central regions of our Galaxy are studied, searching for point-like objects and for extended regions of emission; the results of the unblinded analyses will be presented.

An unambiguous identification of the emitting neutrino sources of the high-energy cosmic neutrino flux reported by Icecube requires km3 neutrino telescopes with a large sky coverage and good angular resolution. The KM3NeT Collaboration aims at building a cubic kilometre scale neutrino telescope in the depths of the Mediterranean Sea. The detector technology has been validated with prototypes operating at a depth of 2500m and 3500m. The modular nature of the detector allows for a staged implementation with increasing size. KM3NeT phase-1, made of 32 structures with an instrumented volume of 0.1 km-cube, has been funded and will be deployed off-shore Capo Passero-Italy (KM3NeT-It) by 2016. Following this phase, a project called KM3NeT 2.0 has been proposed with an upgraded physics program including the measure of the neutrino mass hierarchy off-shore Toulon (ORCA). KM3NeT/ARCA, the extension of the phase- 1 detector to 1-2 km³, will be dedicated to high-energy neutrino astronomy, allowing the almost full survey of the neutrino sky including the region of the galactic centre. The characteristics of sea water allow to measure the neutrino direction with very good angular resolution also for cascade events. The KM3NeT/ARCA sensitivity will allow to detect the flux measured by Icecube within less than one year of observation, while within about four years of observation KM3NeT/ARCA could give indications at 3-sigma level on some candidate galactic point-like sources.

ANTARES (Astronomy with a Neutrino Telescope and Abyss environmental RESearch) is currently the largest neutrino detector on the Northern Hemisphere. The detector consists of twelve lines, carrying 885 ten-inch photomultipliers in total, placed at a depth of about 2480 meters in the Mediterranean Sea near Toulon, France. The PMTs detect Cherenkov light emitted by muons from neutrino charged current interactions in the surrounding seawater and the rock below. The neutrinos momentum is transferred to the muons allowing for reconstruction of the neutrinos direction. The goals of ANTARES are among others the search for astrophysical neutrino point sources and for neutrinos produced in self-annihilation of dark matter particles. A likely source of the latter type of neutrino emission would be the Sun, where dark matter particles from the galactic halo are expected to accumulate. ANTARES is taking data with its full twelve line configuration since May 2008, and has been before in a five and ten line setup for more than a year. First results on the search for dark matter annihilation in the Sun, and their interpretation in the framework of mSugra are presented, as well as sensitivity studies on Dark Matter search with the full ANTARES detector and the future large undersea KM3NeT neutrino telescope.