Blazars are potential candidates of cosmic-ray acceleration up to ultrahigh energies ($E\gtrsim10^{18}$ eV). For an efficient cosmic-ray injection from blazars, $pγ$ collisions with the extragalactic background light (EBL) and cosmic microwave background (CMB) can produce neutrino spectrum peaks near PeV and EeV energies, respectively. We analyze the contribution of these neutrinos to the diffuse background measured by the IceCube neutrino observatory. The fraction of neutrino luminosity originating from individual redshift ranges is calculated using the distribution of BL Lacs and FSRQs provided in the \textit{Fermi}-LAT 4LAC catalog. Furthermore, we use a luminosity dependent density evolution to find the neutrino flux from unresolved blazars. The results obtained in our model indicate that as much as $\approx10\%$ of the flux upper bound at a few PeV energies can arise from cosmic-ray interactions on EBL. The same interactions will also produce secondary electrons and photons, initiating electromagnetic cascades. The resultant photon spectrum is limited by the isotropic diffuse $γ$-ray flux measured between 100 MeV and 820 GeV. The latter, together with the observed cosmic-ray flux at $E>10^{16.5}$ eV, can constrain the baryonic loading factor depending on the maximum cosmic-ray acceleration energy.
We report the first observational search for tau neutrinos from gamma ray bursts (GRBs) using one of the Ashra light collectors. The earth-skimming tau-neutrino technique of imaging Cherenkov tau showers was applied as a detection method. We set stringent upper limits on the tau-neutrino fluence in PeV-EeV region for 3780 s (between 2.83 and 1.78 hours before) and another 3780 s (between 21.2 and 22.2 hours after) surrounding GRB081203A triggered by the Swift satellite. This first search for PeV-EeV tau neutrino complements other experiments in energy range and methodology, and suggests the pr…
Ultrahigh-energy cosmic rays (UHECRs), if accelerated in the gamma-ray burst (GRB) blastwave, are expected to produce PeV-EeV neutrinos by interacting with long-lived GRB afterglow photons. Detailed spectral and temporal properties of the flux of these neutrinos depend on the GRB blastwave evolution scenario, but can last for days to years time scale in contrast to the seconds to minutes time scale for "burst" neutrino flux contemporaneous with the prompt gamma-ray emission and which has been constrained by IceCube in the $\sim$ 50 TeV-2 PeV range. We compute expected neutrino events in IceCub…
We argue that the excess of sub-PeV/PeV neutrinos recently reported by IceCube could plausibly originate through pion-production processes in the same sources responsible for cosmic rays (CRs) with energy above the second knee around $10^{18}\,$eV. The pion production efficiency for escaping CRs that produce PeV neutrinos is required to be $\gtrsim 0.1$ in such sources. On the basis of current data, we identify semi-relativistic hypernova remants as possible sources that satisfy the requirements. By virtue of their fast ejecta, such objects can accelerate protons to EeV energies, which in turn…
Fast-spinning newborn pulsars are intriguing candidate sources of ultrahigh energy cosmic rays (UHECRs). The acceleration of particles with a given composition in a fraction of the extragalactic pulsar population can give a consistent explanation for the measurements of the Auger Observatory. We calculate the associated diffuse neutrino flux produced while particles cross the supernova ejecta surrounding the stars. We show that in the minimal pulsar scenario that are compatible with the UHECR data, the effective optical depth to hadronuclear interactions is larger than unity at ultrahigh energ…
Cosmic rays around the knee are generally believed to be of galactic origin. Observations on their energy spectrum and chemical composition are important for understanding the acceleration and propagation of these cosmic rays. In addition, it is required to clarify the transition from galactic to extragalactic sources. In this paper, results of recent experiments measuring around the knee will be reviewed along with the detection techniques. The results on the all-particle energy spectrum and composition in the energy range of the knee up to the ankle will be discussed.
The IceCube Neutrino Observatory at the South Pole is a multi-component detector capable of measuring the cosmic ray energy spectrum and composition from PeV to EeV, the energy region typically thought to cover the transition from galactic to extragalactic sources of cosmic rays. The IceTop array at the surface is sensitive to the electromagnetic part of the air shower while the deep in-ice array detects the high-energy (TeV) muonic component of air showers. IceTop's reconstructed shower size parameter, S$_{125}$, is unfolded into a high statistics all-particle energy spectrum. Furthermore, fo…
Archival EAS-MSU data are searched for anomalous muonless events which may be caused by primary gamma rays with energies between 10^15 eV and 10^18 eV. We consider a refined sample of high-quality data and confirm the previously reported detection of a non-zero gamma-ray flux at ~5x10^16 eV with a similar flux value but at somewhat lower statistical significance, corresponding to the depletion of the sample. We present upper limits on the flux below and above these energies, including the first constraints in the range (10^17-10^18) eV never studied by any other experiment.
We report on measurements of the all-particle cosmic ray energy spectrum and composition in the PeV to EeV energy range using three years of data from the IceCube Neutrino Observatory. The IceTop detector measures cosmic ray induced air showers on the surface of the ice, from which the energy spectrum of cosmic rays is determined by making additional assumptions about the mass composition. A separate measurement is performed when IceTop data are analyzed in coincidence with the high-energy muon energy loss information from the deep in-ice IceCube detector. In this measurement, both the spectru…
We show that the PeV neutrinos detected by IceCube put unique constraints on "secret" interactions of neutrinos with the cosmic neutrino background (C$ν$B). The coupling must be $g <0.03$ for the mediating boson mass $m_{X} \lesssim 2$ MeV, $g/m_{X} < 5$ GeV$^{-1}$ for $m_{X} \gtrsim 20$ MeV, and $g/m_{X} < 0.07$ GeV$^{-1}$ in between. We also investigate the possibility that neutrino cascades degrade high-energy neutrinos to PeV energies by upgrading C$ν$B where the energy flux of PeV neutrinos can coincide with the Waxman-Bahcall bound or the cosmogenic neutrino flux for protons, thanks to e…
Star-forming galaxies, due to their high star-formation rates and hence large number of supernova remnants therein, are huge reservoirs of cosmic rays (CRs). These CRs collide with gases in the galaxies and produce high-energy neutrinos through $pp$ collisions. In this paper, we calculate the neutrino production efficiency in star-forming galaxies by considering realistic galaxy properties, such as the gas density and galactic wind in star-forming galaxies. To calculate the accumulated neutrino flux, we use the infrared luminosity function of star-forming galaxies obtained by {\em Herschel} PE…
Data of Pierre Auger Observatory show a proton-dominated chemical composition of ultrahigh-energy cosmic rays spectrum at (1 - 3) EeV and a steadily heavier composition with energy increasing. In order to explain this feature we assume that (1 - 3) EeV protons are extragalactic and derive their maximum acceleration energy, E_p^{max} \simeq 4 EeV, compatible with both the spectrum and the composition. We also assume the rigidity-dependent acceleration mechanism of heavier nuclei, E_A^{max} = Z x E_p^{max}. The proposed model has rather disappointing consequences: i) no pion photo-production on …
We study the effects that the diffusion of the cosmic rays in the magnetic field of the Local Supercluster can have on the spectrum of a nearby extragalactic source at ultrahigh energies. We find that the strong enhancement of the flux below the energy at which the transition between the diffusive and quasirectilinear regimes takes place, as well as the suppression at lower energies associated with a finite source age, can help to explain the observed features of the cosmic-ray spectrum and the composition. Scenarios are discussed in which a nearby extragalactic source with mixed composition a…
A hard $γ$-ray spectrum of supernova remnant G106.3+2.7 can be explained by using the hadronic model with the gluon condensation effect. This implies that not only PeVatrons but also EeVatrons generally exist in the universe including our galaxy, and they can accelerate protons to beyond "ankle" ($10^{19}~eV$). Although these proton beams are very weak in the galaxy and cannot be observed individually on the earth, the gluon condensation effect may greatly enhance the proton-proton cross section, which can compensate for the weak proton flux and produce the observed $γ$-rays. We also show that…
Cosmic-Ray Physics in the PeV to EeV Energy Range with the IceCube-Gen2 Surface Array (ICRC 2025)
Bartol Research Institute, Department of Physics and Astronomy, University of Delaware（特拉华大学巴托尔物理与天文学研究所）；Institute for Astroparticle Physics, Karlsruhe Institute of Technology (KIT)（卡尔斯鲁厄理工学院高能粒子物理研究所）
We report on a measurement of the cosmic ray composition by the Telescope Array Low-Energy Extension (TALE) air fluorescence detector (FD). By making use of the Cherenkov light signal in addition to air fluorescence light from cosmic ray (CR) induced extensive air showers, the TALE FD can measure the properties of the cosmic rays with energies as low as $\sim 2$ PeV and exceeding 1 EeV. In this paper, we present results on the measurement of $X_{\rm max}$ distributions of showers observed over this energy range. Data collected over a period of $\sim 4$ years was analyzed for this study. The re…
Observations of TeV--PeV-energy cosmic neutrinos by the IceCube observatory have suggested that extragalactic cosmic-ray sources should have an optical depth greater than $\sim$0.01 and contribute to more than 10\% of the observed bulk of cosmic rays at 10 PeV. If the spectrum of cosmic rays from these extragalactic sources extends well beyond 1 EeV, the neutrino flux indicates that extragalactic cosmic-ray protons are dominant in the observed total cosmic-ray flux at 1 EeV. Among known powerful astronomical objects, including gamma-ray bursters (GRBs), only flat-spectrum radio quasars could (…
From GeV to PeV: Orbital Modulation and Wind-Regulated Ultrahigh-energy Emission in Cygnus~X-3
School of Astronomy and Space Science, Nanjing University（南京大学天文与空间科学学院）；Key Laboratory of Modern Astronomy and Astrophysics (Nanjing University), Ministry of Education（教育部现代天文学和天体物理学重点实验室（南京大学））；Tianfu Cosmic Ray Research Center（天府宇宙线研究中心）；State Key Laboratory of Particle Astrophysics, Institute of High Energy Physics, Chinese Academy of Sciences（中国科学院高能物理研究所粒子天体物理国家重点实验室）
The observation of ultra-high-energy EeV-energy cosmogenic neutrinos provides a direct path to identifying the sources of the highest energy cosmic rays; searches have so far resulted in only upper limits on their flux. However, with the realization of cubic-kilometer detectors such as IceCube and, in the near future, KM3NeT, GVD-Baikal, and similar instruments, we anticipate the observation of PeV-energy cosmic neutrinos with high statistics. In this context, we draw attention to the opportunity to identify EeV tau neutrinos at PeV energy using Earth-traversing tau neutrinos. We show that Che…
Flat Spectrum Radio Quasars (FSRQ) are the most powerful blazars in the gamma-ray band. Although they are supposed to be good candidates in producing high energy neutrinos, no secure detection of FSRQs has been obtained up to now, except for a possible case of PKS B1424-418. In this work, we compute the expected flux of high energy neutrinos from FSRQs using standard assumptions for the properties of the radiation fields filling the regions surrounding the central supermassive black hole. We obtain as a result that high energy neutrinos are naturally expected from FSRQs in the sub-EeV-EeV ener…
Long duration gamma-ray bursts are powerful sources that can accelerate particles to ultra-high energies. Acceleration of protons in the forward shock of the highly relativistic GRB blastwave allows PeV--EeV neutrino production by photopion interactions of ultra-high energy protons with X-ray to optical photons of the GRB afterglow emission. Four different blastwave evolution scenarios are considered: adiabatic and fully radiative blastwaves in a constant density circumburst medium and in a wind environment with the particle density in the wind decreasing inversley proportional to the square o…
We describe a method of observation for PeV--EeV tau neutrinos using Cherenkov light from the air showers of decayed taus produced by tau neutrino interactions in the Earth. Aiming for the realization of neutrino astronomy utilizing the Earth-skimming tau neutrino detection technique, highly precise determination of arrival direction is key due to the following issues: (1) Clear identification of neutrinos by identifying those vertices originating within the Earth's surface; (2) Identification of very high energy neutrino sources. The Ashra detector uses newly developed light collectors which …
The SPHERE-2 balloon-borne detector designed for extensive air shower (EAS) observations using EAS optical Vavilov-Cherenkov radiation (``Cherenkov light''), reflected from the snow-covered surface of Lake Baikal is described. We briefly discuss the concept behind the reflected Cherenkov light method, characterize the conditions at the experimental site and overview the construction of the tethered balloon used to lift the SPHERE-2 telescope above the surface. This paper is mainly dedicated to a detailed technical description of the detector, including its optical system, sensitive elements, e…
The PeV gamma ray background produced in the interactions of ultra high energy cosmic rays with the ambient matter and radiations during their propagation in the Milky Way has been calculated in this paper. If the primary ultra high energy cosmic rays are produced from Galactic point sources then those point sources are also emitting PeV gamma rays. We discuss that the detection of galactocentric PeV gamma rays in the future would be a signature of the presence of EeV cosmic accelerators in the Milky Way.
Impact of the EPOS.LHC-R hadronic interaction model on the Centaurus A ultrahigh-energy cosmic-ray scenario
Centro Atómico Bariloche, Comisión Nacional de Energía Atómica（巴里洛切原子能中心，国家原子能委员会）；Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET)（国家科学研究委员会）
Cosmic neutrino events detected by the IceCube Neutrino Observatory with energy $\gtrsim 30$ TeV have poor angular resolutions to reveal their origin. Ultrahigh-energy cosmic rays (UHECRs), with better angular resolutions at $>60$ EeV energies, can be used to check if the same astrophysical sources are responsible for producing both neutrinos and UHECRs. We test this hypothesis, with statistical methods which emphasize invariant quantities, by using data from the Pierre Auger Observatory, Telescope Array and past cosmic-ray experiments. We find that the arrival directions of the cosmic neutrin…
We study general implications of the IceCube observations in the energy range from $10^{6}$ GeV to $10^{10}$ GeV for the origin of extragalactic ultrahigh energy cosmic rays assuming that high energy neutrinos are generated by the photomeson production of protons in the extragalactic universe. The PeV-energy neutrino flux observed by IceCube gives strong bounds on the photomeson-production optical depth of protons in their sources and the intensity of the proton component of extragalactic cosmic rays. The neutrino flux implies that extragalactic cosmic-ray sources should have the optical depth…
The IceCube experiment recently detected the first flux of high-energy neutrinos in excess of atmospheric backgrounds. We examine whether these neutrinos originate from within the same extragalactic sources as ultrahigh-energy cosmic rays. Starting from rather general assumptions about spectra and flavors, we find that producing a neutrino flux at the requisite level through pion photoproduction leads to a flux of protons well below the cosmic-ray data at ~10^18 eV, where the composition is light, unless pions/muons cool before decaying. This suggests a dominant class of accelerator that allow…
The observation of neutrinos from cosmic accelerators will be revolutionary. High energy neutrinos are closely connected to ultrahigh energy cosmic rays and their sources. Cosmic ray sources are likely to produce neutrinos and the propagation of ultrahigh cosmic rays from distant sources can generate PeV to ZeV neutrinos. We briefly review recent progress on the observations of ultrahigh energy cosmic rays and their implications for the future detections of high energy neutrinos.
In this work, we present detailed simulations for propagation of ultra-high energy (UHE) heavy nuclei, with E > 60 EeV, within recent Galactic Magnetic Field (GMF) models. We investigate the impacts of the regular and turbulent components of the GMF. We show that with UHE heavy nuclei, there is no one-to-one correspondence between the arrival directions of cosmic rays (CR) measured at Earth and the direction of their extragalactic sources. Sources can have several distorted images on the sky. We compute images of galaxy clusters and of the supergalactic plane in recent GMF models and show the …
I study the possibility of probing Ultra-High Energy (UHE from now on) dark matter particles (>10$^8$ GeV) due to the decay of superheavy dark matter via detection of UHE neutrino signatures from the earth core. The UHE WIMP event rates are estimated at the energies of 100 PeV, and 1 EeV, 10 EeV, 100 EeV and 1 ZeV in JEM-EUSO and at the energy of 1 ZeV in IceCube, respectively. The diffuse neutrino contaminations are also roughly estimated in JEM-EUSO and IceCube. I found that the extreme energy WIMPs can be detected by JEM-EUSO above 1 EeV and by IceCube above 1 ZeV in the $χ$ mass range of 1…
Searches for large-scale anisotropies in the distribution of arrival directions of cosmic rays detected above $\simeq 10 $PeV at the Pierre Auger Observatory are presented. Although no significant deviation from isotropy is revealed at present, some of the measurements suggest that future data will provide hints for large-scale anisotropies over a wide energy range. Those anisotropies would have amplitudes which are too small to be significantly observed within the current statistics. Assuming that the cosmic ray anisotropy is dominated by dipole and quadrupole moments in the EeV-energy range,…
Two EAS arrays during a day have recorded 3 particles with energies above 30 EeV arriving from the same sky region. Two events were registered by the Yakutsk array and one - by the Telescope Array. Two Yakutsk events were estimated to be same energy and the Telescope Array shower's energy was almost 2 times higher. This indicates the same magnetic rigidity of all three particles, if the charge differs by a factor of 2. The relatively short sequence of all three events and their "monochromaticity" in rigidity can be due to the magnetic separation of particles in the acceleration process and pro…
While propagating from their source to the observer, ultrahigh energy cosmic rays interact with cosmological photon backgrounds and generate to the so-called "cosmogenic neutrinos". Here we study the parameter space of the cosmogenic neutrino flux given recent cosmic ray data and updates on plausible source evolution models. The shape and normalization of the cosmogenic neutrino flux are very sensitive to some of the current unknowns of ultrahigh energy cosmic ray sources and composition. We investigate various chemical compositions and maximum proton acceleration energies E_p,max which are al…
Yukawa Institute for Theoretical Physics, Kyoto University（京都大学汤川理论物理研究所）；The Pennsylvania State University（宾夕法尼亚州立大学）；Virginia Tech（弗吉尼亚理工大学）；The University of Tokyo（东京大学）
The origins of the diffuse flux of cosmogenic PeV neutrinos detected in the IceCube experiment during 2010 - 2017 remain unidentified. A population of extragalactic newly born fast spinning pulsars are investigated as possible candidates for generating the PeV energy scale neutrinos. A two-step mechanism of particle acceleration is adopted for transferring energy from star rotation to high energy electrons. Electrons might be boosted up to $\approx 0.01$ EeV energies and above, and produce ultra-high-energy (UHE) neutrinos and gamma rays when these electrons interact with low energy positrons …
Recent ultrahigh energy gamma-ray observations by the HAWC up to 100 TeV and LHAASO observatories up to 1.4 PeV energies from the direction of Fermi-LAT 4FGL source 4FGL J2028.6+4110e (Cygnus Cocoon), are indicative of a hadronic origin over a leptonic process for their creation. The IceCube Neutrino Observatory has reported IceCube-201120A, a neutrino event coming from the same direction, suggesting that the Cygnus Cocoon may correspond to one of the most plausible sources of high-energy cosmic rays. The apparent relationship of the neutrino event with the observed ultra high energy gamma-ray…
Ultrahigh energy cosmic rays are the most energetic of any subatomic particles ever observed in nature. The quest for their mysterious origin is currently a major scientific challenge. Here we explore the possibility that these particles originate from nearby starburst galaxies, a scenario that matches the recent observation by the Telescope Array experiment of a cosmic-ray hotspot above 57~EeV not far from the direction of the starburst galaxy M82. Specifically, we study the stochastic propagation in space of ultrahigh energy cosmic rays through the state-of-the-art simulation framework CRPro…
A Unified Framework for 10 TeV to EeV Diffuse Neutrino Sky and KM3-230213A
Department of Physics and Astronomy, University of Utah（犹他大学物理与天文学系）；Key Laboratory of Particle Astrophysics and Experimental Physics Division and Computing Center, IHEP, CAS（中国科学院高能物理研究所粒子天体物理重点实验室及实验物理部计算中心）；TIANFU Cosmic Ray Research Center, Chengdu, Sichuan, China（中国四川成都天府宇宙线研究中心）
We report on a measurement of the cosmic ray energy spectrum by the Telescope Array Low-Energy Extension (TALE) air fluorescence detector. The TALE air fluorescence detector is also sensitive to the Cherenkov light produced by shower particles. Low energy cosmic rays, in the PeV energy range, are detectable by TALE as "Cherenkov Events". Using these events, we measure the energy spectrum from a low energy of $\sim 2$ PeV to an energy greater than 100 PeV. Above 100 PeV TALE can detect cosmic rays using air fluorescence. This allows for the extension of the measurement to energies greater than …
The origin of recently discovered PeV neutrinos is an unsolved problem. In this work we consider a hadronic scenario to produce PeV neutrinos from a region around giant lobes of Centaurus A. Although ultrahigh-energy cosmic rays (UHECRs) are accelerated and confined by giant lobes, they can escape to be later injected in the inter-group medium where galaxies near the giant lobes provides the condition to confine them. UHECRs interact with low-energy photons and protons producing high-energy photons and neutrinos. We found that the IC35 event cannot be generated neither inside the giant lobes n…
We study the propagation of ultra-high-energy cosmic rays (UHECR) in the Galaxy, concentrating on the energy range below the ankle in the spectrum at 4 EeV. A Monte-Carlo method, based on analytical solutions to the time-dependent diffusion problem, is used to account for intermittency by placing sources at random locations. Assuming a source population that scales with baryon mass density or star formation (e.g. long GRB), we derive constraints arising from intermittency and the observational limits on the composition and anisotropy. It is shown that the composition and anisotropy at 1e18 eV …
We report on the measurement of the all-particle cosmic ray energy spectrum with the IceTop air shower array in the energy range from 1.58 PeV to 1.26 EeV. The IceTop air shower array is the surface component of the IceCube Neutrino Observatory at the geographical South Pole. The analysis was performed using only information from IceTop. The data used in this work were taken from June 1, 2010 to May 13, 2011. During that period the IceTop array consisted of 73 stations compared to 81 in its final configuration. The measured spectrum exhibits a clear deviation from a single power law above the …
We present a range of unbroken power-law fits to the astrophysical-neutrino spectrum consistent with the most recent published IceCube data at the 68\% confidence level. Assuming that the neutrinos originate in decays of pi mesons, we estimate accompanying gamma-ray fluxes for various distributions of sources, taking propagation effects into account. We then briefly discuss existing experimental results constraining PeV to EeV diffuse gamma-ray flux and their systematic uncertainties. Several scenarios are marginally consistent both with the KASKADE and CASA-MIA upper limits at (10^15-10^16) e…
It has been long debated whether the high-energy gamma-ray radiation from the Crab nebula stems from leptonic or hadronic processes. In this work, we investigate the multi-band non-thermal radiation from the Crab pulsar wind nebula with the leptonic and leptonic-hadronic hybrid models, respectively. Then we use the Markov Chain Monte Carlo(MCMC) sampling technology and method of sampling trace to study the stability and reasonability of the model parameters according to the recent observed results and obtain the best-fitting values of parameters. Finally, we calculate different radiative compo…
The images of ultrahigh-energy cosmic ray sources get distorted, in an energy dependent way, by the effects of Galactic and extragalactic magnetic fields. These deflections can also affect the observed cosmic ray spectrum, specially when the sources are transient. We study scenarios in which one or a few nearby extragalactic sources, such as CenA or M81/M82, provide the dominant contribution to the cosmic ray flux above the ankle of the spectrum. We discuss the effects of the angular dispersion induced by the turbulent extragalactic magnetic fields, and the coherent deflections caused by the r…
We present an updated cosmic-ray mass composition analysis in the energy range $10^{16.8}$ to $10^{18.3}$ eV from 334 air showers measured with the LOFAR radio telescope, and selected for minimal bias. In this energy range, the origin of cosmic rays is expected to shift from galactic to extragalactic sources. The analysis is based on an improved method to infer the depth of maximum $X_{\rm max}$ of extensive air showers from radio measurements and air shower simulations. We show results of the average and standard deviation of $X_{\rm max}$ versus primary energy, and analyze the $X_{\rm max}$-…
Important observational results have been recently reported on the angular distributions of cosmic rays at all energies, calling into question the perception of cosmic rays a decade ago. These results together with their in-progress interpretations are summarised in this review paper, covering both large-scale and small-scale anisotropies from TeV energies to the highest ones. While the magnetic field in the Galaxy has long been considered as an external data imprinting a quasi-random walk to particles and thus shaping the angular distributions of Galactic cosmic rays through the induced avera…
Point source searches with neutrino telescopes like IceCube are normally restricted to one hemisphere, due to the selection of up-going events as a way of rejecting the atmospheric muon background. In this work we show that the down-going region above the horizon can be included in the search by suppressing the background through energy-sensitive selection procedures. This approach increases the reach to the EeV regime of the signal spectrum, which was previously not accessible due to the absorption of neutrinos with energies above a PeV inside the Earth. We present preliminary results of this…
The observation of ultrahigh energy (UHE) neutrinos has become a priority in experimental astroparticle physics. UHE neutrinos can be detected with a variety of techniques. In particular, neutrinos can interact in the atmosphere (downward-going neutrinos) or in the Earth crust (Earth-skimming neutrinos), producing air showers that can be observed with arrays of detectors at the ground. With the Surface Detector Array of the Pierre Auger Observatory we can detect these types of cascades. The distinguishing signature for neutrino events is the presence of very inclined showers produced close to …
