Physics of Extremely High Energy Cosmic Rays

Over the last third of the century, a few tens of events, detected by ground-based cosmic ray detectors, have opened a new window in the field of high-energy astrophysics. These events have macroscopic energies, unobserved sources, an unknown chemical composition and a production and transport mechanism yet to be explained. With a flux as low as one particle per century per square kilometer, only dedicated detectors with huge apertures can bring in the high-quality and statistically significant data needed to answer those questions. In this article, we review the present status of the field both from an experimental and theoretical point of view. Special attention is given to the next generation of detectors devoted to the thorough exploration of the highest energy rangesComment: 43 pages, 12 figures, submitted to International Journal of Modern Physics

Interpretation of neutrino flux limits from neutrino telescopes on the Hillas plot

We discuss the interplay between spectral shape and detector response beyond a simple E^-2 neutrino flux at neutrino telescopes, at the example of time-integrated point source searches using IceCube-40 data. We use a self-consistent model for the neutrino production, in which protons interact with synchrotron photons from co-accelerated electrons, and we fully take into account the relevant pion and kaon production modes, the flavor composition at the source, flavor mixing, and magnetic field effects on the secondaries (pions, muon, and kaons). Since some of the model parameters can be related to the Hillas parameters R (size of the acceleration region) and B (magnetic field), we relate the detector response to the Hillas plane. In order to compare the response to different spectral shapes, we use the energy flux density as a measure for the pion production efficiency times luminosity of the source. We demonstrate that IceCube has a very good reach in this quantity for AGN nuclei and jets for all source declinations, while the spectra of sources with strong magnetic fields are found outside the optimal reach. We also demonstrate where neutrinos from kaon decays and muon tracks from tau decays can be relevant for the detector response. Finally, we point out the complementarity between IceCube and other experiments sensitive to high-energy neutrinos, at the example of 2004-2008 Earth-skimming neutrino data from Auger. We illustrate that Auger, in principle, is better sensitive to the parameter region in the Hillas plane from which the highest-energetic cosmic rays may be expected in this model.Comment: 28 pages, 10 figures. Substantial clarifications, such as on definition of "sensitivity" and model descriptio

TeV gamma-UHECR anisotropy by decaying nuclei in flight: first neutrino traces?

Ultra High Cosmic Rays) made by He-like lightest nuclei might solve the AUGER extragalactic clustering along Cen A. Moreover He like UHECR nuclei cannot arrive from Virgo because the light nuclei fragility and opacity above a few Mpc, explaining the Virgo UHECR absence. UHECR signals are spreading along Cen-A as observed because horizontal galactic arms magnetic fields, bending them on vertical angles. Cen A events by He-like nuclei are deflected as much as the observed clustered ones; proton will be more collimated while heavy (iron) nuclei are too much dispersed. Such a light nuclei UHECR component coexist with the other Auger heavy nuclei and with the Hires nucleon composition. Remaining UHECR spread group may hint for correlations with other gamma (MeV-Al^{26} radioactive) maps, mainly due to galactic SNR sources as Vela pulsar, the brightest, nearest GeV source. Other nearest galactic gamma sources show links with UHECR via TeV correlated maps. We suggest that UHECR are also heavy radioactive galactic nuclei as Ni^{56}, Ni^{57} and Co^{60} widely bent by galactic fields. UHECR radioactivity (in $\beta$ and $\gamma$ channels) and decay in flight at hundreds keV is boosted (by huge Lorentz factor (nearly a billion) leading to PeVs electrons and consequent synchrotron TeVs gamma offering UHECR-TeV correlated sky anisotropy. Moreover also rarest and non-atmospheric electron and tau neutrinos secondaries at PeVs, as the first two rarest shower just discovered in ICECUBE, maybe the first signature of such expected radioactive secondary tail.Comment: 7 pages,3 figures. arXiv admin note: substantial text overlap with arXiv:1201.015

Air-Shower Spectroscopy at horizons

Horizontal and Upward air-showers are suppressed by deep atmosphere opacity and by the Earth shadows. In such noise-free horizontal and upward directions rare Ultra High Cosmic rays and rarer neutrino induced air-showers may shine, mostly mediated by resonant PeVs interactions in air or by higher energy Tau Air-showers originated by neutrino tau skimming the Earth. At high altitude (mountains, planes, balloons) the air density is so rarefied that nearly all common air-showers might be observed at their maximal growth at a tuned altitude and directions. The arrival angle samples different distances and the corresponding most probable primary cosmic ray energy. The larger and larger distances (between observer and C.R. interaction) make wider and wider the shower area and it enlarge the probability to be observed (up to three order of magnitude more than vertical showers); the observation of a maximal electromagnetic shower development may amplify the signal by two-three order of magnitude (respect suppressed shower at sea level); the peculiar altitude-angle range may disentangle at best the primary cosmic ray energy and composition. Even from existing mountain observatory the up-going air-showers may trace, above the horizons, PeV-EeV high energy cosmic rays and, below the horizons, PeV-EeV neutrino astronomy: their early signals may be captured in already existing gamma telescopes as Magic at Canarie, while facing the Earth edges during (useless) cloudy nights.Comment: 9 pages, 9 figures, submitted to Prog. Part. Nucl. Phy

Simulation of up- and down-going neutrino induced showers at the site of the Pierre Auger Observatory

We present a study about the possibility to detect neutrino induced extensive air showers at the Pierre Auger Observatory. The Monte Carlo simulations performed take into account the details of the neutrino propagation inside the Earth, the air as well as the surrounding mountains which are modelled by a digital elevation map. Details on the sensitivity with respect to the incoming direction as well as the aperture and the total observable event rates are calculated on the basis of various assumptions of the incoming neutrino flux.Comment: Based on a talk presented at European Cosmic Ray Symposium, Lisbon, September 200

Signatures of cosmic tau-neutrinos

The importance and signatures of cosmic tau--(anti)neutrinos have been studied for upward-- and downward--going $\mu^-+\mu^+$ and hadronic shower event rates relevant for present and future underground water or ice detectors, utilizing the unique and reliable ultrasmall--$x$ predictions of the dynamical (radiative) parton model. The upward--going $\mu^- +\mu^+$ event rates calculated just from cosmic $\nu_{\mu}+\bar{\nu}_{\mu}$ fluxes are sizeably enhanced by taking into account cosmic $\nu_{\tau}+ \bar{\nu}_{\tau}$ fluxes and their associated $\tau^- +\tau^+$ fluxes as well. The coupled transport equations for the upward--going $\stackrel{(-)}{\nu}_{\tau}$ flux traversing the Earth imply an enhancement of the attenuated and regenerated $\stackrel{(-)}{\nu}_{\tau}$ flux typically around $10^4-10^5$ GeV with respect to the initial cosmic flux. This enhancement turns out to be smaller than obtained so far, in particular for flatter initial cosmic fluxes behaving like $E_{\nu}^{-1}$. Downward--going $\mu^- +\mu^+$ events and in particular the background--free and unique hadronic `double bang' and `lollipop' events allow to test downward--going cosmic $\nu_{\tau} +\bar{\nu}_{\tau}$ fluxes up to about $10^9$ GeV.Comment: 32 pages, 6 figures; Added reference

Search for a simultaneous signal from small transient events in the Pierre Auger Observatory and the Tupi muon telescopes

We present results of a search for a possible signal from small scale solar transient events (such as flares and interplanetary shocks) as well as possible counterparts to Gamma-Ray Burst (GRB) observed simultaneously by the Tupi muon telescope Niteroi-Brazil, 22.90S, 43.20W, 3 m above sea level) and the Pierre Auger Observatory surface detectors (Malargue-Argentina, 69.30S, 35.30W, altitude 1400 m). Both cosmic ray experiments are located inside the South Atlantic Anomaly (SAA) region. Our analysis of several examples shows similarities in the behavior of the counting rate of low energy (above 100 MeV) particles in association with the solar activity (solar flares and interplanetary shocks). We also report an observation by the Tupi experiment of the enhancement of muons at ground level with a significance higher than 8 sigma in the 1-sec binning counting rate (raw data) in close time coincidence (T-184 sec) with the Swift-BAT GRB110928B (trigger=504307). The GRB 110928B coordinates are in the field of view of the vertical Tupi telescope, and the burst was close to the MAXI source J1836-194. The 5-min muon counting rate in the vertical Tupi telescope as well as publicly available data from Auger (15 minutes averages of the scaler rates) show small peaks above the background fluctuations at the time following the Swift-BAT GRB 110928B trigger. In accordance with the long duration trigger, this signal can possibly suggest a long GRB, with a precursor narrow peak at T-184 sec.Comment: 9 pages, 13 figure

Cherenkov Flashes and Fluorescence Flares on Telescopes: New lights on UHECR Spectroscopy while unveiling Neutrinos Astronomy

Cherenkov Telescopes (as Magic, Hess and Veritas), while pointing horizontally should reveal also the fluorescence flare tails of nearby down-going air-showers. Such air-showers, born at higher (tens km) altitudes, are growing and extending up to lowest atmospheres (EeVs) or up to higher (few km) quotas (PeVs). Viceversa, as it has been foreseen and only recently observed, the opposite takes place. Fluorescence Telescopes made for UHECR detection may be blazed by inclined Cherenkov lights. The geomagnetic splitting may tag the energy as well as the inclined shower footprint as seen in a recent peculiar event in AUGER. Additional stereoscopic detection may define the event origination distance and its consequent primary composition, extending our understanding on UHECR composition, while unveling a novel tau Neutrino Astronomy.Comment: 5 pages, 5 figures, Preprint submitted to Nuclear Instruments and Methods A. Only editorial format chang