After over 60 years, the powerful engines that accelerate ultra-high-energy cosmic rays (UHECRs) to the formidable energies at which we observe them from Earth remain mysterious. Assuming standard ...physics, we expect UHECR sources to lie within the local Universe (up to a few hundred Mpc). The distribution of matter in the local Universe is anisotropic, and we expect this anisotropy to be imprinted on the distribution of UHECR arrival directions. Even though intervening intergalactic and Galactic magnetic fields deflect charged UHECRs and can distort these anisotropies, some amount of information on the distribution of the sources is preserved. In this proceedings contribution, we present the results of the joint Pierre Auger Observatory and Telescope Array searches for (a) the largest-scale anisotropies (the harmonic dipole and quadrupole) and (b) correlations with a sample of nearby starburst galaxies and the 2MRS catalogue tracing stellar mass within 250 Mpc. This analysis updates our previous results with the most recent available data, notably with the addition of 3 years of new Telescope Array data. The main finding is a correlation between the arrival directions of 12.1%
−3.1%
+4.5%
of UHECRs detected with
E ≥
38 EeV by Auger or with
E ≳
49 EeV by TA and the positions of nearby starburst galaxies on a 15.1°
−3.0°
+4.6°
angular scale, with a 4.7σ post-trial significance, up from 4.2σ obtained in our previous study.
High-energy neutrinos are expected to be produced by the interaction of accelerated particles near the acceleration sites. For this reason, it is intresting to search for correlation in the arrival ...directions of ultra–high energy cosmic rays (UHECRs) and HE neutrinos. We present here the results of a search for correlations between UHECR events measured by the Pierre Auger Observatory and Telescope Array and high-energy neutrino candidate events from IceCube and ANTARES. We perform a cross-correlation analysis, where the angular separation between the arrival directions of UHECRs and neutrinos is scanned. When comparing the results with the expectations from a null hypothesis contemplating an isotropic distribution of neutrinos or of UHECR we obtain post-trial p-values of the order of ~ 10
2
.
The origin of ultra-high-energy cosmic rays (UHECRs) is still unknown. Their sources are believed to be within the local universe (a few hundred megaparsecs), but deflections by intergalactic and ...Galactic magnetic fields prevent us from straightforwardly associating UHECRs to their sources based on their arrival directions, making their angular distribution mostly isotropic. At higher energies, the number of potential source candidates and the magnetic deflections are both expected to be smaller, but so is the available amount of statistics. Hence, it is interesting to perform searches for anisotropies using several different energy thresholds. With a threshold of 8 EeV a dipole modulation has been discovered, and with higher thresholds evidence is mounting for correlations with certain nearby galaxies. Neither of the two main UHECR detectors, the Pierre Auger Observatory and the Telescope Array project, has full-sky coverage. Full-sky searches require combining the datasets of both, and a working group with members of both collaborations has been tasked with this. We present an overview of the challenges encountered in such analyses, recent results from the working group, possible ways of interpreting them, and an outlook for the near future.
We present the results of three searches for correlations between ultra-high energy cosmic ray events (UHECRs) measured by Telescope Array and the Pierre Auger Observatory and high-energy neutrino ...candidate events from IceCube. Two cross-correlation analyses of UHECRs are done: one with 28 "cascades" from the IceCube 'high-energy starting events' sample and the other one with 12 high-energy "tracks". The angular separation between the arrival directions of neutrinos and UHECRs is scanned. The same events are also used in a separate search stacking the neutrino arrival directions and using a maximum likelihood approach. We assume that UHECR magnetic deflections are inversely proportional to the energy with values 3°, 6° and 9° at 100 EeV to account for the various scenarios of the magnetic field strength and UHECR charges. A similar analysis is performed on stacked UHECR arrival directions and the IceCube 4-year sample of through-going muon-track events that was optimized for neutrino point source searches.
We present the results of three searches for correlations between ultra-high energy cosmic ray events measured by Telescope Array and the Pierre Auger Observatory and high-energy neutrino candidate ...events from IceCube. Two cross-correlation analyses of ultra-high energy cosmic rays are done: one with 39 “cascades” from the IceCube “high-energy starting events” sample and the other one with 16 high-energy “tracks”. The angular separation between the arrival directions of neutrinos and UHECRs is scanned. The same events are also used in a separate search stacking the neutrino arrival directions and using a maximum likelihood approach. We assume that UHECR magnetic deflections are inversely proportional to the energy with values 3∘, 6∘ and 9∘ at 100 EeV to account for the uncertainties in the magnetic field strength and UHECR charge. A similar analysis is performed on stacked UHECR arrival directions and the IceCube 4-year sample of through-going muon-track events that was optimized for neutrino point source searches.
ABSTRACT The IceCube Collaboration has previously discovered a high-energy astrophysical neutrino flux using neutrino events with interaction vertices contained within the instrumented volume of the ...IceCube detector. We present a complementary measurement using charged current muon neutrino events where the interaction vertex can be outside this volume. As a consequence of the large muon range the effective area is significantly larger but the field of view is restricted to the Northern Hemisphere. IceCube data from 2009 through 2015 have been analyzed using a likelihood approach based on the reconstructed muon energy and zenith angle. At the highest neutrino energies between and a significant astrophysical contribution is observed, excluding a purely atmospheric origin of these events at significance. The data are well described by an isotropic, unbroken power-law flux with a normalization at neutrino energy of and a hard spectral index of . The observed spectrum is harder in comparison to previous IceCube analyses with lower energy thresholds which may indicate a break in the astrophysical neutrino spectrum of unknown origin. The highest-energy event observed has a reconstructed muon energy of which implies a probability of less than for this event to be of atmospheric origin. Analyzing the arrival directions of all events with reconstructed muon energies above no correlation with known γ-ray sources was found. Using the high statistics of atmospheric neutrinos we report the current best constraints on a prompt atmospheric muon neutrino flux originating from charmed meson decays which is below 1.06 in units of the flux normalization of the model in Enberg et al.
We report on the observation of two neutrino-induced events which have an estimated deposited energy in the IceCube detector of 1.04±0.16 and 1.14±0.17 PeV, respectively, the highest neutrino ...energies observed so far. These events are consistent with fully contained particle showers induced by neutral-current ν(e,μ,τ) (ν(e,μ,τ)) or charged-current ν(e) (ν(e)) interactions within the IceCube detector. The events were discovered in a search for ultrahigh energy neutrinos using data corresponding to 615.9 days effective live time. The expected number of atmospheric background is 0.082±0.004(stat)(-0.057)(+0.041)(syst). The probability of observing two or more candidate events under the atmospheric background-only hypothesis is 2.9×10(-3) (2.8σ) taking into account the uncertainty on the expected number of background events. These two events could be a first indication of an astrophysical neutrino flux; the moderate significance, however, does not permit a definitive conclusion at this time.
We present a measurement of the cosmic-ray spectrum above 100 PeV using the part of the surface detector of the Pierre Auger Observatory that has a spacing of 750 m. An inflection of the spectrum is ...observed, confirming the presence of the so-called
second-knee
feature. The spectrum is then combined with that of the 1500 m array to produce a single measurement of the flux, linking this spectral feature with the three additional breaks at the highest energies. The combined spectrum, with an energy scale set calorimetrically via fluorescence telescopes and using a single detector type, results in the most statistically and systematically precise measurement of spectral breaks yet obtained. These measurements are critical for furthering our understanding of the highest energy cosmic rays.
We report a measurement of the proton-air cross section for particle production at the center-of-mass energy per nucleon of 57 TeV. This is derived from the distribution of the depths of shower ...maxima observed with the Pierre Auger Observatory: systematic uncertainties are studied in detail. Analyzing the tail of the distribution of the shower maxima, a proton-air cross section of 505±22(stat)(-36)(+28)(syst) mb is found.
We describe the measurement of the depth of maximum, X{max}, of the longitudinal development of air showers induced by cosmic rays. Almost 4000 events above 10;{18} eV observed by the fluorescence ...detector of the Pierre Auger Observatory in coincidence with at least one surface detector station are selected for the analysis. The average shower maximum was found to evolve with energy at a rate of (106{-21}{+35}) g/cm{2}/decade below 10{18.24+/-0.05} eV, and (24+/-3) g/cm{2}/decade above this energy. The measured shower-to-shower fluctuations decrease from about 55 to 26 g/cm{2}. The interpretation of these results in terms of the cosmic ray mass composition is briefly discussed.
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