Abstract
A new analysis of the data set from the Pierre Auger Observatory provides evidence for anisotropy in the arrival directions of ultra-high-energy cosmic rays on an intermediate angular scale, ...which is indicative of excess arrivals from strong, nearby sources. The data consist of 5514 events above
with zenith angles up to 80° recorded before 2017 April 30. Sky models have been created for two distinct populations of extragalactic gamma-ray emitters: active galactic nuclei from the second catalog of hard
Fermi
-LAT sources (2FHL) and starburst galaxies from a sample that was examined with
Fermi
-LAT. Flux-limited samples, which include all types of galaxies from the
Swift
-BAT and 2MASS surveys, have been investigated for comparison. The sky model of cosmic-ray density constructed using each catalog has two free parameters, the fraction of events correlating with astrophysical objects, and an angular scale characterizing the clustering of cosmic rays around extragalactic sources. A maximum-likelihood ratio test is used to evaluate the best values of these parameters and to quantify the strength of each model by contrast with isotropy. It is found that the starburst model fits the data better than the hypothesis of isotropy with a statistical significance of 4.0
σ
, the highest value of the test statistic being for energies above
. The three alternative models are favored against isotropy with 2.7
σ
–3.2
σ
significance. The origin of the indicated deviation from isotropy is examined and prospects for more sensitive future studies are discussed.
Ultrahigh energy cosmic ray air showers probe particle physics at energies beyond the reach of accelerators. Here we introduce a new method to test hadronic interaction models without relying on the ...absolute energy calibration, and apply it to events with primary energy 6-16 EeV (E_{CM}=110-170 TeV), whose longitudinal development and lateral distribution were simultaneously measured by the Pierre Auger Observatory. The average hadronic shower is 1.33±0.16 (1.61±0.21) times larger than predicted using the leading LHC-tuned models EPOS-LHC (QGSJetII-04), with a corresponding excess of muons.
We present a detailed study of the large-scale anisotropies of cosmic rays with energies above 4 EeV measured using the Pierre Auger Observatory. For the energy bins 4, 8 EeV and E ≥ 8 EeV, the most ...significant signal is a dipolar modulation in R.A. at energies above 8 EeV, as previously reported. In this paper we further scrutinize the highest-energy bin by splitting it into three energy ranges. We find that the amplitude of the dipole increases with energy above 4 EeV. The growth can be fitted with a power law with index β = 0.79 0.19. The directions of the dipoles are consistent with an extragalactic origin of these anisotropies at all the energies considered. Additionally, we have estimated the quadrupolar components of the anisotropy: they are not statistically significant. We discuss the results in the context of the predictions from different models for the distribution of ultrahigh-energy sources and cosmic magnetic fields.
We present the first measurement of the fluctuations in the number of muons in extensive air showers produced by ultrahigh energy cosmic rays. We find that the measured fluctuations are in good ...agreement with predictions from air shower simulations. This observation provides new insights into the origin of the previously reported deficit of muons in air shower simulations and constrains models of hadronic interactions at ultrahigh energies. Our measurement is compatible with the muon deficit originating from small deviations in the predictions from hadronic interaction models of particle production that accumulate as the showers develop.
We report a measurement of the energy spectrum of cosmic rays for energies above 2.5 × 1018 eV based on 215,030 events recorded with zenith angles below 60°. A key feature of the work is that the ...estimates of the energies are independent of assumptions about the unknown hadronic physics or of the primary mass composition. The measurement is the most precise made hitherto with the accumulated exposure being so large that the measurements of the flux are dominated by systematic uncertainties except at energies above 5 × 1019 eV. The principal conclusions are (1) The flattening of the spectrum near 5 × 1018 eV, the so-called "ankle," is confirmed. (2) The steepening of the spectrum at around 5 × 1019 eV is confirmed. (3) A new feature has been identified in the spectrum: in the region above the ankle the spectral index γ of the particle flux ( ∝ E−γ ) changes from 2.51 ± 0.03 ( stat ) ± 0.05 ( syst ) to 3.05 ± 0.05 ( stat ) ± 0.10 ( syst ) before changing sharply to 5.1 ± 0.3 ( stat ) ± 0.1 ( syst ) above 5 × 1019 eV. (4) No evidence for any dependence of the spectrum on declination has been found other than a mild excess from the Southern Hemisphere that is consistent with the anisotropy observed above 8 × 1018 eV.
We present measurements of the large-scale cosmic-ray (CR) anisotropies in R.A., using data collected by the surface detector array of the Pierre Auger Observatory over more than 14 yr. We determine ...the equatorial dipole component, , through a Fourier analysis in R.A. that includes weights for each event so as to account for the main detector-induced systematic effects. For the energies at which the trigger efficiency of the array is small, the "east-west" method is employed. Besides using the data from the array with detectors separated by 1500 m, we also include data from the smaller but denser subarray of detectors with 750 m separation, which allows us to extend the analysis down to ∼0.03 EeV. The most significant equatorial dipole amplitude obtained is that in the cumulative bin above 8 EeV, %, which is inconsistent with isotropy at the 6 level. In the bins below 8 EeV, we obtain 99% CL upper bounds on d at the level of 1%-3%. At energies below 1 EeV, even though the amplitudes are not significant, the phases determined in most of the bins are not far from the R.A. of the Galactic center, at GC = −94°, suggesting a predominantly Galactic origin for anisotropies at these energies. The reconstructed dipole phases in the energy bins above 4 EeV point instead to R.A. that are almost opposite to the Galactic center one, indicative of an extragalactic CR origin.
We report a measurement of the energy spectrum of cosmic rays above 2.5 × 1018 eV based on 215 030 events. New results are presented: at about 1.3 × 1019 eV , the spectral index changes from 2.51 ± ...0.03 (stat) ± 0.05 (syst) to 3.05 ± 0.05 (stat) ± 0.10 (syst), evolving to 5.1 ± 0.3 (stat) ± 0.1 (syst) beyond 5 × 1019 eV, while no significant dependence of spectral features on the declination is seen in the accessible range. These features of the spectrum can be reproduced in models with energy-dependent mass composition. The energy density in cosmic rays above 5 × 1018 eV is 5.66 ± 0.03 (stat) ± 1.40 (syst) × 1053 erg Mpc−3.
Abstract
Results of a search for ultra-high-energy neutrinos with the Pierre Auger Observatory from the direction of the blazar TXS 0506+056 are presented. They were obtained as part of the follow-up ...that stemmed from the detection of high-energy neutrinos and gamma rays with IceCube, Fermi-LAT, MAGIC, and other detectors of electromagnetic radiation in several bands. The Pierre Auger Observatory is sensitive to neutrinos in the energy range from 100 PeV to 100 EeV and in the zenith-angle range from
θ
= 60° to
θ
= 95°, where the zenith angle is measured from the vertical direction. No neutrinos from the direction of TXS 0506+056 have been found. The results were analyzed in three periods: one of 6 months around the detection of IceCube-170922 A, coinciding with a flare period of TXS 0506+056, a second one of 110 days during which the IceCube collaboration found an excess of 13 neutrinos from a direction compatible with TXS 0506+056, and a third one from 2004 January 1 up to 2018 August 31, over which the Pierre Auger Observatory has been taking data. The sensitivity of the Observatory is addressed for different spectral indices by considering the fluxes that would induce a single expected event during the observation period. For indices compatible with those measured by the IceCube collaboration the expected number of neutrinos at the Observatory is well below one. Spectral indices as hard as 1.5 would have to apply in this energy range to expect a single event to have been detected.
We present a new method for probing the hadronic interaction models at ultrahigh energy and extracting details about mass composition. This is done using the time profiles of the signals recorded ...with the water-Cherenkov detectors of the Pierre Auger Observatory. The profiles arise from a mix of the muon and electromagnetic components of air showers. Using the risetimes of the recorded signals, we define a new parameter, which we use to compare our observations with predictions from simulations. We find, first, inconsistencies between our data and predictions over a greater energy range and with substantially more events than in previous studies. Second, by calibrating the new parameter with fluorescence measurements from observations made at the Auger Observatory, we can infer the depth of shower maximum Xmax for a sample of over 81,000 events extending from 0.3 to over 100 EeV. Above 30 EeV, the sample is nearly 14 times larger than what is currently available from fluorescence measurements and extending the covered energy range by half a decade. The energy dependence of ⟨Xmax⟩ is compared to simulations and interpreted in terms of the mean of the logarithmic mass. We find good agreement with previous work and extend the measurement of the mean depth of shower maximum to greater energies than before, reducing significantly the statistical uncertainty associated with the inferences about mass composition.
Two of the biggest challenges for future HEP experiments at hadron colliders are triggering and track reconstruction of high-multiplicity events, where collisions have multiple primary vertices. The ...highly-non-linear scaling of computing power required for these tasks encourages the adoption of non-traditional, specialized architectures. Amongst them, the “artificial retina” approach, inspired by the architecture of the vision system in the living brain, promises large efficiency of hardware utilization, low-power and low-latency when implemented in state-of-art FPGA devices.
The INFN-RETINA project has been a 3-year effort dedicated to investigate the potential of that approach in a real-time tracking processor at Level-0 of the LHC HEP experiments. We present results from studies performed on a prototype system capable of carrying out track reconstruction in a generic 6-layer silicon-strip detector with sub-μs latency at an event rate in excess of 30 MHz, and how a large-scale system can be implemented on multiple boards interconnected with high-speed optical links. Possible applications to real experimental environments will be also discussed.
PDF
