Motivated by the detection of a significant dipole structure in the arrival directions of ultrahigh-energy cosmic rays above 8 EeV reported by the Pierre Auger Observatory (Auger), we search for a ...large-scale anisotropy using data collected with the surface detector array of the Telescope Array Experiment (TA). With 11 years of TA data, a dipole structure in a projection of the right ascension is fitted with an amplitude of 3.3+- 1.9% and a phase of 131 +- 33 degrees. The corresponding 99% confidence-level upper limit on the amplitude is 7.3%. At the current level of statistics, the fitted result is compatible with both an isotropic distribution and the dipole structure reported by Auger.
Evidence for a large-scale supergalactic cosmic ray multiplet (arrival directions correlated with energy) structure is reported for ultra-high energy cosmic ray (UHECR) energies above 10\(^{19}\) eV ...using seven years of data from the Telescope Array (TA) surface detector and updated to 10 years. Previous energy-position correlation studies have made assumptions regarding magnetic field shapes and strength, and UHECR composition. Here the assumption tested is that, since the supergalactic plane is a fit to the average matter density of the local Large Scale Structure (LSS), UHECR sources and intervening extragalactic magnetic fields are correlated with this plane. This supergalactic deflection hypothesis is tested by the entire field-of-view (FOV) behavior of the strength of intermediate-scale energy-angle correlations. These multiplets are measured in spherical cap section bins (wedges) of the FOV to account for coherent and random magnetic fields. The structure found is consistent with supergalactic deflection, the previously published energy spectrum anisotropy results of TA (the hotspot and coldspot), and toy-model simulations of a supergalactic magnetic sheet. The seven year data post-trial significance of this supergalactic structure of multiplets appearing by chance, on an isotropic sky, is found by Monte Carlo simulation to be 4.2\(\sigma\). The ten years of data post-trial significance is 4.1\(\sigma\). Furthermore, the starburst galaxy M82 is shown to be a possible source of the TA Hotspot, and an estimate of the supergalactic magnetic field using UHECR measurements is presented.
Ultra high energy cosmic rays provide the highest known energy source in the universe to measure proton cross sections. Though conditions for collecting such data are less controlled than an ...accelerator environment, current generation cosmic ray observatories have large enough exposures to collect significant statistics for a reliable measurement for energies above what can be attained in the lab. Cosmic ray measurements of cross section use atmospheric calorimetry to measure depth of air shower maximum (\(X_{\mathrm{max}}\)), which is related to the primary particle's energy and mass. The tail of the \(X_{\mathrm{max}}\) distribution is assumed to be dominated by showers generated by protons, allowing measurement of the inelastic proton-air cross section. In this work the proton-air inelastic cross section measurement, \(\sigma^{\mathrm{inel}}_{\mathrm{p-air}}\), using data observed by Telescope Array's Black Rock Mesa and Long Ridge fluorescence detectors and surface detector array in hybrid mode is presented. \(\sigma^{\mathrm{inel}}_{\mathrm{p-air}}\) is observed to be \(520.1 \pm 35.8\)Stat. \(^{+25.0}_{-40}\)Sys.~mb at \(\sqrt{s} = 73\) TeV. The total proton-proton cross section is subsequently inferred from Glauber formalism and is found to be \(\sigma^{\mathrm{tot}}_{\mathrm{pp}} = 139.4 ^{+23.4}_{-21.3}\) Stat.\( ^{+15.0}_{-24.0}\)Sys.~mb.
We present an upper limit on the flux of ultra-high-energy down-going neutrinos for \(E > 10^{18}\ \mbox{eV}\) derived with the nine years of data collected by the Telescope Array surface detector ...(05-11-2008 -- 05-10-2017). The method is based on the multivariate analysis technique, so-called Boosted Decision Trees (BDT). Proton-neutrino classifier is built upon 16 observables related to both the properties of the shower front and the lateral distribution function.
We report an estimation of the injected mass composition of ultra-high energy cosmic rays (UHECRs) at energies higher than 10 EeV. The composition is inferred from an energy-dependent sky ...distribution of UHECR events observed by the Telescope Array surface detector by comparing it to the Large Scale Structure of the local Universe. In the case of negligible extra-galactic magnetic fields the results are consistent with a relatively heavy injected composition at E ~ 10 EeV that becomes lighter up to E ~ 100 EeV, while the composition at E > 100 EeV is very heavy. The latter is true even in the presence of highest experimentally allowed extra-galactic magnetic fields, while the composition at lower energies can be light if a strong EGMF is present. The effect of the uncertainty in the galactic magnetic field on these results is subdominant.
The surface detector (SD) of the Telescope Array (TA) experiment allows one to indirectly detect photons with energies of order \(10^{18}\) eV and higher and to separate photons from the cosmic-ray ...background. In this paper we present the results of a blind search for point sources of ultra-high energy (UHE) photons in the Northern sky using the TA SD data. The photon-induced extensive air showers (EAS) are separated from the hadron-induced EAS background by means of a multivariate classifier based upon 16 parameters that characterize the air shower events. No significant evidence for the photon point sources is found. The upper limits are set on the flux of photons from each particular direction in the sky within the TA field of view, according to the experiment's angular resolution for photons. Average 95% C.L. upper limits for the point-source flux of photons with energies greater than \(10^{18}\), \(10^{18.5}\), \(10^{19}\), \(10^{19.5}\) and \(10^{20}\) eV are \(0.094\), \(0.029\), \(0.010\), \(0.0073\) and \(0.0058\) km\(^{-2}\)yr\(^{-1}\) respectively. For the energies higher than \(10^{18.5}\) eV, the photon point-source limits are set for the first time. Numerical results for each given direction in each energy range are provided as a supplement to this paper.
The TA observatory is a hybrid detector system consisting of both a surface detector array as well as a set of fluorescence detectors. The observatory will measure the energy spectrum, anisotropy and ...composition of ultra-high energy cosmic rays. The surface detectors are being deployed and the array should be complete by the end of February, 2007. We will soon be collecting hybrid data at the Telecope Array.
The results on ultra-high-energy cosmic rays (UHECR) mass composition obtained with the Telescope Array surface detector are presented. The analysis employs the boosted decision tree (BDT) ...multivariate analysis built upon 14 observables related to both the properties of the shower front and the lateral distribution function. The multivariate classifier is trained with Monte-Carlo sets of events induced by the primary protons and iron. An average atomic mass of UHECR is presented for energies \(10^{18.0}-10^{20.0}\ \mbox{eV}\). The average atomic mass of primary particles shows no significant energy dependence and corresponds to \(\langle \ln A \rangle = 2.0 \pm 0.1 (stat.) \pm 0.44 (syst.)\). The result is compared to the mass composition obtained by the Telescope Array with \(\mbox{X}_{\mbox{max}}\) technique along with the results of other experiments. Possible systematic errors of the method are discussed.
In order to measure time correlation of primary cosmic rays, a network observation of extensive air showers started in Japan. The network as Large Area Air Shower (LAAS) group consists of nine ...air-shower-stations (seven institutes and 26.000 km
2) using the Global Positioning System (GPS). We propose an analytical procedure to extract time-limited fractal structure from time series of arrival time intervals of successive air showers and present the results of the analysis by using the network data.
Astroparticle Physics, 110 (2019) 8-14 We present the results of the search for ultra-high-energy photons with nine
years of data from the Telescope Array surface detector. A multivariate
classifier ...is built upon 16 reconstructed parameters of the extensive air
shower. These parameters are related to the curvature and the width of the
shower front, the steepness of the lateral distribution function, and the
timing parameters of the waveforms sensitive to the shower muon content. A
total number of two photon candidates found in the search is fully compatible
with the expected background. The $95\%\,$CL limits on the diffuse flux of the
photons with energies greater than $10^{18.0}$, $10^{18.5}$, $10^{19.0}$,
$10^{19.5}$ and $10^{20.0}$ eV are set at the level of $0.067$, $0.012$,
$0.0036$, $0.0013$, $0.0013~\mbox{km}^{-2}\mbox{yr}^{-1}\mbox{sr}^{-1}$
correspondingly.
