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.
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.
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 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.
The Pierre Auger Collaboration (Auger) recently reported a correlation between the arrival directions of cosmic rays with energies above 39 EeV and the flux pattern of 23 nearby starburst galaxies ...(SBGs). In this Letter, we tested the same hypothesis using cosmic rays detected by the Telescope Array experiment (TA) in the 9-year period from May 2008 to May 2017. Unlike the Auger analysis, we did not optimize the parameter values but kept them fixed to the best-fit values found by Auger, namely 9.7% for the anisotropic fraction of cosmic rays assumed to originate from the SBGs in the list and 12.9{\deg} for the angular scale of the correlations. The energy threshold we adopted is 43 EeV, corresponding to 39 EeV in Auger when taking into account the energy-scale difference between two experiments. We find that the TA data is compatible with isotropy to within 1.1{\sigma} and with the Auger result to within 1.4{\sigma}, meaning that it is not capable to discriminate between these two hypotheses.
Bursts of gamma ray showers have been observed in coincidence with downward propagating negative leaders in lightning flashes by the Telescope Array Surface Detector (TASD). The TASD is a 700~square ...kilometer cosmic ray observatory located in southwestern Utah, U.S.A. In data collected between 2014 and 2016, correlated observations showing the structure and temporal development of three shower-producing flashes were obtained with a 3D lightning mapping array, and electric field change measurements were obtained for an additional seven flashes, in both cases co-located with the TASD. National Lightning Detection Network (NLDN) information was also used throughout. The showers arrived in a sequence of 2--5 short-duration (\(\le\)10~\(\mu\)s) bursts over time intervals of several hundred microseconds, and originated at an altitude of \(\simeq\)3--5 kilometers above ground level during the first 1--2 ms of downward negative leader breakdown at the beginning of cloud-to-ground lightning flashes. The shower footprints, associated waveforms and the effect of atmospheric propagation indicate that the showers consist primarily of downward-beamed gamma radiation. This has been supported by GEANT simulation studies, which indicate primary source fluxes of $\simeq$$10^{12}\(--\)10^{14}\( photons for \)16^{\circ}$ half-angle beams. We conclude that the showers are terrestrial gamma-ray flashes (TGFs), similar to those observed by satellites, but that the ground-based observations are more representative of the temporal source activity and are also more sensitive than satellite observations, which detect only the most powerful TGFs.
