The Telescope Array (TA) collaboration has measured the energy spectrum of ultra-high energy cosmic rays with primary energies above 1.6 x 10^(18) eV. This measurement is based upon four years of ...observation by the surface detector component of TA. The spectrum shows a dip at an energy of 4.6 x 10^(18) eV and a steepening at 5.4 x 10^(19) eV which is consistent with the expectation from the GZK cutoff. We present the results of a technique, new to the analysis of ultra-high energy cosmic ray surface detector data, that involves generating a complete simulation of ultra-high energy cosmic rays striking the TA surface detector. The procedure starts with shower simulations using the CORSIKA Monte Carlo program where we have solved the problems caused by use of the "thinning" approximation. This simulation method allows us to make an accurate calculation of the acceptance of the detector for the energies concerned.
An intermediate-scale energy spectrum anisotropy has been found in the
arrival directions of ultra-high energy cosmic rays of energies above
$10^{19.2}$ eV in the northern hemisphere, using 7 years ...of data from the
Telescope Array surface detector. A relative energy distribution test is done
comparing events inside oversampled spherical caps of equal exposure, to those
outside, using the Poisson likelihood ratio. The center of maximum significance
is at $9^h$$16^m$, $45^{\circ}$. and has a deficit of events with energies
$10^{19.2}$$\leq$$E$$<$$10^{19.75}$ eV and an excess for $E$$\geq$$10^{19.75}$
eV. The post-trial probability of this energy anisotropy, appearing by chance
anywhere on an isotropic sky, is found by Monte Carlo simulation to be
$9$$\times$$10^{-5}$ ($3.74$$\sigma_{global}$).
The Telescope Array (TA) experiment, located in the western desert of Utah,USA, is designed for observation of extensive air showers from extremely high energy cosmic rays. The experiment has a ...surface detector array surrounded by three fluorescence detectors to enable simultaneous detection of shower particles at ground level and fluorescence photons along the shower track. The TA surface detectors and fluorescence detectors started full hybrid observation in March, 2008. In this article we describe the design and technical features of the TA surface detector.
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.
An intermediate-scale energy spectrum anisotropy has been found in the arrival directions of ultra-high energy cosmic rays of energies above \(10^{19.2}\) eV in the northern hemisphere, using 7 years ...of data from the Telescope Array surface detector. A relative energy distribution test is done comparing events inside oversampled spherical caps of equal exposure, to those outside, using the Poisson likelihood ratio. The center of maximum significance is at $9^h$$16^m\(, \)45^{\circ}\(. and has a deficit of events with energies \)10^{19.2}$$\leq$$E$$<$$10^{19.75}\( eV and an excess for \)E$$\geq$$10^{19.75}\( eV. The post-trial probability of this energy anisotropy, appearing by chance anywhere on an isotropic sky, is found by Monte Carlo simulation to be \)9$$\times$$10^{-5}\( (\)3.74$$\sigma_{global}$).
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