Since 2007, the Telescope Array (TA) experiment, based in Utah, USA, has been observing ultra high energy cosmic rays to understand their origins. The experiment includes a surface detector (SD) ...array and three fluorescence detector (FD) stations. The FD stations, installed surrounding the SD array, measure the air fluorescence light emitted from extensive air showers (EASs) for precise determination of their energies and species. The detectors employed at one of the three FD stations were relocated from the High Resolution Fly's Eye (HiRes) experiment. At the other two stations, newly designed detectors were constructed for the TA experiment. An FD consists of a primary mirror and a camera equipped with photomultiplier tube pixels. To obtain the EAS parameters with high accuracy, understanding the FD optical characteristics is important. In this paper, we report the characteristics and installation of the new FDs and the performances of the FD components. The results of the monitored mirror reflectance during the observation time are also described in this report.
The atmospheric monitoring is very important for the observation of air shower by air fluorescence technique. In the Telescope Array (TA) experiment, LIDAR (Light Detection And Ranging) system and ...CLF (Central Laser Facility) system have been used for the measurement of atmospheric transparency. The LIDAR system is located in the southeast of TA site. The CLF is located in the center of the TA site. The usefulness of the CLF and LIDAR systems is demonstrated by analyzing the time variation of atmospheric transparency with the systems. The two atmospheric monitor systems are complementary. Therefore, monitoring efficiency is advanced by a new LIDAR system that was installed at CLF system. Clouds are observed with CCD camera, IR camera and eye scan visual check. In addition, we have also measured atmospheric parameters at the ground level using several weather systems.
The effects of the surface oxidation on the helium desorption and retention behaviors of vanadium alloy were investigated. V–4Cr–4Ti alloy, which was thermally oxidized at 873K for 15min with 0.05Pa, ...was irradiated by helium ions with energy of 5keV at room temperature. Then, the helium desorption and retention behaviors were evaluated using a technique of thermal desorption spectroscopy. The changes in surface structures by the irradiation were also evaluated. Helium desorption behavior in low temperature region were significantly changed by the oxidation. Helium desorption around 700K became large for the oxidized sample. The amount of retained helium and the blister size in the oxidized sample were smaller than of those in the non-oxidized one. These results indicate that the surface oxidation significantly affects the helium retention and desorption behaviors of the vanadium alloy.
Retention and desorption behaviors of helium in oxidized and non-oxidized V–4Cr–4Ti alloy samples were investigated after helium ion irradiation at room temperature using a thermal desorption ...spectroscopy. The ion energy and fluence were 5
keV and (0.5–10)
×
10
21
He/m
2, respectively. An oxidized layer with a thickness of 100
nm was prepared by thermal oxidation. The surface density of blisters produced by helium ion irradiation in the oxidized sample was lower than that in the non-oxidized one. The helium desorption behavior depended significantly on the fluence. In the lower fluence regime, the retained helium desorbed mainly at around 1300
K in both samples. As fluence increased, several desorption peaks appeared in the low temperature region in both samples. However, the peak temperatures were different. The amount of helium retained in the oxidized sample was lower than that in the non-oxidized sample.
The surface detector array of the Telescope Array experiment Abu-Zayyad, T.; Aida, R.; Anderson, R. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
10/2012, Letnik:
689
Journal Article
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Odprti dostop
The Telescope Array (TA) experiment, located in the western desert of Utah, USA, is designed for the 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.
The Telescope Array (TA) collaboration has measured the energy spectrum of ultra-high energy cosmic rays (UHECRs) with primary energies above 1.6 x 10 super(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 super(18) eV and a steepening at 5.4 x 10 super(19) eV which is consistent with the expectation from the GZK cutoff. We present the results of a technique, new to the analysis of UHECR surface detector data, that involves generating a complete simulation of UHECRs 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.
We study the anisotropy of Ultra-High Energy Cosmic Ray (UHECR) events collected by the Telescope Array (TA) detector in the first 40 months of operation. Following earlier studies, we examine event ...sets with energy thresholds of 10 EeV, 40 EeV, and 57 EeV. We find that the distributions of the events in right ascension and declination are compatible with an isotropic distribution in all three sets. We then compare with previously reported clustering of the UHECR events at small angular scales. No significant clustering is found in the TA data. We then check the events with E > 57 EeV for correlations with nearby active galactic nuclei. No significant correlation is found. Finally, we examine all three sets for correlations with the large-scale structure (LSS) of the universe. We find that the two higher-energy sets are compatible with both an isotropic distribution and the hypothesis that UHECR sources follow the matter distribution of the universe (the LSS hypothesis), while the event set with E > 10 EeV is compatible with isotropy and is not compatible with the LSS hypothesis at 95% CL unless large deflection angles are also assumed. We show that accounting for UHECR deflections in a realistic model of the Galactic magnetic field can make this set compatible with the LSS hypothesis.
We search for correlations between the positions of extragalactic objects and the arrival directions of ultra-high energy cosmic rays (UHECRs) with primary energy E > or =, slanted 40 EeV as observed ...by the surface detector array of the Telescope Array (TA) experiment during the first 40 months of operation. We examine several public astronomical object catalogs, including the Veron-Cetty and Veron catalog of active galactic nuclei. We count the number of TA events correlated with objects in each catalog as a function of three parameters: the maximum angular separation between a TA event and an object, the minimum energy of the events, and the maximum redshift of the objects. We determine the combination of these parameters that maximizes the correlations, and we calculate the probability of having the same levels of correlations from an isotropic distribution of UHECR arrival directions. No statistically significant correlations are found when penalties for scanning over the above parameters and for searching in several catalogs are taken into account.
► We show the first physics results from the Middle Drum detector for Telescope Array. ► We quantify a spectral and energy scale comparison between Middle Drum and HiRes-1. ► We quantify a comparison ...between Middle Drum monocular and hybrid observation. ► We justify the transfer of the HiRes energy scale to all of Telescope Array.
The Telescope Array’s Middle Drum fluorescence detector was instrumented with telescopes refurbished from the High Resolution Fly’s Eye’s HiRes-1 site. The data observed by Middle Drum in monocular mode was analyzed via the HiRes-1 profile-constrained geometry reconstruction technique and utilized the same calibration techniques enabling a direct comparison of the energy spectra and energy scales between the two experiments. The spectrum measured using the Middle Drum telescopes is based on a three-year exposure collected between December 16, 2007 and December 16, 2010. The calculated difference between the spectrum of the Middle Drum observations and the published spectrum obtained by the data collected by the HiRes-1 site allows the HiRes-1 energy scale to be transferred to Middle Drum. The HiRes energy scale is applied to the entire Telescope Array by making a comparison between Middle Drum monocular events and hybrid events that triggered both Middle Drum and the Telescope Array’s scintillator ground array.
We present a measurement of the energy spectrum of ultra-high-energy cosmic rays performed by the Telescope Array experiment using monocular observations from its two new FADC-based fluorescence ...detectors. After a short description of the experiment, we describe the data analysis and event reconstruction procedures. Since the aperture of the experiment must be calculated by Monte Carlo simulation, we describe this calculation and the comparisons of simulated and real data used to verify the validity of the aperture calculation. Finally, we present the energy spectrum calculated from the merged monocular data sets of the two FADC-based detectors, and also the combination of this merged spectrum with an independent, previously published monocular spectrum measurement performed by Telescope Array’s third fluorescence detector T. Abu-Zayyad et al., The energy spectrum of Telescope Array’s middle drum detector and the direct comparison to the high resolution fly’s eye experiment, Astroparticle Physics 39 (2012) 109-119, http://dx.doi.org/10.1016/j.astropartphys.2012.05.012, Available from: <arXiv:1202.5141>. This combined spectrum corroborates the recently published Telescope Array surface detector spectrum T. Abu-Zayyad, et al., The cosmic-ray energy spectrum observed with the surface detector of the Telescope Array experiment, ApJ 768 (2013) L1, http://dx.doi.org/10.1088/2041-8205/768/1/L1, Available from: <arXiv:1205.5067> with independent systematic uncertainties.
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