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91.
Analysis of TAx4 hybrid trigger and events
S. Kim, Jon Paul Lundquist, 2022, published scientific conference contribution

Abstract: The Telescope Array is the largest ultra-high energy cosmic ray hybrid detector in the Northern hemisphere. While the TAx4 Surface Detector (TAx4 SD) has a duty cycle of ~ 100%, it should be noted that the TAx4 Fluorescence Detector (TAx4 FD) observes the full longitudinal profile of the cosmic ray air showers and therefore is able to determine their energies more accurately than TAx4 SD. In addition, observing cosmic rays in hybrid mode (“hybrid events”) has several advantages. Events seen in hybrid mode by the TAx4 FD and SD are used to establish the energy scale of the TAx4 SD. Moreover, the FD longitudinal profile is used to determine the mass composition of the primary comic ray particles, when the event geometries are well constrained by FD and SD measurements simultaneously. Despite large differences in the TAx4 SD/FD stand-alone performances, both detector types complement each other in measuring important physical quantities. Since August 2019, direction, energy, and Xmax can be obtained from reconstructing hybrid events. In this poster, preliminary analysis of TAx4 hybrid trigger and TAx4 hybrid events will be presented with focus on energy and Xmax observations.
Keywords: Telescope Array, TAx4, indirect detection, hybrid detection, hybrid trigger, ground array, fluorescence detection, ultra-high energy, cosmic rays, energy, Xmax
Published in RUNG: 03.10.2023; Views: 498; Downloads: 6
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92.
Large-scale and multipolar anisotropies of cosmic rays detected at the Pierre Auger Observatory with energies above 4 EeV
R. de Almeida, Andrej Filipčič, Jon Paul Lundquist, Samo Stanič, Serguei Vorobiov, Danilo Zavrtanik, Marko Zavrtanik, Lukas Zehrer, 2022, published scientific conference contribution

Abstract: More than half a century after the discovery of ultra-high energy cosmic rays (UHECRs), their origin is still an open question. The study of anisotropies in the arrival directions of such particles is an essential ingredient to solve this puzzle. We update our previous analysis of large-scale anisotropies observed by the Pierre Auger Observatory using the latest data collected before the AugerPrime upgrade. We select events with zenith angles up to 80 degrees, implying a sky coverage of 85%, and energies above 4 EeV, for which the surface detector of the Observatory is fully efficient. Dipolar and quadrupolar amplitudes are evaluated through a combined Fourier analysis of the event count rate in right ascension and azimuth. The analysis is performed in three energy bins with boundaries at 4, 8, 16 and 32 EeV and two additional cumulative bins with energies above 8 and 32 EeV. The most significant signal is a dipolar modulation in right ascension for energies above 8 EeV, as previously reported, with statistical significance of 6.6σ. Additionally, we report the measurements of the angular power spectrum for the same energy bins with the same dataset.
Keywords: Pierre Auger Observatory, indirect detection, surface detection, ground array, ultra-high energy, cosmic rays, anisotropy, dipole, quadropole, angular power spectrum, inclined showers
Published in RUNG: 03.10.2023; Views: 572; Downloads: 4
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93.
Joint analysis of the energy spectrum of ultra-high-energy cosmic rays as measured at the Pierre Auger Observatory and the Telescope Array
Y. Tsunesada, Andrej Filipčič, Jon Paul Lundquist, Samo Stanič, Serguei Vorobiov, Danilo Zavrtanik, Marko Zavrtanik, Lukas Zehrer, 2022, published scientific conference contribution

Abstract: The measurement of the energy spectrum of ultra-high-energy cosmic rays (UHECRs) is of crucial importance to clarify their origin and acceleration mechanisms. The Pierre Auger Observatory in Argentina and the Telescope Array (TA) in the US have reported their measurements of UHECR energy spectra observed in the southern and northern hemisphere, respectively. The region of the sky accessible to both Observatories ([−15,+24] degrees in declination) can be used to cross-calibrate the two spectra. The Auger-TA energy spectrum working group was organized in 2012 and has been working to understand the uncertainties in energy scale in both experiments, their systematic differences, and differences in the shape of the spectra. In previous works, we reported that there was an overall agreement of the energy spectra measured by the two observatories below 10 EeV while at higher energies, a remaining significant difference was observed in the common declination band. We revisit this issue to understand its origin by examining the systematic uncertainties, statistical effects, and other possibilities. We will also discuss the differences in the spectra in different declination bands and a new feature in the spectrum recently reported by the Auger Collaboration.
Keywords: Telescope Array, Pierre Auger Observatory, indirect detection, surface detection, ground array, ultra-high energy, cosmic rays, energy spectrum, anisotropy, declination dependence, fully sky
Published in RUNG: 02.10.2023; Views: 516; Downloads: 6
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94.
Telescope Array Combined Fit to Cosmic Ray Spectrum and Composition
D. Bergman, Jon Paul Lundquist, 2022, published scientific conference contribution

Abstract: We present the result of fits of an astrophysical model of UHECR sources to the energy spectrum measured using the Telescope Array (TA) surface detectors and the composition data measured by TA fluorescence detectors in stereo mode. The astrophysical model consists of identical sources, uniformly distributed with a density which evolves with age, where groups of nuclei with varying fractions are accelerated producing a power law source with a rigidity-dependent cutoff. The model includes the propagation effects of photo-pion production, photo-nuclear disintegration and general energy loss from universal expansion. Comparison of model data with detector data in both the energy and the Xmax distributions is done via a forward-folding description of detector effects. A prediction of the cosmogenic neutrino flux at Earth resulting from the cosmic rays produced in the model with these fit values is also presented. The predicted flux is considerably higher than other similar fits to Auger data have previously predicted.
Keywords: Telescope Array, indirect detection, stereo detection, fluorescence detection, ultra-high energy, cosmic rays, energy spectrum, composition, combined fit, cosmogenic neutrinos, multimessenger
Published in RUNG: 02.10.2023; Views: 641; Downloads: 5
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95.
Telescope Array 10-Year Monocular Spectrum Measurement
D. Bergman, Jon Paul Lundquist, 2022, published scientific conference contribution

Abstract: Telescope Array (TA) is the largest cosmic ray detector in the northern hemisphere. We present a measurement of the cosmic ray energy spectrum for energies above 10^17.5 eV using fluorescence telescopes in monocular mode. A novel weather classification scheme using machine learning was used to select data parts with good weather to ensure the quality of the fluorescence data. The data from the Black Rock Mesa (BR) and Long Ridge (LR) fluorescence telescope stations were analysed separately in monocular mode, with the calculated fluxes combined into a single spectrum. The 10-year monocular combined cosmic ray energy spectrum is in excellent agreement with previous measurements from the northern hemisphere. We present fits of the combined spectrum to a series of broken power law models. A thrice-broken power law is observed to be the best fit considering the Poisson deviance per degrees of freedom. The three breaks suggest an additional feature of the spectrum between the previously observed Ankle at 10^18.7 eV and the GZK suppression at 10^19.8 eV.
Keywords: Telescope Array, indirect detection, fluorescence detection, ultra-high energy, cosmic rays, energy spectrum, composition, machine learning, weather classification
Published in RUNG: 02.10.2023; Views: 572; Downloads: 5
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96.
Constraining Lorentz Invariance Violation using the muon content of extensive air showers measured at the Pierre Auger Observatory
C. Trimarelli, Andrej Filipčič, Jon Paul Lundquist, Samo Stanič, Serguei Vorobiov, Danilo Zavrtanik, Marko Zavrtanik, Lukas Zehrer, 2022, published scientific conference contribution

Abstract: Lorentz symmetry requires the space-time structure to be the same for all observers, but, on the other hand, various quantum gravity theories suggest that it may be violated when approaching the Planck scale. Even a small violation of Lorentz Invariance (LI) could easily affect the Ultra High Energy Cosmic Rays (UHECRs) propagation on a cosmological scale. Moreover, at the extreme energies, like those available in the collision of UHECRs with atmosphere, one should also expect a change in the interactions and, therefore, in the development of extensive air showers. For the first time, this effect has been studied using the muon content of air showers measured at the Pierre Auger Observatory. After having introduced Lorentz Invariance Violation (LIV) as a perturbation term in the single particle dispersion relation, a library of simulated showers with different energies, primary particles and LIV strengths has been produced. Leading to a change in the energy threshold of particle decays, the modification of the energy-momentum relation allows hadronic interactions of neutral pions that contribute to the growth of the hadronic cascade. As a consequence, an increase in the number of muons and a decrease in their intrinsic fluctuations are expected. Comparing the Monte Carlo expectations with the muon fluctuation measurements from the Pierre Auger Observatory, limits on LIV parameters have been derived and presented in this contribution.
Keywords: Pierre Auger Observatory, indirect detection, surface detection, ground array, ultra-high energy, cosmic rays, muons, air showers, Lorentz violation
Published in RUNG: 02.10.2023; Views: 594; Downloads: 6
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97.
Recent measurement of the Telescope Array energy spectrum and observation of the shoulder feature in the Northern Hemisphere
D. Ivanov, Jon Paul Lundquist, 2022, published scientific conference contribution

Abstract: The Telescope Array (TA) is a hybrid cosmic ray detector deployed in 2007 in Millard County, Utah, USA, which consists of a surface detector of 507 plastic scintillation counters spanning a 700 km^2 area on the ground that is overlooked by three fluorescence detector stations. The High Resolution Fly's Eye (HiRes) experiment is a predecessor of TA, which consisted of two fluorescence detector stations operating from 1997 until 2006 from Dugway Proving Ground, Utah, USA, and which was the the first cosmic ray experiment with sufficient resolution and exposure to successfully observe the Greisen–Zatsepin–Kuzmin (GZK) suppression at 10^19.75 eV. In this work, we present an updated TA energy spectrum result and a joint fit of independent spectrum measurements by the TA surface detector, TA fluorescence detector, and HiRes fluorescence detector to a broken power law function, which exhibits the ankle, GZK suppression, and the new shoulder feature initially seen by the Pierre Auger Observatory in the Southern Hemisphere. HiRes and TA observe the shoulder feature in the Northern Hemisphere at 10^19.25 eV, with a statistical significance of 5.3 standard deviations.
Keywords: Telescope Array, High Resolution Fly's Eye, HiRes, indirect detection, hybrid detection, ground array, fluorescence detection, ultra-high energy, cosmic rays, energy spectrum, GZK
Published in RUNG: 02.10.2023; Views: 449; Downloads: 6
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98.
Monocular Energy Spectrum using the TAx4 Fluorescence Detector
M. Potts, Jon Paul Lundquist, 2022, published scientific conference contribution

Abstract: Following the evidence for a hotspot in the arrival directions of the highest energy cosmic rays, the Telescope Array (TA) Experiment undertook the TAx4 upgrade to expand the area of our Surface Detectors (SD) by a factor of 4 and have added new Fluorescence Detector (FD) stations to view over the new SD arrays. Currently, TAx4 consists of 12 FDs and 257 SDs, of a planned 500, at a spacing of 2.08 km spread over two sites. TAx4 North (4 FDs), completed in 2018, views over the northern wing of the new SD, and TAx4 South (8 FDs), completed in 2019, views over the southern wing. Both FD sites are in routine observation, with data being taken remotely at the TAx4 South site. In this work, we will report on the performance of the TAx4 FD, showing data/MC comparisons. We will present a preliminary monocular energy spectrum for the TAx4 fluorescence detector and the progress of the hybrid analysis.
Keywords: Telescope Array, TAx4, indirect detection, fluorescence detection, ultra-high energy, cosmic rays, energy spectrum
Published in RUNG: 02.10.2023; Views: 464; Downloads: 4
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99.
Anisotropy search in the Ultra High Energy Cosmic Ray Spectrum in the Northern Hemisphere using latest data obtained with Telescope Array surface detector
T. Nonaka, Jon Paul Lundquist, 2022, published scientific conference contribution

Abstract: The Telescope Array (TA) experiment is located in the western desert of Utah, USA and observes ultra-high energy cosmic rays in the northern hemisphere. At the energies, the shape of the cosmic ray energy spectrum carries information of the source distribution. We present the search for differences in spectrum shape in different parts of the sky using latest data of TA surface detector (SD) data. From this study, we observe an apparent enhancement in the region of the northern sky that contain nearby objects, such as the super-galactic plane. Details of this analysis will be presented.
Keywords: Telescope Array, indirect detection, surface detection, ground array, ultra-high energy, cosmic rays, energy spectrum, anisotropy
Published in RUNG: 02.10.2023; Views: 520; Downloads: 5
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100.
Insight Into Lightning Initiation via Downward Terrestrial Gamma-ray Flash Observations at Telescope Array
J. Remington, Jon Paul Lundquist, 2022, published scientific conference contribution

Abstract: Due to the difficulty of direct measurement of the thunderstorm environment, in particular the electric field strengths, the initial stages of lightning breakdown remain mysterious. The 1994 discovery of Terrestrial Gamma-ray Flashes (TGFs) and their implications for megaVolt potentials within thunderclouds has proved to be a valuable source of information about the breakdown process. The Telescope Array Surface Detector (TASD) --- a 700 km^2 scintillator array in Western Utah, U.S.A --- coupled with a lightning mapping array, fast sferic (field change) sensor and broadband interferometer, has provided unique insight into the properties of this energetic radiation and of lightning initiation in general. In particular, microsecond-scale timing comparisons have clearly established that downward TGFs occur during strong initial breakdown pulses (IBPs) of downward negative cloud-to-ground and intracloud flashes. In turn, the IBPs are produced by streamer-based fast negative breakdown. Investigations into downward TGFs with the TASD have significantly evolved with recent upgrades to lightning instrumentation. A second state-of-the-art broadband interferometer allows high-resolution stereo observation of lightning development. A high-speed optical video camera, set to be deployed in Spring 2021, will allow simultaneous observation of the visual component of lightning responsible for TGF production. Finally, a suite of ground based static electric field mills will provide new information on the large-scale properties of the thunderstorms in which downward TGFs arise. In this talk, we present the most recent TGF observations from the Telescope Array.
Keywords: Telescope Array, ground array, ultra-high energy, cosmic rays, photons, terrestrial gamma-ray flashes, gamma-rays, lightning
Published in RUNG: 02.10.2023; Views: 525; Downloads: 6
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