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Abstract: The Pierre Auger Observatory (Auger) in Mendoza, Argentina and the Telescope Array (TA) in Utah, USA aim at unraveling the origin and nature of Ultra-High Energy Cosmic Rays (UHECR). At present, there appear to be subtle differences between Auger and TA results and interpretations. Joint working groups have been established and have already reported preliminary findings. From an experimental standpoint, the Surface Detectors (SD) of both experiments make use of different detection processes not equally sensitive to the components of the extensive air showers making it to the ground. In particular, the muonic component of the shower measured at ground level can be traced back to the primary composition, which is critical for understanding the origin of UHECRs. In order to make direct comparisons between the SD detection techniques used by Auger and TA, a joint SD experimental research program is being developed. In the first phase, two Auger SD stations were deployed at the TA Central Laser Facility to compare station-level responses. This paper concentrates on the results obtained with the first Auger SD station (an “Auger North” design), which has been operating since October 2014. The second Auger SD station, identical to the ones being operated at Auger in Argentina (an “Auger South” design), was just deployed in June 2015. The second phase of this research program will be to co-locate six Auger North SD stations with TA stations in the field to compare event-level responses.
Found in: ključnih besedah
Keywords: Ultra-High Energy Cosmic Rays, Pierre Auger Observatory, Telescope Array, extensive air showers, secondary cosmic rays, muonic shower component, surface detectors
Published: 08.03.2016; Views: 3451; Downloads: 160
Fulltext (1,42 MB)

Found in: ključnih besedah
Keywords: Cherenkov Telescope Array (CTA), very-high energy (VHE) gamma-ray emission, star-forming regions, the Cygnus region, observational strategy optimization
Published: 11.03.2016; Views: 3504; Downloads: 228
Fulltext (585,14 KB)

Found in: ključnih besedah
Keywords: Cherenkov Telescope Array, Gamma-Ray Bursts, very-high energy (VHE) gamma-ray emission, observational strategy optimization
Published: 11.03.2016; Views: 3598; Downloads: 185
Fulltext (133,05 KB)

Abstract: We study diffuse gamma-ray emission at intermediate Galactic latitudes measured by the Fermi LAT with the aim of searching for a signal from dark matter annihilation or decay. In the absence of a robust dark matter signal, constraints are presented. We present and improve upon conservative dark matter limits obtained with no modeling of the foreground astrophysical diffuse emission. We do so, by taking into account uncertainties in several parameters which characterize conventional astrophysical emission and using a profile likelihood formalism. The resulting limits impact the range of particle masses over which dark matter thermal production in the early Universe is possible, and challenge the interpretation of the PAMELA/Fermi-LAT cosmic ray anomalies as annihilation of dark matter.
Found in: ključnih besedah
Summary of found: ...Dark matter, high-energy gamma rays...
Keywords: Dark matter, high-energy gamma rays
Published: 21.03.2016; Views: 3321; Downloads: 0
Fulltext (1,04 MB)

Abstract: The azimuthal asymmetry in the risetime of signals in Auger surface detector stations is a source of information on shower development. The azimuthal asymmetry is due to a combination of the longitudinal evolution of the shower and geometrical effects related to the angles of incidence of the particles into the detectors. The magnitude of the effect depends upon the zenith angle and state of development of the shower and thus provides a novel observable, (secθ)max, sensitive to the mass composition of cosmic rays above 3×1018  eV. By comparing measurements with predictions from shower simulations, we find for both of our adopted models of hadronic physics (QGSJETII-04 and EPOS-LHC) an indication that the mean cosmic-ray mass increases slowly with energy, as has been inferred from other studies. However, the mass estimates are dependent on the shower model and on the range of distance from the shower core selected. Thus the method has uncovered further deficiencies in our understanding of shower modeling that must be resolved before the mass composition can be inferred from (secθ)max.
Found in: ključnih besedah
Keywords: ultra-high energy cosmic rays (UHECR), UHECR mass composition, Pierre Auger Observatory, extensive air showers, Auger Surface Detector signals risetime, azimuthal symmetry
Published: 15.04.2016; Views: 4150; Downloads: 0
Fulltext (698,19 KB)