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42. Composition Measurements via Depth of Airshower Maximum at the Telescope ArrayJon Paul Lundquist, W. Hanlon, 2018, objavljeni znanstveni prispevek na konferenci Opis: Telescope Array (TA) was designed to answer important questions about the UHECR flux with energies above 10^17 eV such as spectrum, arrival direction, and mass composition. Because the UHECR flux is rapidly falling in this energy region, TA’s large exposure makes it one of the few experiments in the world that can adequately explore these issues. Composition is particularly difficult to measure because mass can not be measured directly due to the low flux. TA’s multiple methods of observing UHECR induced air showers will be explained, as well as how composition can be measured by these methods. Good agreement among the different measurement techniques is found leading to greater confidence in measuring UHECR mass composition and a way to test and understand TA systematic uncertainties.
Ključne besede: UHECR, cosmic rays, composition
Objavljeno v RUNG: 29.04.2020; Ogledov: 2601; Prenosov: 103
 Celotno besedilo (758,27 KB) |
43. Telescope Array Composition SummaryW. Hanlon, Jon Paul Lundquist, 2018, objavljeni znanstveni prispevek na konferenci Opis: Ultra high energy cosmic ray (UHECR) chemical composition is
important to resolving questions about the locations of UHECR
sources and propagation models. Because composition can only be
deduced by a process of statistical inference via the observation of air shower maxima (Xmax), UHECR observatories with large data
collection rates must be employed to reduce statistical
fluctuations. Telescope Array (TA), the largest cosmic ray
observatory in the Northern Hemisphere, is designed to answer the
question of UHECR composition, as well as other important features
of cosmic ray flux, by combining a large array of over 500
scintillation surface detectors spread over 700 km^2, and three
fluorescence detector stations overlooking the array. With eight
years of data recorded, results of the measurements of UHECR
composition will be presented. UHECR composition is traditionally
measured by comparing the first and second moments of the
distributions of shower maxima, which evolves with energy, between
data and simulations. Reducing statistical fluctuations in the data
helps to distinguish between different primary elements in the
flux. In the current generation of cosmic ray observatories, UHECR
data sets are large enough, and statistical uncertainties are now
small enough, that we can safely distinguish between very light
primary source flux (i.e., protons) and heavy flux (i.e.,
iron). Reducing systematic uncertainties is also important though,
since large systematic shifts in air shower maxima will influence
the interpretation of the data when compared to models. TA therefore employs different methods of measuring Xmax, including stereo air fluorescence, air fluorescence-surface counter hybrid, and a new technique using only surface counters. Updated results of TA hybrid composition among the different methods are presented using up to eight years of data. Agreement among all TA hybrid composition results are shown as well as detailed systematic errors which can be further explored by comparing composition results of the different measurement methods. Comparison of TA Xmax data are
compared to different composition models as well.
Ključne besede: UHECR, Cosmic rays, composition
Objavljeno v RUNG: 29.04.2020; Ogledov: 2511; Prenosov: 83
Celotno besedilo (499,33 KB) |
44. Depth of Ultra High Energy Cosmic Ray Induced Air Shower Maxima Measured by the Telescope Array Black Rock and Long Ridge FADC Fluorescence Detectors and Surface Array in Hybrid ModeR.U. Abbasi, Jon Paul Lundquist, 2018, izvirni znanstveni članek Opis: The Telescope Array (TA) observatory utilizes fluorescence detectors and surface detectors (SDs) to observe air showers produced by ultra high energy cosmic rays in Earth's atmosphere. Cosmic-ray events observed in this way are termed hybrid data. The depth of air shower maximum is related to the mass of the primary particle that generates the shower. This paper reports on shower maxima data collected over 8.5 yr using the Black Rock Mesa and Long Ridge fluorescence detectors in conjunction with the array of SDs. We compare the means and standard deviations of the observed Xmax distributions with Monte Carlo Xmax distributions of unmixed protons, helium, nitrogen, and iron, all generated using the QGSJet II-04 hadronic model. We also perform an unbinned maximum likelihood test of the observed data, which is subjected to variable systematic shifting of the data Xmax distributions to allow us to test the full distributions, and compare them to the Monte Carlo to see which elements are not compatible with the observed data. For all energy bins, QGSJet II-04 protons are found to be compatible with TA hybrid data at the 95% confidence level after some systematic Xmax shifting of the data. Three other QGSJet II-04 elements are found to be compatible using the same test procedure in an energy range limited to the highest energies where data statistics are sparse.
Ključne besede: acceleration of particles, astrochemistry, astroparticle physics, cosmic rays, elementary particles, UHECR, composition
Objavljeno v RUNG: 27.04.2020; Ogledov: 3148; Prenosov: 0
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45. Mass composition of ultrahigh-energy cosmic rays with the Telescope Array Surface Detector dataR.U. Abbasi, Jon Paul Lundquist, 2019, izvirni znanstveni članek Opis: The results on ultrahigh-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 eV. The average atomic mass of primary particles shows no significant energy dependence and corresponds to ⟨lnA⟩=2.0±0.1 (stat.)±0.44(syst.). The result is compared to the mass composition obtained by the Telescope Array with Xmax technique along with the results of other experiments. Possible systematic errors of the method are discussed.
Ključne besede: UHECR, Cosmic rays, composition
Objavljeno v RUNG: 27.04.2020; Ogledov: 2781; Prenosov: 0
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46. Study of Ultra-High Energy Cosmic Ray composition using Telescope Array’s Middle Drum detector and surface array in hybrid modeR.U. Abbasi, Jon Paul Lundquist, 2015, izvirni znanstveni članek Opis: Previous measurements of the composition of Ultra-High Energy Cosmic Rays (UHECRs) made by the High Resolution Fly’s Eye (HiRes) and Pierre Auger Observatory (PAO) are seemingly contradictory, but utilize different detection methods, as HiRes was a stereo detector and PAO is a hybrid detector. The five year Telescope Array (TA) Middle Drum hybrid composition measurement is similar in some, but not all, respects in methodology to PAO, and good agreement is evident between data and a light, largely protonic, composition when comparing the measurements to predictions obtained with the QGSJetII-03 and QGSJet-01c models. These models are also in agreement with previous HiRes stereo measurements, confirming the equivalence of the stereo and hybrid methods. The data is incompatible with a pure iron composition, for all models examined, over the available range of energies. The elongation rate and mean values of are in good agreement with Pierre Auger Observatory data. This analysis is presented using two methods: data cuts using simple geometrical variables and a new pattern recognition technique.
Ključne besede: Ultra-High Energy Cosmic Rays, Cosmic ray composition, Atmospheric fluorescence, Extensive air shower array, Hybrid, Telescope Array
Objavljeno v RUNG: 24.04.2020; Ogledov: 3028; Prenosov: 0
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47. Eenergy Anisotropies of Proton-like Ultra-High Energy Cosmic RaysJon Paul Lundquist, doktorska disertacija Opis: Evidence of a number of interrelated energy dependent intermediate-scale anisotropies have been found in the arrival directions of proton-like ultra-high energy cosmic rays (UHECR) using 7 years of Telescope Array (TA) data. These are found using analysis techniques that have been developed for this dissertation. Using surface detector (SD) data the reported TA “Hotspot” excess, E≥10^19.75 eV, is found to correspond to a deficit, or “Coldspot,” of events for 10^19.1≤E<10^19.75 eV at 142◦R.A., 40◦ Dec. The global post-trial significance of this Hot/Coldspot event density asymmetry is found to be 5.1σ (p = 1.56 × 10−7). This Hot/Coldspot feature is the combination, at the same location, of an energy spectrum anisotropy with a 3.74σ significance for energies E≥10^19.2 eV and an energy-distance correlation with a 3.34σ significance for energies E≥1019.3 eV. The UHECR Hotspot alone is analyzed using a new kernel density estimation (KDE) anisotropy method and found to have a 3.65σ significance (E≥1019.75 eV). These features suggest energy dependent magnetic deflection of UHECR. The composition of UHECR primary particles is also studied using a new “Quality Factor Analysis” pattern recognition event selection for fluorescence detectors (FD). This minimizes the energy dependence of the resolution of extensive air shower (EAS) Xmax depth. Also, a new statistical method making use of all higher moments than the mean shower depth distribution is developed – as there is large disagreement in between all EAS simulation models. There is also an uncertainty, just as large, for any particular model, given uncertainties in particle interaction parameters extrapolated to much higher energies from Large Hadron Collider (LHC) data. The TA hybrid FD/SD data is found to be statistically compatible with a pure proton composition, though not incompatible with a light mixed composition, for all models of EAS above E≥10^18.4 eV. There is also no statistically significant evidence of the composition getting heavier at the highest energies. The combined information of a proton-like light composition, and anisotropy evidence suggestive of energy dependent magnetic deflection of UHECR, should be useful for informing future source searches and models of intergalactic propagation through magnetic fields.
Ključne besede: cosmic rays, UHECR, composition, anisotropy
Objavljeno v RUNG: 24.04.2020; Ogledov: 2916; Prenosov: 0
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48. Variations in U concentrations and isotope signatures in two Canadian lakes impacted by U mining: A combination of anthropogenic and biogeochemical processesWei Wang, Duc Huy Dang, Breda Novotnik, Thai T. Phan, R. Douglas Evans, 2019, izvirni znanstveni članek Opis: Temporal and vertical variations in uranium (U) concentrations and U isotope (δ238U, ‰) signatures were
examined in sediment cores collected seven times over a one year period, from two lakes in Ontario, Canada,
which are contaminated with U by historical mining activities. Bow Lake is holomictic, experiencing seasonal
anoxia, while the sediments of meromictic Bentley Lake are permanently anoxic. Average annual peak concentrations
of U in Bow Lake subsurface sediments were approximately 300 μg L−1 and 600 μg g−1 in porewater
and bulk sediments, respectively. Similar ranges of concentrations (900 μg L−1 and 600 μg g−1, respectively)
were observed in Bentley Lake sediments. The exceedingly high levels of U observed in the porewaters of both
lakes, as well as the seasonal variability in U levels, challenge the traditional paradigm regarding U chemistry,
i.e., that reduced U(IV) should be insoluble under anoxic conditions.
The average annual δ238U ‰ values at the sediment-water interface of both lakes were similar (i.e.,
0.47 ± 0.09‰ and 0.50 ± 0.16‰, relative to IRMM-184). The deep sediments in both Bentley Lake and Bow
Lake record U isotope composition with a typical fractionation of 0.6‰ relative to the surface water, confirming
authigenic U accumulation, i.e., negligible contribution of particulate material from the tailings. Also, the δ238U
values in porewater have an average offset of ca. −0.1‰ relative to bulk sediments in anoxic zones and are
reversed in the oxic sediment layer.
Ključne besede: Uranium
Isotope composition
Uranium tailings
Biogeochemical cycling
Redox chemistry
Objavljeno v RUNG: 09.10.2019; Ogledov: 3096; Prenosov: 0
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49. Atmospheric chemistry and physics in the atmosphere of a developed megacity (London): An overview of the REPARTEE experiment and its conclusionsRoy M Harrison, Manuel DallOsto, David C S Beddows, Alistair J Thorpe, William J Bloss, James D Allan, Hugh Coe, James R Dorsey, Martin W Gallagher, Claire Martin, John Whitehead, Paul I Williams, Roderick L Jones, Justin M Langridge, A K Benton, Stephen M Ball, Ben Langford, C Nicholas Hewitt, Brian Davison, Damien Martin, K Fredrik Peterson, Stephen J Henshaw, Iain R. White, Dudley E Shallcross, Janet F Barlow, Tyrone Dunbar, Fay Davies, Eiko Nemitz, Gavin J Phillips, Carole Helfter, Chiara F Di Marco, Steven Smith, 2012, pregledni znanstveni članek Opis: The Regents Park and Tower Environmental Experiment (REPARTEE) comprised two campaigns in London in October 2006 and October/November 2007. The experiment design involved measurements at a heavily trafficked roadside site, two urban background sites and an elevated site at 160-190 m above ground on the BT Tower, supplemented in the second campaign by Doppler lidar measurements of atmospheric vertical structure. A wide range of measurements of airborne particle physical metrics and chemical composition were made as well as measurements of a considerable range of gas phase species and the fluxes of both particulate and gas phase substances. Significant findings include (a) demonstration of the evaporation of traffic-generated nanoparticles during both horizontal and vertical atmospheric transport; (b) generation of a large base of information on the fluxes of nanoparticles, accumulation mode particles and specific chemical components of the aerosol and a range of gas phase species, as well as the elucidation of key processes and comparison with emissions inventories; (c) quantification of vertical gradients in selected aerosol and trace gas species which has demonstrated the important role of regional transport in influencing concentrations of sulphate, nitrate and secondary organic compounds within the atmosphere of London; (d) generation of new data on the atmospheric structure and turbulence above London, including the estimation of mixed layer depths; (e) provision of new data on trace gas dispersion in the urban atmosphere through the release of purposeful tracers; (f) the determination of spatial differences in aerosol particle size distributions and their interpretation in terms of sources and physico-chemical transformations; (g) studies of the nocturnal oxidation of nitrogen oxides and of the diurnal behaviour of nitrate aerosol in the urban atmosphere, and (h) new information on the chemical composition and source apportionment of particulate matter size fractions in the atmosphere of London derived both from bulk chemical analysis and aerosol mass spectrometry with two instrument types.
Ključne besede: megacity, trace gas, urban atmosphere, atmospheric transport, chemical composition, aerosol
Objavljeno v RUNG: 18.07.2019; Ogledov: 3321; Prenosov: 0
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50. Tracer concentration profiles measured in central London as part of the REPARTEE campaignDamien Martin, K Fredrik Petersson, Iain R. White, Stephen H Henshaw, Graham Nickless, Amy Lovelock, Janet F Barlow, Tyrone Dunbar, Curtis R Wood, Dudley E. Shallcross, 2011, izvirni znanstveni članek Opis: There have been relatively few tracer experiments carried out that have looked at vertical plume spread in urban areas. In this paper we present results from two tracer (cyclic perfluorocarbon) experiments carried out in 2006 and 2007 in central London centred on the BT Tower as part of the REPARTEE (Regent's Park and Tower Environmental Experiment) campaign. The height of the tower gives a unique opportunity to study vertical dispersion profiles and transport times in central London. Vertical gradients are contrasted with the relevant Pasquill stability classes. Estimation of lateral advection and vertical mixing times are made and compared with previous measurements. Data are then compared with a simple operational dispersion model and contrasted with data taken in central London as part of the DAPPLE campaign. This correlates dosage with non-dimensionalised distance from source. Such analyses illustrate the feasibility of the use of these empirical correlations over these prescribed distances in central London.
Ključne besede: advection, concentration (composition), dispersion, tracer, urban atmosphere, vertical mixing, vertical profile
Objavljeno v RUNG: 18.07.2019; Ogledov: 3285; Prenosov: 0
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