Bulletin of the American Physical Society
APS April Meeting 2020
Volume 65, Number 2
Saturday–Tuesday, April 18–21, 2020; Washington D.C.
Session D09: Ultra High-energy Cosmic Ray ObservationsLive
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Sponsoring Units: DAP Chair: Foteini Oikonomou, Technische Universität München (TUM) / ESO Room: Roosevelt 4 |
Saturday, April 18, 2020 3:30PM - 3:42PM Live |
D09.00001: The Cosmic Ray Spectrum Meausred at the Pierre Auger Observatory Alan Coleman The Pierre Auger Observatory is the world's largest cosmic ray detector and has been taking data for over 16 years. In this time, an unprecedented amount of statistics has been collected which allows for high precision measurements of the most energetic particles ever observed. In this presentation, the measurement of the all-particle cosmic ray spectrum will be shown as measured by both the surface detector (SD) and fluorescence detector (FD). Auger’s two nested SD arrays consist of hexagonal arrays of water Cherenkov detectors with 1500m and 750m spacing. The FD consists of four sets of six telescopes that overlook the SD, calorimetrically measures the electromagnetic content of >100 PeV air showers, and sets the energy scale for the observatory. This presentation will include five distinct measurements of the all particle spectrum, three from the SD and two from the FD, covering primary energies 16.5 $\leq$ lg(E/eV) $\leq$ 20.5. Additionally, a combined spectrum using these observations will be shown with a combined exposure of 80,000 km$^2$ sr yr. The combined spectrum spans more than four order of magnitude in energy and clearly displays two distinct inflection points in the spectrum (the so-called “second knee” and “ankle”) as well as a suppression at the highest energies. [Preview Abstract] |
Saturday, April 18, 2020 3:42PM - 3:54PM Live |
D09.00002: Recent Anisotropy Results from the Pierre Auger Observatory John Farmer The Pierre Auger Observatory, located in Mendoza, Argentina, is the world's largest Ultra-High Energy Cosmic Ray (UHECR) observatory and has accumulated an unprecedented exposure to UHECRs (over 100,000 km$^2$ sr yr) throughout more than fifteen years of operation. In this contribution, we report on the results from recent searches for anisotropies in the arrival directions of UHECRs. We present the observation of a large-scale dipole in arrival directions and the evolution of its phase and amplitude over more than three decades of energy. We also discuss the results from several anisotropy studies at small and intermediate scales, including correlations with candidate sources and model-independent local overdensity searches. [Preview Abstract] |
Saturday, April 18, 2020 3:54PM - 4:06PM Live |
D09.00003: AugerPrime: the Upgrade of the Pierre Auger Observatory Frederic Sarazin The nature and origin of ultra-high energy cosmic-rays (UHECRs) remain largely a mystery despite a wealth of new information obtained in recent years at the Pierre Auger Observatory (Auger) and elsewhere. In order to answer those open questions, the Auger collaboration has embarked in an upgrade of the Observatory (``AugerPrime''). It will employ a combination of new scintillator and radio detectors to make the surface detector more sensitive to primary composition, a key to unlock the UHECR conundrum. In this presentation, the science case for the upgrade, its technical realization and initial results from the AugerPrime engineering array will be discussed. [Preview Abstract] |
Saturday, April 18, 2020 4:06PM - 4:18PM Live |
D09.00004: Status of the Auger – Telescope Array surface detector cross-calibration effort (Auger@TA) Jeff Johnsen Auger@TA is a joint experimental program of the Telescope Array (TA) and the Pierre Auger Observatory (Auger), the two leading Ultra-High Energy Cosmic-Ray (UHECR) experiments located respectively in the northern and southern hemispheres. The aim of the program is to achieve a cross-calibration of the Surface Detector (SD) from both experiments. Auger and TA SD stations are based on different detection media and respond differently to the electromagnetic and muonic components of UHECR showers. In this presentation, we discuss the results of the first phase of the effort, a comparative response study of a pair of co-located Auger and TA SD stations deployed within TA. We will also discuss our plan for the second phase, which consists of the deployment of an independently-operated Auger hexagon (7 stations) inside TA to perform event-level comparisons. [Preview Abstract] |
Saturday, April 18, 2020 4:18PM - 4:30PM Live |
D09.00005: Cosmic Ray Composition and Energy Spectrum from PeV to EeV using IceCube and IceTop Matthias Plum, Karen Andeen The IceCube Neutrino Observatory at the South Pole is a multi-component detector capable of measuring the cosmic ray energy spectrum and composition from PeV to EeV, the energy region typically thought to cover the transition from galactic to extragalactic sources of cosmic rays. The IceTop array at the surface is sensitive to the electromagnetic part of the air shower while the deep in-ice array detects the high-energy (TeV) muonic component of air showers. IceTop's reconstructed shower size parameter, $S_{125}$, is unfolded into a high statistics all-particle energy spectrum. Furthermore, for air showers that pass through both arrays, the in-ice reconstructed muon energy loss information is combined with $S_{125}$ in a machine learning algorithm to simultaneously extract both the all-particle energy spectrum and individual spectra for elemental groups. The all-particle spectra as well as spectra for individual elemental groups will be presented, as well as plans for future analyses. [Preview Abstract] |
Saturday, April 18, 2020 4:30PM - 4:42PM |
D09.00006: Telescope Array Experiment Dmitri Ivanov Cosmic rays of energies 10$^{\mathrm{15}}$ to 10$^{\mathrm{20}}$ eV and beyond are believed to be charged nuclei of galactic and extragalactic origins that are accelerated by violent events in the Universe and which propagate through the galactic and extragalactic fields and photon backgrounds before they finally reach the Earth, where they can be observed using very large cosmic ray detectors. To understand cosmic ray origin and propagation mechanisms, physicists study cosmic ray energy spectrum, mass composition, and anisotropies of their arrival directions. In this presentation, we report on the recent progress of these measurements by the Telescope Array Experiment, the largest cosmic ray detector in the Northern hemisphere, that was built in Utah, which consists of large ground arrays of plastic scintillator counters overlooked by the fluorescence detectors. [Preview Abstract] |
Saturday, April 18, 2020 4:42PM - 4:54PM |
D09.00007: Telescope Array 10 year Composition William Hanlon Estimates of the composition of ultra high energy cosmic rays (UHECRs) can be inferred by recording the depth of air shower maximum, $X_{\mathrm{max}}$, for many showers and comparing the distributions to those predicted by Monte Carlo simulations. Telescope Array is designed to answer the question of what elements are present in the UHECR spectrum, which is still unknown. Composition is a strong constraint on models which describe the sources and propagation of UHECRs. In this talk we present the most recent results of nearly 10 years of Telescope Array hybrid $X_{\mathrm{max}}$ measurements which is found to agree with a predominantly light composition through comparison of the means and standard deviations of the $X_{\mathrm{max}}$ distributions. We further this analysis by presenting the first measurement of TA composition built upon an ad hoc four component model of protons, helium, nitrogen, and iron. Through a profile likelihood analysis we measure the distribution of fractions of the four elements that best agree with TA data and observe a predominantly light composition consisting of proton and helium between $10^{18.2} - 10^{19.1}$ eV, with small contribution from nitrogen and iron, which does not change with energy. [Preview Abstract] |
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