Bulletin of the American Physical Society
APS April Meeting 2015
Volume 60, Number 4
Saturday–Tuesday, April 11–14, 2015; Baltimore, Maryland
Session Y9: Invited Session: New Results on Cosmic Rays |
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Sponsoring Units: DAP Chair: Angela Olinto, University of Chicago Room: Key 5 |
Tuesday, April 14, 2015 1:30PM - 2:06PM |
Y9.00001: Searching for Dark Matter with Cosmic Rays Invited Speaker: Eun-Suk Seo One of the most exciting possibilities in cosmic ray research is the potential to discover new phenomena. A number of elementary particles were discovered in cosmic rays before modern-day accelerators became available to study their detailed properties. Since the discovery of cosmic ray antiprotons in 1979 using a balloon-borne magnet spectrometer, a series of magnet spectrometers have been flown to search for the signature of dark matter annihilation in antiprotons and positrons. Being the same as particles except for their opposite charge sign, antiparticles are readily distinguished as they bend in opposite directions in the magnetic field. As long-duration balloon flights over Antarctica became available, not only antiproton to proton ratios but also measurements of antiproton energy spectra became possible. More recently, space missions are also providing precision measurements of electron and position energy spectra. With other measurements to constrain cosmic ray propagation models, these new measurements play key roles in constraining dark-matter models for understanding the nature of dark matter. Recent results, their implications, and outlook for the field will be presented. [Preview Abstract] |
Tuesday, April 14, 2015 2:06PM - 2:42PM |
Y9.00002: Direct and Indirect Detection of Cosmic Rays by HAWC Invited Speaker: Brenda Dingus The High Altitude Water Cherenkov (HAWC) observatory detects extensive air showers initiated by cosmic rays and gamma rays with energies from less than 100 GeV to greater than 100 TeV. More than one third of the HAWC array has been collecting data since August 2013 and the full array will be operational by March 2015. HAWC has detected an anisotropy in the arrival directions of the cosmic rays that has power on angular scales smaller than 10 degrees, which is difficult to explain given the propagation of these charged particles through the expected magnetic fields between the nearest sources and Earth. HAWC has also detected multiple Galactic gamma-ray sources, which are indirect probes of the sources of cosmic rays, because the cosmic rays interact in the sources to produce gamma rays, that unlike the charged cosmic rays, point back to their source. With future HAWC observations we will constrain the spectrum of these sources at the highest energies to look for signatures of gamma rays produced by interactions of hadronic cosmic rays. And HAWC has detected the extragalactic source, Mrk421. With longer exposures HAWC will likely detect more of these active galactic nuclei which may be the sources of the highest energy cosmic rays. We will search for indirect evidence of hadronic cosmic-ray acceleration in these sources as well, by studying their gamma-ray spectral and temporal signatures. [Preview Abstract] |
Tuesday, April 14, 2015 2:42PM - 3:18PM |
Y9.00003: Recent Results of the Telescope Array Experiment Invited Speaker: Dmitri Ivanov The Telescope Array (TA) is the largest cosmic ray experiment in the northern hemisphere and covers 10 PeV to 100 EeV range. TA is a hybrid detector that uses air fluorescence detectors combined with a ground array. TA consists of 507 plastic scintillation counters on a 1.2km square grid, overlooked by 3 fluorescence detector stations, and measures cosmic rays above 1 EeV. TA has collected 6.5 years of data. Results from the TA low energy extension (TALE), which sees cosmic rays down to 10 PeV, will also be shown. This contribution will consist of three parts. First, we will present the cosmic ray energy spectrum measured over 4 decades in energy. Next, we will discuss the latest results of the measurements of cosmic ray mass composition by the TA fluorescence detectors. Finally, we will show the latest results of the TA anisotropy measurements at the highest energies, where we have seen a concentration of events, called the ``hotspot,'' centered in the Ursa Major. [Preview Abstract] |
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