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Events on Thursday, March 5th, 2015

Astronomy Colloquium
"News from the Extreme Energy Cliff"
Time: 3:30 pm
Place: 4421 Sterling Hall
Speaker: Professor Angela Olinto, University of Chicago
Abstract: Thanks to giant extensive air-showers observatories, such as the Pierre Auger Observatory and the Telescope Array (TA), we now know that the sources of ultrahigh energy cosmic rays (UHECRs) are extragalactic. We also know that either they interact with the CMB as predicted or they run out of energy at the same energy scale of the CMB interactions! Their composition is either surprising (dominated by heavier nuclei at the highest energies) or the hadronic interactions at 100 TeV are not a standard extrapolation of LHC interaction energies. Hints of anisotropies begin to appear as energies reach 60 EeV, just when statistics become very limited.
Basic questions remain unanswered: What generates such extremely energetic particles that reach above 10^20 eV (100 EeV)? Where do they come from? How do they reach these energies? What are they? How do they interact on their way to Earth and with the Earth’s atmosphere?
A hotspot seen by TA may be the first hint of a source. Neutrino and gamma-ray follow ups may clarify this tantalizing possibility. In addition, a large increase in statistics of UHECRs is needed. Space missions are now being studied to increase the exposure to UHECR such as the JEM-EUSO mission: the Extreme Universe Space Observatory (EUSO) at the Japanese Experiment Module (JEM).
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