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Events on Friday, February 25th, 2011

Special High Energy Physics Seminar
First Results of Higgs Searches and Prospects for 2011/2012 with the ATLAS Detector at the LHC
Time: 2:30 pm - 3:45 pm
Place: 5280 Chamberlin Hall
Speaker: Bruce Mellado, UW-Madison Physics Department
Abstract: The Higgs boson is responsible for giving masses to particles. The first results of Higgs searches using data taken in 2010 with the ATLAS detector at the LHC are reported. The sensitivity of Higgs searches with masses in the range 140&amp;amp;lt;M_H&amp;amp;lt;190 GeV is dominated by the decay H-&amp;amp;gt;WW. The details of the search with this channel and the extraction of Standard Model backgrounds are reviewed. Results are compared with those of the Tevatron. The prospects for the Higgs boson discovery in 2011/2012 are also reviewed.
Host: Matthew Herndon
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Physics Department Colloquium
Led by the Nodes: Forging an Understanding of Fe-Based Superconductors
Time: 4:00 pm
Place: 2241 Chamberlin Hall (coffee at 3:30 pm)
Speaker: Peter Hirschfeld, University of Florida
Abstract: The new Fe-based superconductors have occasioned considerable excitement because transition temperatures are high, and it is hoped that comparisons to cuprates will lead to new insights into the essential ingredients for high temperature superconductivity. I will briefly review some similarities and differences to the cuprates, focussing first on normal state magnetic and transport properties. In this respect some of the remarkable properties of these systems can be understood by consideration of the multiorbital character of the multisheeted Fermi surface. Next, I will review what is known about the superconducting state, explaining the basis for the near-consensus that all pnictide materials display spin singlet, orbital s-wave symmetry. Somewhat more controversial are differing reports on gap structure suggested by different experimental probes on different materials, including varying claims of gap nodes or fully gapped behavior. I will argue that such a diversity of gap structures, unexpected based on cuprate intuition, is characteristic of systems with s-symmetry and the unusual band structure of the Fe-based superconductors. They should, and do, display an "intrinsic sensitivity" to small perturbations of electronic structure. I review what is to be expected in this regard from spin fluctuation theories, where multiorbital effects are found again to play a crucial role. Finally, I will discuss how 3-dimensionality influences superconducting order.
Host: Chubokov
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