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Seminars for the week of
4/14/2014 - 4/18/2014

Atomic
Monday, April 14 Brian Richards [Host: Bob Jones]
3:30 PM, Room 204 University of Virginia
Physics Building “Using the Dipole-Dipole Force to Control Minimum Atom Separation”

Special HEP seminar
Tuesday, April 15
Note Special Day James D. Bjorken [Host: PQ Hung]
12:30 PM, Room 210
Note Special Time and/or Room SLAC
Physics Building “Darkness”

Nuclear
Tuesday, April 15 Dipak Rimal [Host: Xiaochao Zheng]
3:30 PM, Room 204 Florida International University
Physics Building “Proton Form Factor Puzzle and the CLAS Two-Photon Exchange Experiment”
ABSTRACT:

The electromagnetic form factors of the proton are extracted by analyzing unpolarized and polarized electron scattering data assuming the Born approximation. The extracted ratios of electric to magnetic form factors (GE/GM) by the two methods show a significant discrepancy that increases with Q2. One possible explanation for the observed discrepancy is the contribution from two-photon exchange (TPE) eff ects, which are not generally accounted for in the standard treatment of radiative corrections. Theoretical calculations estimating the magnitude of the TPE effect are highly model-dependent and limited experimental evidence for such e ffect exists. The ratio of positron-proton to electron-proton elastic scattering cross sections (R = σ(e+ p)/σ(e- p)) provides a model-independent measurement of the TPE e ffect. One such measurement of R was performed by using a mixed electron-positron beam at Jeff erson Lab Hall B. Both electrons and positrons were elastically scattered from a 30-cm-long liquid hydrogen target. The resulting scattered particles were detected in CLAS. The elastic events were then identified by using elastic scattering kinematics. The measurement covers a range of Q2 < 2 GeV2 and 0:1 < ε < 1. In the kinematics of the experiment, our results are consistent with the hadronic calculation of the TPE e ffect by Blunden, Melnitchouk, and Tjon. The details of the CLAS TPE experiment and the results will be discussed.

High Energy
Wednesday, April 16 KC Kong [Host: Craig Group]
3:30 PM, Room 204 University of Kansas
Physics Building “Extra Dimensions: Where Do We Stand?”

Condensed Matter
Thursday, April 17 Stephen Wilson [Host: Seunghun Lee]
3:30 PM, Room 204 Boston College
Physics Building “Looking beyond the spin-orbit Mott phase”
ABSTRACT:

An unusual manifestation of Mott physics dependent on strong spin-orbit interactions has recently been identified in a growing number of classes of 5d transition metal oxides built from Ir4+ ions. Instead of the naively expected increased itinerancy of these iridates due to the larger orbital extent of their 5d valence electrons, the interplay between the amplified relativistic spin-orbit interaction (intrinsic to large Z iridium cations) and their residual on-site Coulomb interaction U, conspires to stabilize a novel class of spin-orbit assisted Mott insulators with a proposed Jeff=1/2 ground state wavefunction. The identification of this novel spin-orbit Mott state has been the focus of recent interest due to its potential of hosting a variety of new phases driven by correlated electron phenomena (such as high temperature superconductivity or enhanced ferroic behavior) in a strongly spin-orbit coupled setting. Currently, however, there remains very little understanding of how spin-orbit Mott phases respond to carrier doping and, more specifically, how relevant U remains for the charge carriers of a spin-orbit Mott phase once the bandwidth is increased. Here I will present our group’s recent experimental work exploring carrier doping and the resulting electronic phase behavior in one such spin-orbit driven Mott material, Sr3Ir2O7, with the ultimate goal of determining the relevance of U and electron correlation effects within the doped system’s ground state. Our results reveal the stabilization of an electronically phase separated ground state in B-site doped Sr3Ir2O7, suggestive of an extended regime of localization of in-plane doped carriers within the spin-orbit Mott phase. This results in a percolative metal-to-insulator transition with a novel, global, antiferromagnetic order. The electronic response of B-site doping in Sr3Ir2O7 will then be compared with recent results exploring A-site doping of electrons into the system and the resulting electronic phase diagrams discussed.

INPP Second Annual Lecture
Friday, April 18 Gordon Kane [Host: Dinko Pocanic]
3:30 PM, Room 203
Note Special Time and/or Room University of Michigan
Physics Building “String Theory, Our Real World, and Higgs bosons”
ABSTRACT:

String theory is exciting because it can address most or all of the questions we hope to understand about the physical world, about the quarks and leptons that make up our world, and the forces that act on quarks and electrons to form our world, cosmology, and much more. It’s nice that it provides a quantum theory of gravity too. I’ll explain why string theory is testable in basically the same ways as the rest of physics, why many people including string theorists are confused about that, and how string theory is already or soon being tested in several ways, including Higgs boson physics and LHC physics.

INPP Second Annual Lecture
Friday, April 18
Note Special Day Gordon Kane [Host: Dinko Pocanic]
3:30 PM, Room 204 University of Michigan
Physics Building “String Theory, Our Real World, and Higgs bosons”
ABSTRACT:

String theory is exciting because it can address most or all of the questions we hope to understand about the physical world, about the quarks and leptons that make up our world, and the forces that act on quarks and electrons to form our world, cosmology, and much more. It’s nice that it provides a quantum theory of gravity too. I’ll explain why string theory is testable in basically the same ways as the rest of physics, why many people including string theorists are confused about that, and how string theory is already or soon being tested in several ways, including Higgs boson physics and LHC physics.

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