Fall 2012

Tuesday August 28, 2012

"The elusive excited glue of Quantum Chromodynamics"

Dr. Jo Dudek
Department of Physics
Old Dominion University

I will motivate the quark picture of hadron spectroscopy and show how it leads to the modern theory of the strong nuclear force, Quantum Chromodynamics, in which quarks are strongly coupled to the force-carriers, gluons. A strongly coupled gluonic field should have an excitation spectrum of its own - one which does not appear to be present in the experimental hadron spectrum. I will show how recent computations in lattice QCD performed by the speaker and his collaborators suggest that hadrons featuring gluonic excitations are indeed a feature of QCD and should exist at experimentally accessible energies. The impact of ongoing calculations of couplings to photons and decay rates relevant to searches at experimental facilities like GlueX and CLAS12 at Jefferson Lab will be discussed.

Tuesday September 4, 2012

"Atom Trap, Krypton-81, and Global Groundwater"

Dr. Zheng-Tian Lu
Argonne National Laboratory

The long-lived noble-gas isotope 81Kr is the ideal tracer for old water and ice in the age range of 10^5 - 10^6 years, a range beyond the reach of 14C. 81Kr-dating, a concept pursued over the past four decades by numerous laboratories employing a variety of techniques, is now available for the first time to the geoscience community at large. This is made possible by the development of an atom counter based on the Atom Trap Trace Analysis (ATTA) method, in which individual atoms of the desired isotope are selectively captured and detected with a laser-based atom trap. ATTA possesses superior selectivity, and is thus far used to analyze the environmental radioactive isotopes 81Kr, 85Kr, and 39Ar, These three isotopes have extremely low isotopic abundances in the range of 10^-16 to 10^-11, and cover a wide range of ages and applications. In collaboration with geoscientists, we are dating groundwater and mapping its flow in major aquifers around the world.

This work is supported by DOE, Office of Nuclear Physics, under contract DE-AC02-06CH11357; and by NSF, Division of Earth Sciences, under award EAR-0651161.

Tuesday September 18, 2012

"Cardiac Arrhythmias and the Geodesic Principle for Filaments in Excitable Media"

Dr. Christian Zemlin

Old Dominion University

In the Cardiac Electrophysiology Lab we study the mechanisms of arrhythmias both experimentally and from a theoretical point of view. Arrhythmias are disturbances in the normal electrical activity of the heart. In experiments, we extract animal hearts visualize their electrical activity using voltage-sensitive fluorescent probes. The most dangerous arrhythmias are reentrant arrhythmias; they are composed of self-sustained, high-frequency waves called "scroll waves" that rotate around one-dimensional phase singularities called filaments. Scroll waves exist not only in the heart but in a large variety of excitable media. The complex dynamics of scroll waves can be most efficiently described by via the dynamics of their filaments. Particularly elegant is the "geodesic principle" that allows the computation of steady state filaments for a large class of excitable media.

Tuesday September 25, 2012

"Higgs boson"

Dr. Marc Sher

William & Mary

The Standard Model of particle physics describes the strong, weak and electromagnetic interactions of all known fundamental particles with high precision. There remains, however, a crucial question: how do fundamental particles acquire their masses, since the symmetries of the Standard Model forbid them? The preferred explanation requires the existence of an additional particle, the Higgs boson. Discovery of the Higgs boson has been the major goal of experimental high energy physics for decades, and discovery of a Higgs boson at a mass of 125 GeV was announced at the LHC this summer. In this talk, I will introduce the Standard Model and discuss the importance of the Higgs and describe its properties. I will then talk about how it is detected, discuss the search for it over the past 25 years, and then describe the recent experimental results from the LHC and talk about expectations over the next few months and the implications for the future of elementary particle physics.

Tuesday October 16, 2012

"Energy Spread Reduction of Electron Beams Produced From Laser Wakefield Acceleration"

Dr. Bradley Pollock

Lawrence Livermore National Laboratory

Conventional RF linear accelerators produce high energy electron beams (10's of GeV) over kilometer-scale distances, where the long length is due to the maximum electric field these devices can generate without damaging the accelerator (10's MeV/m). The Laser Wakefield Acceleration mechanism provides a platform for producing high energy electron beams over centimeter-scale distances by creating an accelerating structure in a plasma capable of supporting ~GeV/cm electric fields. Here a short-pulse laser drives a relativistic plasma wave in an underdense plasma which in turn accelerates electrons. We have developed a novel multi-stage accelerator which allows for narrow energy spread electron beams to be produced at low electron densities, which are required to achieve high energy electrons from this technique. Experiments performed using the 60 fs, 200 TW Callisto laser at Lawrence Livermore National Laboratory's Jupiter Laser Facility have demonstrated ~0.5 GeV electron beam production with 5% energy spread over 8 mm; future experiments will seek to increase the energy gain to >2 GeV in 2 cm, while reducing the energy spread to

Tuesday November 13, 2012

"Synchrotron Radiation Sources and Free-Electron Laser - Research Tools of Extraordinary Versatility"

Dr. John Galayda

SLAC National Accelerator Laboratory

Synchrotron radiation is a key consideration in the design of electron or positron accelerators. As a tool for probing and imaging matter on the scales from Angstroms to centimeters, it has become an indispensable tool for many thousands of physicists, chemists, biologists and geologists. It has proven to be a powerful specialized tool for archaeologists and art historians as well. Free-electron lasers are specialized sources of synchrotron radiation that create and exploit the collective motion of electrons in accelerators to produce extremely short burst s of light so intense as to be usable for freeze-frame photography of atoms and molecules under static conditions and amidst dynamic processes such as the breaking of chemical bonds.

I will attempt to give a brief description of the properties of synchrotron radiation and some examples of experimental techniques they enable. I will describe basic characteristics of accelerators optimized as light sources and free-electron lasers. I will also give an overview of light sources and free-electron lasers operating now and in planning or construction worldwide

Tuesday November 20, 2012

"Angular scattering and holographic imaging microscopy as emerging techniques to characterize oceanic particles"

Dr. Michael Twardowski

WetLabs

Inversions have been developed to interpret unpolarized and polarized light scattering for undisturbed complex natural oceanic particle populations in terms of the particle subfractions (including bubbles) responsible for the scattering. The inversions are able to quantitatively solve for subfraction size distributions, refractive index (closely linked to particle density), and particle coating thickness where applicable. We have also developed an in-situ holographic microscope to characterize undisturbed particle size distributions, shapes, and orientations for particles as small as

Tuesday November 27, 2012

"Photoproduction of e+e- pairs at JLAB"

Dr. Stepan Stepanyan

Jefferson Lab

A broad program for studying the quark and gluon structure of hadrons, and in particular, probing nucleon structure using deeply virtual exclusive reactions (DVER) and the formalism of Generalized Parton Distributions (GPDs) is underway at Jefferson Lab. Deeply Virtual Compton Scattering (DVCS), ep â†' epγ, has been the focus of interest as it provides the cleanest tool for accessing the quark GPDs of the nucleon. Time-like DVCS, also known as Time-like Compton Scattering (TCS), is the inverse process to space- like DVCS that can be probed through the photo- production of lepton pairs (γp â†' γâˆ-p â†' l+lâˆ'p). Combining space-like and time-like data thus offers additional constraints on the GPDs. These studies will allow to gain fundamental insight into the nature of the Compton process in the partonic regime, to test the universality of GPDs by comparing spacelike and timelike DVCS (TCS), and to take advantage of the straightforward access in TCS to the real part of the Compton form factors. No prior TCS measurements exist except for pilot analyses of CLAS 6 GeV data, which demonstrated the general feasibility. With 11 GeV beam di-lepton invariant masses of up to 3.4 GeV can be reached. This will allow, in addition to quark GPDs, to access the nucleon’s gluonic structure at large x through J/Ψ photoproduction.

Tuesday December 4, 2012

"Senior Thesis Presentations"

Undergraduate Physics Major
Old Dominion University

"A MOTley Project: Building a Laser Lock, a Glass Cell, and a Vacuum Chamber for

Obtaining a Rubidium Magneto-Optical Trap (MOT)"

Dawn Hedges

"Remote Sensing Using a Continuous-wave Laser"

Eric Ingram