William & Mary

Spring 2016

January 21, 2016 (Thursday) 4:00-5:00p.m. Small Hall 111
Speaker: Prof. Jozef Dudek , Jefferson Lab & Old Dominion University
Host: Prof. K. Orginos
Title: The elusive excited glue of QCD
Abstract: Quarks and gluons are believed to be the building blocks of hadrons, the strongly interacting particles of nuclear physics. Making predictions regarding the spectrum of hadrons within Quantum Chromodynamics (QCD), the field theory that describes quarks and gluons, has long been challenging. One particular mystery within QCD is whether the role of excitations of the gluon field, which is strongly coupled to both itself and to the quarks, can be observed in the excited spectrum of hadrons.  
I will present results from numerical calculations of QCD that indicate that exotic objects called hybrid hadrons, in which quarks are partnered with an excitation of the gluon field, are in fact a feature of the hadron spectrum and should be experimentally observable. Recent theoretical advances have allowed production and decay properties of excited hadrons to be calculated, opening up the possibility of providing predictions that offer guidance for current and near-future experimental exotic hadron searches.

January 28, 2016 (Thursday) 4:00-5:00p.m. Small Hall 111
Speaker: Dr. Christoher Monahan, Rutgers University
Title: One quark, two quarks, three: How to build a proton with lattice QCD
Abstract: Protons and neutrons make up most of the mass of the visible Universe, but our knowledge of their internal structure is far from complete. Quantum chromodyamics (QCD), the theory of the strong force, provides the mathematical framework that connects protons and neutrons to their constituent quarks and gluons, but QCD cannot be solved analytically. 
Instead, we must use lattice QCD, in which we discretise spacetime and study QCD numerically, usually on large supercomputers. I will introduce lattice QCD, discuss our need for a numerical approach to QCD, and highlight some of the many ways in which lattice QCD contributes to our understanding of particle and nuclear physics.

February 4, 2016 (Thursday) 4:00-5:00p.m. Small Hall 111
Speaker: Dr. Phiala Shanahan
Title: The strange proton: Why strange quarks are important in nucleon structure
Abstract: Protons and neutrons are the fundamental building blocks of atomic nuclei and constitute more than 99% of the visible mass in the universe. While understanding proton properties is clearly of fundamental importance, there are still many open questions. For example, the size of the proton has become a topic for debate as different experimental approaches give inconsistent values for its charge radius by 5 standard deviations. On the theory front, the modern picture of the proton is of a complex particle with a substructure of more basic constituents named quarks and gluons. Many proton properties are well-described within a model where only two ‘flavors' of quark appear: the up and down quarks. However, the theory of the strong interaction, Quantum Chromodynamics (QCD), describes a much more complicated dynamical structure in which quark-antiquark pairs of any flavor, such as strange quarks, can contribute. In this colloquium I will show why a quantitative understanding of the role of strange quarks in the proton is important in the context of physics issues as diverse as the experimental detection of dark matter particles, precision tests of the Standard Model, and the proton radius puzzle. I will describe how recent advances in numerical simulations of QCD have led to new benchmarks for experiments and new levels of precision in dark matter searches. 

February 11, 2016 (Thursday) 4:00-5:00p.m. Small Hall 111
Speaker: Dr. Maxwell Hansen, (Institut für Kernphysik Johannes Gutenberg-Universität Mainz) Host: K. Orginos
Title:  From effective theories to quantum fields on the lattice: big ideas for femtoscale physics
Abstract: 
One of the most important ideas in physics is that of effective theories. This is based on the simple observation that different tools are required to describe systems of vastly different sizes. Starting here, I will introduce the Standard Model as the most effective known description of the smallest lengths we can measure. I will then turn attention to quantum chromodynamics (QCD), the part of the Standard Model that describes the strong force, responsible for protons, neutrons and the nuclei they form. QCD has a fascinating, rich structure that has proven highly challenging for theorists to understand. I will give motivation for using a space-time lattice to study QCD and will give various examples to illustrate the method, with particular focus on scattering predictions. 

February 12, 2016 (Friday) 4:00-5:00p.m. Small Hall 111
Speaker: Dr. Seamus Riordan, Stony Brook University
Host: P. Vahle
Title: Studying the Dark Side of the Nucleus:  From Neutron Skins to Neutron Stars
Abstract: The neutron densities in atomic nuclei are notoriously difficult to observe with high precision:  the standard tool of electromagnetic interactions which has been used to map out the nuclear charge distributions simply doesn't see them.  In fact, it has only recently been experimentally confirmed that the neutron-rich lead nucleus even has a neutron skin, and is only a fraction of a neutron radius thick.   Encoded in these distributions is a wealth of important information about how the strong nuclear force builds systems where the number of protons and neutrons are unequal.  This information has bearing not only for our understanding of asymmetric nuclei, but also in the construction of extreme systems like neutron stars.  Fortunately, nature gives us a novel way to image this side of the nucleus: through fundamental weak force interactions, which interact primarily to neutrons rather than protons. In this colloquium I will discuss why these neutron distributions play an important part in our understanding of nuclear physics and astrophysics, how one images such tiny systems with electron beams, and the recent and upcoming experimental efforts for such measurements.

February 18, 2016 (Thursday) 4:00-5:00p.m. Small Hall 111
Speaker: Dr. Matha Constantinou
Host: K. Orginos
Title: 
Simulating The Visible World
Abstract: Quantum Chromodynamics (QCD) is the theory of the strong interactions that binds quarks and gluons to form the nucleons, the fundamental constituents of visible matter.

Understanding the structure of the nucleon from first principles is a milestone of hadron physics and numerous experiments have been devoted to its study. Lattice QCD is a powerful approach for the ab initio calculation of the properties of hadrons and their interactions. 
Over the last five years, lattice QCD has made significant progress yielding results that can be compared to experimental measurements with controlled systematics.
We will review recent progress of lattice QCD results with emphasis on nucleon structure and, in particular, addressing questions, such as: “What is the size of a proton" and “What contributes to the spin of proton”? The quark content of the nucleon is also discussed, as an important quantity related to the explicit chiral symmetry breaking in QCD, as well as, entering the interpretation of experimental searches for dark matter.


February 24, 2016 (Wednesday) 4:00-5:00p.m. Small Hall 111
Speaker: Dr. Simona Malace
Host: P. Vahle
Title: 
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February 26, 2016 (Friday) 4:00-5:00p.m. Small Hall 111
Speaker: Dr. Paul Mattione
Host: K. Griffioen
Title: 
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March 2, 2016 (Wednesday) 4:00-5:00p.m. Small Hall 111
Speaker: Dr. Justin Stevens
Host: W. Deconinck
Title: 
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March 3, 2016 (Thursday) 4:00-5:00p.m. Small Hall 111
Speaker: Dr. Gernot Eichmann
Host: K. Orginos
Title: 
From quarks and gluons to the structure of hadrons
Abstract: Quarks and gluons are the fundamental building blocks of visible matter, yet we cannot observe them because they are confined inside hadrons. In light of ongoing experimental advances, the theoretical description of hadrons within Quantum Chromodynamics (QCD) still poses an enormous challenge. To name a few questions: what is the nature of baryon resonances? Do tetraquarks and pentaquarks exist and if yes, how should we interpret them? Can we describe nucleon form factors, polarizabilities, or electroproduction amplitudes from the level of quarks and gluons, and how is such a description related to effective field theories? What is the QCD contribution to the anomalous magnetic moment of the muon? And is it possible to understand nuclei from the fundamental interactions in QCD?
 

Here I will present an approach employing Dyson-Schwinger, Bethe-Salpeter and Faddeev equations, whose basic promise is to calculate hadron properties from the nonperturbative structure of the underlying Green functions in QCD – the quark and gluon propagators, quark-gluon vertex etc. I will discuss the basic ideas and highlight some recent progress that has been made regarding the spectrum of mesons and baryons, tetraquarks, nucleon and nucleon resonance form factors, Compton scattering, and the muon g-2 problem.


March 4, 2016 (Friday) 4:00-5:00p.m. Small Hall 111
Speaker: Dr. Anselm Vossen
Host: W. Deconinck
Title: 
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March 14, 2016 (Monday) 4:00-5:00p.m. Small Hall 111
Speaker:
Dr. David Abergel
Host:
E. Rossi
Title: 
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April 1, 2016 (Friday) 4:00-5:00p.m. Small Hall 111
Speaker:
Prof. Charles Perdrisat
Host: E. Tracy
Title: 
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April 8, 2016 (Friday) 4:00-5:00p.m. Small Hall 111
Speaker: Will Wester
Host: 
M. Kordosky
Title: 
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April 15, 2016 (Friday) 4:00-5:00p.m. Small Hall 111
Speaker:
Prof. Sankar Das Sarma (University of Maryland)
Host: E. Rossi
Title: 
Quantum Many Body Localization
Abstract: How does an isolated quantum system come to thermal equilibrium due to interaction between its constituent subsystems?  Or does it?  What underlies the condition for quantum ‘ergodicity’?  These are some of the basic questions to be discussed in this talk.  The topic is of fundamental importance since it deals with the applicability of thermodynamics and statistical mechanics to isolated quantum systems, and asks the extent to which an isolated (macroscopic) quantum system can be considered to be acting as its own heat bath.
April 22, 2016 (Friday) 4:00-5:00p.m. Small Hall 111
Speaker:
Prof. Utpal Chatterjee (UVA)
Host: E. Rossi
Title: 
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