Department of Physics & Astronomy Colloquia

May 8, 2014 Dr. Yelena A. Prok, Old Dominion University

NUCLEON SPIN STRUCTURE: NEW RESULTS FROM JEFFERSON LAB

Host: Dr. Dipangkar Dutta

Abstract:

      Understanding the spin structure of the nucleon remains an open challenge of particle physics, nearly 30 years after the initial discovery of the ”spin crisis” by the European Muon Collaboration at CERN in 1980s. A vast set of polarization data has been accumulated over the next two decades at CERN, DESY and SLAC, with deep inelastic lepton-hadron scattering being a key tool in the investigation of the helicity structure of the nucleon. New data of unprecedented statistical precision and extensive kinematic coverage have become available more recently from the experiments conducted at Jefferson Lab. Together with the recent results from RHIC, COMPASS and HERMES, these new data allow us to constrain polarized parton distributions, test pQCD predictions in the valence region of high-x, and put limits on the gluon contribution to the nucleon spin. In this talk I will give a brief overview of the current knowledge of the nucleon spin structure, present most recent results from Jefferson Lab’s Hall B, and discuss the anticipated data from future experiments.

May 5, 2014 Dr. Lamiaa El Fassi, Old Dominion University

Measuring Antiquarks in the Proton

Host: Dr. Dipangkar Dutta

Abstract:

      One of the most challenging goals of modern nuclear physics is to understand proton structure in terms of quarks and gluons and their interaction via Quan-tum Chromodynamics (QCD). By scattering electrons and muons (leptons) from the proton at high energy (Deep Inelastic Scattering or DIS), we have learned a lot about quark distributions and their QCD interactions. We can learn even more about the proton through the Drell-Yan process, where we detect electronantielectron or muon-antimuon pairs emitted by proton- proton or pion-proton collisions. In these collisions, the lepton-antilepton pair is created by the annihilation of a quark in one proton with an antiquark in the other proton, allowing us to measure the antiquark distributions inside the proton. The E-906/SeaQuest experiment, the latest Fermilab Drell-Yan measurement, aims to measure the anti-quark distribution of the nucleon up to a quark-momentum fraction (Bjorken-x) of 0.45, higher than previously measured. In addition, by measuring proton-nucleus collisions, we can study quark energy loss in cold nuclear matter, the nuclear dependence of J/psi production, and the EMC e ect in the Drell-Yan process. In this talk I will introduce proton structure, highlight some topics of Drell-Yan physics, describe the E-906/SeaQuest experiment and discuss future prospects.

April 28, 2014 Dr. Alex J. Yuffa, US Army Research Laboratory

CONSEQUENCES OF CAUSALITY IN ELECTRODYNAMICS

Host: Dr. Anatoli Afanasjev

Abstract:

      Linear response laws and causality (the effect cannot precede the cause) are of fundamental importance in physics. In the context of classical electrodynamics, students often have a difficult time grasping these concepts because the physics is obscured by the intermingling of the time and frequency domains. We analyse the linear response laws and causality in the time and frequency domains with the aim of pedagogical clarity. We will show that it is easy to violate causality in the frequency domain by making a vanishing absorption approximation. Further, we will show that there can be subtle differences between Fourier transforming Maxwell equations and using a monochromatic source function. We discuss how these concepts can be obscured and offer some suggestions to improve the situation.

April 14, 2014 Dr. Ahmed Hamed, University of Mississippi

RHIC PHYSICS, WHY? AND HOW?

Host: Dr. Dipangkar Dutta

Abstract:

      World-wide efforts over the past half-century have produced a remarkably successful theoretical framework to describe the fundamental matter constituents and their interactions, known as the Standard Model (SM). The SM of particle physics predicts two phase transitions that are relevant for the evolution of the early universe. One is responsible for the spontaneous electroweak symmetry breaking, and the other is related to the spontaneous chiral symmetry breaking and confinement. The relativistic heavy ion collisions provide a unique opportunity to explore the second phase transition, which created 98 % of the visible mass of our universe. In this talk I will discuss the importance and the physics opportunities at the Relativistic Heavy Ion Collider (RHIC), and the experimental techniques. I will highlight few of the most important measurements at RHIC and LHC in the field of heavy ion collisions, and discuss the near future plans and detector upgrades.

April 3, 2014 Dr. Dustin Keller, University of Virginia

Electromagnetic Decays of the Low-Lying Excited-State Hyperons in the Strange Sector

Host: Dr. Dipangkar Dutta

Abstract:

      The branching Ratio of the electromagnetic (EM) decays of the lower mass strange baryons are investigated using the CEBAF Large Acceptance Spectrometer (CLAS) detector at Thomas Jefferson National Accelerator Facility. Hyperons produced through low-rate strangeness-conserving reactions can be used to measure EM transitions to other decuplet baryons. These small electromagnetic decay branching ratios are difficult to measure directly and extensions of the measuring techniques are developed. Ultimately these measurements are needed to understand the nature of the baryon wave-functions. The results from these electromagnetic decays allow for a Uspin symmetry test using the U-spin SU(3) multiplet representation. A new set of predictions of the unmeasured EM transition magnetic moments is also made.

Mar. 31, 2014 Dr. Vincent Sulkosky, Longwood University

Unveiling the Nucleus With Electrons

Host: Dr. Dipangkar Dutta

Abstract:

      Protons and neutrons, commonly referred to as nucleons, comprise the majority of the visible matter in the universe. We know that the nucleon is a composite particle, whose internal dynamics is governed by the strong nuclear force, which also binds protons and neutrons into a nucleus of an atom. Knowledge of the nucleon’s properties such as the nucleon’s electromagnetic charge and magnetization is crucial in our understanding of how the nucleon is constructed. Over the past two decades, the Thomas Jefferson National Accelerator Facility (Jefferson Lab) has become a leading institution for the study of the nucleon’s internal structure. Since the laboratory’s onset, several high precision measurements have been performed that have extended our knowledge of the nucleon and provided important tests of theoretical calculations. This study has grown rapidly with the development of highly polarized electron beams and targets. In this presentation, I will review the powerful tool of polarized electron scattering and highlight results from the Jefferson Lab program involving.

Mar. 27, 2014 Dr. Seamus Riordan, University of Massachusetts

Understanding the Strong Force Through Nucleon Structure

Host: Dr. Dipangkar Dutta

Abstract:

      Of the four fundamental forces in the universe, understanding the strong nuclear force represents a unique challenge due to the fact that it is the only strongly coupled theory that nature has presented and therefore difficult to perform calculations of its interactions from first principles. In its study, the nucleon has played a crucial role in formulating quantum chromodynamics and realizing the concepts of quarks and asymptotic freedom, in particular through the use of electroweak scattering probes. Nucleon elastic form factors, which contain information on the electric charge and magnetic moment distributions of the nucleons, and deep inelastic scattering processes, which contain information on the longitudinal momentum distribution of quarks, were some of the first measurements that were performed to access nucleon substructure and continue to be a rich source of new information. In this presentation, I will discuss how electron scattering has been and continues to be such a powerful experimental tool, as well as some recent results and future experiments involving elastic nucleon form factors at high momentumtransfer and parity-violating deep inelastic scattering.

Mar. 17, 2014 Dr. Kei Moriya, Indiana University

Hadron Spectroscopy and What We Can Learn About QCD from GlueX

Host: Dr. Dipangkar Dutta

Abstract:

      Quantum Chromodynamics, or QCD, is the force that binds quarks and gluons together to form bound states called hadrons. While QCD is universally accepted as the correct theory that describes the strong force, due to the strongly coupled nature there is no direct path connecting it and the plethora of bound states that are observed in experiments at the GeV scale. The upcoming GlueX Experiment at Jefferson Lab will explore the spectrum of hadrons and aims to expand our knowledge of hadron interactions and their connections with the underlying theory of QCD. This flagship experiment of the Jefferson Lab 12 GeV upgrade will use a photon beam to produce many bound states of interest, and the high beam intensity and large angular coverage of the detector will enable the collection of large samples of the multi-particle final states produced. In this talk I will discuss what we hope to learn about the spectrum of these states, and how this will further our understanding of how QCD works in this energy regime. Details of the experiment will be provided, and some possible analyses involving strangeness states will be discussed.

Feb. 24, 2015 Prof. Sanjoy K. Sarker, University of Alabama

QUANTUM LATTICE (GAUGE) ORDER CONNECTING HIGH-TC SUPERCONDUCTIVITY IN CUPRATES TO MOTT INSULATOR

Host: Dr. Jinwu Ye

Abstract:

      The physics of unusual metallic and superconducting phases in underdoped cuprates is often thought to be connected with that of the nearby Mott insulator. However, numerous attempts - mostly based on the t-J model - at establishing this connection and constructing a successful theory have run into serious bottlenecks, and failed. I will discuss how these bottlenecks are removed if one assumes that long-range antiferromagnetic order found in the insulator is destroyed by hole motion (as is the case in cuprates), thereby strongly renormalizing the theory. The resulting renormalized Hamiltonian, obtained from the parent model and valid for the underdoped region, has been analyzed by continuing the known spin phases from the insulator without changing their symmetry, thereby a) establishing the connection and b) constraining the theory completely. The phases are the same ones as found in cuprates, consistent with observed properties. Theory also explains why the metallic state is two dimensional in cuprates. I will discuss several predictions. An important one is the existence of a new quantum lattice (gauge) order unique to these systems, which characterizes the pseudogap and superconducting phases, but is absent in the strange metal phase.

Feb. 17, 2014 Prof. Marco Cavaglia, University of Mississippi

Coming Soon: Advanced LIGO

Host: Dr. Angelle Tanner

Abstract:

      In 1916 Albert Einstein demonstrated that the theory of general relativity allows for wave-like solutions. Although there is indirect proof of the existence of these waves, gravitational waves have not been directly observed yet. The Laser Interferometer Gravitational-wave Observatory (LIGO) is the world￠s leading scientific experiment for the detection of astrophysical gravitational waves. The LIGO detectors are currently undergoing a major upgrade. The new Advanced LIGO interferometers will soon be the world's largest precision optical instruments and the most sensitive gravitational wave detectors ever built. In this talk I will present an overview of the LIGO science, and challenges and prospects of experiments with Advanced LIGO detectors.

2013-2014 Committee