|January 16||UT: No Classes||NA|
|Cosmic ray flux measurements at global scale and the associated applications|
|Hard probes of the hot medium|
|February 13||Elena Bruna
|Open heavy-flavour physics|
|February 14 (Please Note Special Date/Place/Time: Room 307 at 11 AM)||Mustafa Rajabali
Tennessee Tech University
|Studying the structure of neutron-rich deformed nuclei via beta-decay|
|February 16 (Please Note Special Date/Place/Time: Room 307 at 11 AM)||Daniel Ayangeakaa
|Shape coexistence and the role of reflection and axial asymmetry in nuclei|
|February 20||Miguel Magdurga
|The birth of elements through nuclear decay in stellar furnaces|
|February 27||Calem Hoffman
Argonne National Laboratory
|Weak-binding effects in atomic nuclei|
|March 6||David Perez Loureiro
|Nuclear physics and astrophysics using decay of proton-rich nuclides|
|March 13||UT: No Classes||NA|
|March 20||Gautam Rupak
Mississippi State University
|Low-energy nuclear reactions using EFT|
|March 27||Yuri Efremenko
|CANCELLED: COHERENT experiment at the SNS|
|April 3||Jamie Coble
UTK Nuclear Engineering
|Advanced control for future nuclear reactors|
|April 10||Matthias Schindler
|Symmetry-violating nucleon-nucleon interactions in effective field theories|
|April 17||Cory Thornsberry
|Studying proton transfer reactions using the VANDLE neutron detector array|
|April 24||Gregory Potel||Inclusive deuteron-induced reactions|
Georgia State University
Cosmic ray flux measurements at global scale and the associated applications
Cosmic ray radiation has galactic origin and consists primarily of protons and a small percentage of heavier nuclei. The primary cosmic ray particles interact with the molecules in the atmosphere and produce showers of secondary particles at about 15 km altitude. In recent years, with the advancement of particle detection technology and massive computing power, there is a growing interest of exploring the applications of cosmic rays ranging from muon tomography, space and earth weather monitoring, etc. In this talk, I will present the recent work at Georgia State University on cosmic ray shower simulation, the development of low-cost cosmic ray detectors, and the plan for building a network of cosmic ray detectors around the globe.
University of Tennessee
Hard probes of the hot medium
The Pb--Pb physics program of the LHC at CERN is aimed at studying the quark-gluon plasma (QGP), a state of deconfined quarks and gluons that is formed in heavy-ion collisions. Jets, collimated bunches of particles originating from the fragmentation of a hard-scattered parton emitted in the early stages of a collision, can be used as a tomographic tool to study the QGP. As the hard scattered parton traverses the plasma, it loses energy (`jet quenching') via elastic and radiative interactions with medium constituents. Therefore, modifications of jet properties observed in heavy-ion collisions can be used to deduce properties of the QGP.
This talk will give a brief introduction to `hard probes', covering measurements of high-pt single particles and jets, and shows how a systematic comparison of models to experimental results can be used to extract transport parameters of the QGP. Parton energy loss mechanisms are explored via measurements of recoil jet yields and the event-plane dependence of jet production. Modifications of the parton shower itself are studied using jet shape observables, to more directly quantify medium effects on fragmentation. Special attention will be given to the experimental challenges posed by reconstructing jets in the presence of the large and strongly fluctuating background that is present in heavy-ion collisions.
Open heavy-flavour physics
The large interest in open heavy-flavour physics in heavy-ion collisions is proven by the flourishing results obtained at both RHIC and LHC energies. Because of their large masses, heavy quarks are produced in the early stages of heavy-ion collisions and their abundance is not expected to change throughout the evolution of the system. Hence, they behave as self-generated probes that traverse the hot and dense medium created in high-energy heavy-ion collisions, also called Quark Gluon Plasma (QGP). The study of heavy quarks allows us to probe different stages of the evolution of the heavy-ion collision: (i) in the initial stages, by testing pQCD and the nuclear PDF; (ii) in the QGP phase, since they interact with the medium losing energy via subsequent elastic scatterings and/or gluon radiation and can experience the collective motion of the system, providing information on the QGP properties; (iii) in the hadronization stage, as they provide a test for hadronization mechanisms such as fragmentation and coalescence. The RHIC and LHC experiments provide complimentary measurements of heavy-flavour particles in different kinematical coverages exploiting different experimental techniques. The heavy-flavour measurements based on the exclusive reconstruction of charmed mesons, semi-inclusive leptonic decays of charm and beauty as well as beauty-tagged jets will be discussed for pp, p+A and A+A collisions. The RHIC and the LHC Run 1 results indicate a strong "quenching" of heavy-quark production due to energy loss in the medium. In addition, the measurements of the azimuthal anisotropies of heavy-flavour particles suggest that charm quarks participate into the collective motion of the system. The recent measurements from the LHC Run 2 at the highest collision energy also confirm with improved precision the medium effects on heavy-quark production. I will review the most recent experimental results on heavy flavours from RHIC and LHC, which are starting to constrain theoretical models addinginformation on the QGP properties.
Tennessee Tech University
Studying the structure of neutron-rich deformed nuclei via beta decay
Deformation in nuclei appears to be the norm as it is observed all over the chart of nuclides. Yet, some nuclei tend to shy away from the norm and display abrupt changes in their nuclear shape in unexpected regions of the nuclear chart. A few of these puzzling cases have been studied for decades and still present a challenge to both nuclear theory and experiment.
This talk will outline some of the principles of beta decay and gamma-ray spectroscopy that are used to experimentally study the structure of these exotic nuclei. The focus will be on exotic neutron-rich nuclei which exhibit abrupt changes in their structure that are characterized by nuclear deformation. We will explore the versatility and use of nuclear spectroscopy techniques by way of two examples; one is the case of 33-35Al isotopes populated from the beta-decay of 33-35Mg and the second is 98Rb decaying to 98Sr. For the second example, we will further employ the use of lasers to enhance the nuclear spectroscopy techniques and capitalize on the unique characteristics of beta decay to decipher the structure of 98Sr and the nuclear shape-coexistence that it displays.
Shape coexistence and the role of reflection and axial asymmetry in nuclei
Understanding the nature of the fundamental interactions between protons and neutrons, and how they are organized within the nucleus continues to be one of the main research frontiers of nuclear science. Major progress in this quest have been possible due to advances in detector technologies that have allowed the exploration of regions far beyond the valley of beta stability. In this talk, I will discuss how experiments designed to study the most basic property of the nucleus, i.e., the shape, have advanced our understanding of the nuclear system. In particular, I will present results of our recent measurements using projectile Coulomb excitation to study the various shape degrees of freedom and associated phenomena that are capable of providing answers to current open questions in both nuclear structure and fundamental interactions. The talk will focus primarily on the the electromagnetic properties of low-lying states in 72,76Ge and 144Ba which were investigated via multistep Coulomb excitation measurement using the advanced gamma-ray tracking array, GRETINA and the charged particle detector, CHICO2. The influence of reflection symmetry and axial asymmetry on the shape of these nuclei along with the results of multi-configuration mixing calculations carried out within the framework of the triaxial rotor model will highlighted.
The birth of elements through nuclear decay in stellar furnaces
Half of all atomic elements heavier than iron are produced in the particular conditions occurring during stellar death. In the rapid neutron capture process, or r-process, neutrons from the stellar environment are quickly absorbed by stable nuclei. The isotopes produced in these conditions have neutron-proton imbalances much larger than stable matter, with properties that can be difficult to predict. In particular, systematic deviations from theoretical models have been observed in their beta-decay half-lives. In this colloquium I will review my recent experimental and theoretical efforts to develop a new model of beta-decay for key r-process nuclei, called waiting points. It will be shown that, unexpectedly, the nuclear orbital structure favors neutron over gamma emission in 83,84Ga, resulting in shorter half-lives when compared to calculations using a global model of the nucleus. This effect is found to explain the beta-decay half-life discrepancies with global models for all r-process waiting points beyond neutron magic numbers.
Argonne National Laboratory
Weak-binding effects in atomic nuclei
A thorough understanding of atomic nuclei would not only show great progress in our knowledge about the primary forces governing our environment, it would also provide exciting answers to questions about the origins of the chemical elements and the limits of visible matter. In an attempt to gain a more complete description of strong force governing proton and neutron interactions, our recent work has focused on obtaining and scrutinizing systematic sets of nuclear data ranging from tightly bound systems (near stability) to loosely bound systems (near the limits of binding). Through this work, a simple effect, related to the weak-binding behavior of orbitals having no orbital angular momenta, has been identified as the responsible party for a large amount of the changes in the underlying shell structure of nuclei below mass 20. Discovery of this so-called weak-binding behavior, its far-reaching impact on the structure of heavier nuclei, and its relevance to state-of-the-art theoretical nuclear models, will be discussed.
Nuclear physics and astrophysics using decay of proton-rich nuclides
The β-decay of proton-rich nuclei is a powerful tool in nuclear science; it can be used to probe isospin asymmetries, and nuclear astrophysics. Large Qβ-values of these nuclei allow the population of bound excited states of the daughter and open charged particle emission channels. Some of these levels correspond to astrophysically significant resonances which cannot be measured directly due to the lack of intense radioactive beams. In order to determine the strengths of these resonances, and hence the reactions rates, the partial widths for the de-excitation of these levels via gamma and charged particle emission have to be known, as well as the energies, spins, and parities. During the last years our group at the NSCL measured the β delayed γ emission of several nuclear species (26P, 31Cl, and 20Mg) to reduce the uncertainties in the rates of key nuclear reactions affecting astronomical observables associated with novae and type I x-ray bursts. During this talk I will review these results and discuss their relevance to nuclear astrophysics. To measure the charged particle branches we developed a new gaseous detector. In the last part of my talk I will give an overview of the project and discuss its present status.
Mississippi State University
Low-energy nuclear reactions using EFT
Low-energy nuclear reactions play a crucial role in astrophysical models of the universe. Nuclear cross sections with reliable error estimates are needed to make accurate astrophysical predictions. The effective field theory (EFT) formulation of low-energy nuclear physics is a valuable tool that can provide systematic error estimates that become a necessity when experimental data become unavailable at astrophysical energies. Reaction calculations in few-nucleon systems and those involving halo nuclei will be described. Modern ab initio calculations increasingly use EFT to construct the microscopic interactions. Recently, EFT on a space-time lattice has been successful in describing alpha-nuclei. Reaction calculations using lattice EFT will be discussed.
COHERENT experiment at the SNS
COHERENT experiment at the SNS (ORNL) is aiming to detect in a first time CEvNS (Coherent Elastic Neutrino Nucleus Scattering). I will review why is it important to detect and accurately measure CEvNS as well as its relation to the nuclear physics. I will update the present status and future plans of this experiment.
UTK Nuclear Engineering
Advanced control for future nuclear reactors
The current fleet of baseload, light water-cooled nuclear power reactors are well controlled by a combination of simple Proportional-Integral (PI) control and programmed open-loop response. This approach works well for steady-state reactors that effectively operate as linear systems. Future reactors, however, will largely operate with significant nonlinearities. Several advanced reactor designs, such as liquid metal reactors, include intermediate coolant loops that introduce significant time delays. Many future reactors are expected to provide power peaking and load following to support deep penetration of renewable energy in the grid; this mode of operation introduces significant reactivity feedback effects that are largely avoided in steady-state reactors. A new control paradigm is needed for nuclear power plants to accommodate these new designs and concepts of operation. This presentation will present recent and current work in developing and evaluating advanced control algorithms for the future fleet of nuclear reactors in the US and abroad.
Symmetry-violating nucleon-nucleon interactions in effective field theories
Violations of discrete symmetries such as parity (P) and time-reversal (T) invariance in nuclear systems can be used as precision tests of our understanding of the Standard Model as well as in searches for physics beyond the Standard Model. While parity-violating interactions between quarks are well understood, their manifestation as forces between nucleons originates in a complex interplay of weak and nonperturbative strong interactions. These P-violating interactions can therefore be used as a test of our understanding of nonperturbative QCD. Ongoing and planned experiments, e.g., at the SNS at Oak Ridge National Laboratory, are mapping out this weak component of the nuclear force. I will describe the use of effective field theory methods to formulate a consistent framework for the description of symmetry-preserving and symmetry-violating forces between nucleons, and their application to few-nucleon systems. I will also discuss how the large-N expansion of QCD can provide important theoretical constraints on symmetry-violating nucleon-nucleon interactions.
Studying proton transfer reactions using the VANDLE neutron detector array
Single nucleon transfer reactions are powerful tools for the study of the nuclear structure of short-lived nuclei. The spectroscopic properties of unstable nuclei help to constrain nuclear structure models for more exotic nuclei. In inverse kinematics, proton transfer reactions, such as (d,n), may be used to study the properties of short-lived radioactive ion beams (RIBs). By measuring the outgoing neutron, it is possible to extract spectroscopic information about the single-particle proton states of the recoil nucleus in much the same way as probing the neutron states of the recoil using neutron transfer (d,p). With the development of new accelerator facilities, such as FRIB in the U.S., comes the need for new spectroscopic tools for use with RIBs. The versatile array of neutron detectors at low energy (VANDLE) is an array of plastic scintillator bars which are used to measure neutrons using a time-of-flight method. Like all plastic scintillators, VANDLE is sensitive to gamma rays in addition to neutrons. This typically results in high background rates for measurements with high external trigger rates. Previous VANDLE reaction measurements have been performed relying solely on the detection of a charged recoil. The use of discriminating recoil particle detectors, such as phoswich detectors, allow for the selection of a clean recoil tag by separating the recoil nucleus of interest from unreacted RIB components. This method significantly reduces the level of background and allows the study of reactions with lower cross-sections. Developments of low energy proton transfer measurements in inverse kinematics as well as recent (d,n) measurements using RIBs and stable beams will be presented.
Inclusive deuteron-induced reactions
Deuteron–induced reactions have long been used to probe single-particle aspects of nuclear spectra. Understanding the reaction mechanism is essential in order to disentangle direct reaction contributions (transfer and elastic breakup) from compound nucleus formation. Aside from providing valuable spectroscopic information about the nature of single-particle states in nuclei, the absorption of the neutron can be used at profit to study neutron–induced reactions in radio active isotopes with the surrogate reaction method in inverse kinematics. Within this context, we have recently developed a reaction formalism that integrates consistently the various reaction channels (elastic breakup, neutron transfer and neutron capture) present in deuteron–induced reactions. The reaction is described as a two-step process, namely the breakup of the deuteron followed by a propagation of the loose neutron in the target field. This field is modeled with an optical potential, and can account for the absorption of the neutron both in finite–width bound states and in the above neutron–emission threshold continuum states. The connection with structure models is essentially encoded in this neutron–target effective interaction, such as microscopic (coupled–clusters calculations) and dispersive, semi–microscopic (dispersive optical model) optical potentials. Within this context, a correct treatment of the non–locality of these interactions is important and under way. The ultimate goal is to provide a powerful tool (consistently integrating structure and reactions) to predict and analyze the single–nucleon structure (both above and below nucleon emission threshold) of the new isotopes expected to be available for experimentation in exotic beam facilities, as measured in nucleon transfer reactions.