Physics Commons^™

Strong Electron-Boson Coupling In The Iron-Based Superconductor Bafe1.9pt0.1as2 Revealed By Infrared Spectroscopy, Zhen Xing, Shanta Saha, J. Paglione, M. M. Qazilbash

Arts & Sciences Articles

Understanding the formation of Cooper pairs in iron-based superconductors is one of the most important topics in condensed matter physics. In conventional superconductors, the electron-phonon interaction leads to the formation of Cooper pairs. In conventional strong-coupling superconductors like lead (Pb), the features due to electron-phonon interaction are evident in the infrared absorption spectra. Here we investigate the infrared absorption spectra of the iron arsenide superconductor BaFe1.9Pt0.1As2. We find that this superconductor has fully gapped (nodeless) Fermi surfaces, and we observe the strong-coupling electron-boson interaction features in the infrared absorption spectra. Through modeling with the Eliashberg function based on Eliashberg theory, …

Probe Of Electroweak Interference Effects In Non-Resonant Inelastic Electron-Proton Scattering, James Franklyn Dowd

Dissertations, Theses, and Masters Projects

The Qweak collaboration at Jefferson Lab made the first direct measurement of the proton's weak charge, Q_W^p, via a measurement of the parity-violating asymmetry in elastic e ⃑p scattering with low four-momentum transfer. to meet the high-precision goals, energy-dependent electroweak radiative corrections were applied to the measured asymmetry. The γZ box, □_γZ, where a photon and a Z-boson are simultaneously exchanged, was the most problematic of these corrections. It could not be calculated through the same perturbative methods as the rest of the corrections. The □_γZ correction depends on theoretical models of the γZ interference structure functions, F_1,2^γZ, for which …

Exotic Phases In Attractive Fermions: Charge Order, Pairing, And Topological Signatures, Peter Rosenberg

Dissertations, Theses, and Masters Projects

Strongly interacting many-body systems remain a central challenge of modern physics. Recent developments in the field of ultra-cold atomic physics have opened a new window onto this enduring problem. Experimental progress has revolutionized the approach to studying many-body systems and the exotic behaviors that emerge in these systems. It is now possible to engineer and directly measure a variety of models that can capture the essential features of real materials without the added complexity of disorder, impurities, or complicated or irregular geometries. The parameters of these models can be freely tuned with tremendous precision. These experimental realizations are an ideal …

A Measurement Of Nuclear Effects In Deep Inelastic Scattering In Neutrino-Nucleus Interactions, Anne Norrick

Dissertations, Theses, and Masters Projects

Neutrino-Nucleus Deep Inelastic Scattering (DIS) events provide a probe into the structure of nucleons within a nucleus that cannot be accessed via charged lepton-nucleus interactions. The MINERvA experiment is stationed in the Neutrinos from the Main Injector (NuMI) beam line at Fermi National Accelerator Laboratory. With the recent increase in average neutrino energy and the greatly increased intensity of the NuMI beam line, projected sensitivities for DIS cross section ratio analyses using MINERvA's suite of nuclear targets (C, CH, Fe and Pb) are greatly increased. an analysis of theMINERvA DIS data on carbon, iron, lead, and plastic has been conducted …

Dynamics Of Systems With Hamiltonian Monodromy, Daniel Salmon

Dissertations, Theses, and Masters Projects

A system is said to have monodromy if, when we carry the system around a closed circuit, it does not return to its initial state. The simplest example is the square-root function in the complex plane. A Hamiltonian system is said to have Hamiltonian monodromy if its fundamental action-angle loops do not return to their initial topological state at the end of a closed circuit. These changes in topology of angle loops carry through to other aspects of these systems, including the classical dynamics of families of trajectories, quantum spectra and even wavefunctions. This topological change in the evolution of …

Extensions Of The Standard Model Higgs Sector, Richard Keith Thrasher

Dissertations, Theses, and Masters Projects

The Standard Model is regarded as one of the most successful scientific theories, but there is compelling evidence that it is an incomplete theory of particle physics. There is currently no understanding of the observed baryon asymmetry, the nature of dark matter, and dark energy. Field theoretic considerations indicate parameters in the Standard Model are extremely fine-tuned. This suggests the existence of new physics, accessible at higher energies, to explain these seemingly unnatural tunings. to solve these puzzles, and others not addressed by the Standard Model, many extensions of the Standard Model have been proposed. It is of great importance …

Topological Changes Of Wave Functions Associated With Hamiltonian Monodromy, C. Chen, John B. Delos

Arts & Sciences Articles

Almost everything that happens in classical mechanics also shows up in quantum mechanics when we know where to look for it. A phenomenon in classical mechanics involves topological changes in action-angle loops as a result of passage around a “monodromy circuit.” This phenomenon is known by the short name “Hamiltonian monodromy” (or, more ponderously, “nontrivial monodromy of action and angle variables in integrable Hamiltonian systems”). In this paper, we show a corresponding change in quantum wave functions: These wave functions change their topological structure in the same way that the corresponding classical action-angle loops change.

Microwave Ac Zeeman Force For Ultracold Atoms, C. T. Fancher, A. J. Pyle, A. P. Rotunno, Seth Aubin

Arts & Sciences Articles

We measure the ac Zeeman force on an ultracold gas of 87Rb due to a microwave magnetic field targeted to the 6.8 GHz hyperfine splitting of these atoms. An atom chip produces a microwave near field with a strong amplitude gradient, and we observe a force over three times the strength of gravity. Our measurements are consistent with a simple two-level theory for the ac Zeeman effect and demonstrate its resonant, bipolar, and spin-dependent nature. We observe that the dressed-atom eigenstates gradually mix over time and have mapped out this behavior as a function of magnetic field and detuning. We …

Isotope Shifts In The 7 S → 8 S Transition Of Francium: Measurements And Comparison To Ab Initio Theory, M. R. Kalita, J. A. Behr, (...), Seth Aubin, Et Al.

Arts & Sciences Articles

We observe the electric-dipole forbidden 7s→8s transition in the francium isotopes 208−211Fr and 213Fr using a two-photon excitation scheme. We collect the atoms online from an accelerator and confine them in a magneto-optical trap for the measurements. In combination with previous measurements of the 7s→7p1/2 transition we perform a King plot analysis. We compare the thus-determined ratio of the field shift constants (1.228 ± 0.019) to results obtained from new ab initio calculations (1.234 ± 0.010).

Cosmogenic Neutron Production At Daya Bay, Daya Bay Collaboration, (…), R. D. Mckeown, W. Wang, Et Al.

Arts & Sciences Articles

Neutrons produced by cosmic ray muons are an important background for underground experiments studying neutrino oscillations, neutrinoless double beta decay, dark matter, and other rare-event signals. A measurement of the neutron yield in the three different experimental halls of the Daya Bay Reactor Neutrino Experiment at varying depth is reported. The neutron yield in Daya Bay's liquid scintillator is measured to be Y-n = (10.26 +/- 0.86) x 10(-5), (10.22 +/- 0.87) x 10(-5), and (17.03 +/- 1.22) x 10(-5) mu(-1)g(-1)cm(2) at depths of 250, 265, and 860 meters-water-equivalent. These results are compared to other measurements and the simulated neutron …

Searching For A Dark Photon In The Hps Experiment, Sebouh Jacob Paul

Dissertations, Theses, and Masters Projects

The Heavy Photon Search (HPS) experiment at Jefferson Lab is designed to search for a hypothesized elementary particle called a dark (heavy) photon. Such a particle would behave as a mediator between dark matter and the Standard Model through a kinetic mixing with the Standard Model’s photon. The search is performed by scattering GeV-scale electrons off tungsten nuclei in a fixed target and looking for a resonance and/or displaced vertices amidst a background of radiative QED trident events. These background events are kinematically identical to the events in which dark photons are produced and decay into lepton pairs. Several other …

Proton Spin Structure From Monte Carlo Global Qcd Analyses, Jacob Ethier

Dissertations, Theses, and Masters Projects

Although significant progress has been made in recent years in understanding the composition of the proton's spin from its quark and gluon constituents, a complete picture has yet to emerge. Such information is encoded in spin-dependent parton distribution functions (PDFs) that, as a consequence of being inherently nonperturbative, must be extracted through global QCD analyses of polarized lepton-nucleon and proton-proton collisions. Experiments that measure a final state hadron from these reactions are particularly useful for separating the individual quark and anti-quark polarizations, but require knowledge of parton-to-hadron fragmentation functions (FFs) to describe theoretically. In this thesis, we present a new …

Experimental Observation Of Classical Dynamical Monodromy, M. P. Nerem, D. Salmon, S. Aubin, John B. Delos

Arts & Sciences Articles

A Hamiltonian system is said to have nontrivial monodromy if its fundamental action-angle loops do not return to their initial topological state at the end of a closed circuit in angular momentum-energy space. This process has been predicted to have consequences which can be seen in dynamical systems, called dynamical monodromy. Using an apparatus consisting of a spherical pendulum subject to magnetic potentials and torques, we observe nontrivial monodromy by the associated topological change in the evolution of a loop of trajectories.

Isoscalar Pi Pi, K(K)Over-Bar, Eta Eta Scattering And The Sigma, F(0),F(2) Mesons From Qcd, Raul A. Briceno, Jozef J. Dudek, Robert G. Edwards, David J. Wilson

Arts & Sciences Articles

We present the first lattice QCD study of coupled isoscalar pi pi, K (K) over bar, eta eta S- and D-wave scattering extracted from discrete finite-volume spectra computed on lattices which have a value of the light quark mass corresponding to m(pi) similar to 391 MeV. In the J(P) = 0(+) sector we find analogues of the experimental sigma and f(0)(980) states, where the sigma appears as a stable bound-state below pi pi threshold, and, similar to what is seen in experiment, the f(0)(980) manifests itself as a dip in the pi pi cross section in the vicinity of the …

Experimental Observation Of Classical Dynamical Monodromy, M. P. Nerem, D. Salmon, Seth Aubin, John B. Delos

Arts & Sciences Articles

A Hamiltonian system is said to have nontrivial monodromy if its fundamental action-angle loops do not return to their initial topological state at the end of a closed circuit in angular momentum-energy space. This process has been predicted to have consequences which can be seen in dynamical systems, called dynamical monodromy. Using an apparatus consisting of a spherical pendulum subject to magnetic potentials and torques, we observe nontrivial monodromy by the associated topological change in the evolution of a loop of trajectories.

Detecting A Heavy Neutrino Electric Dipole Moment At The Lhc, Marc Sher, Justin R. Stevens

Arts & Sciences Articles

The milliQan Collaboration has proposed to search for millicharged particles by looking for very weakly ionizing tracks in a detector installed in a cavern near the CMS experiment at the LHC. We note that another form of exotica can also yield weakly ionizing tracks. If a heavy neutrino has an electric dipole moment (EDM), then the milliQan experiment may be sensitive to it as well. In particular, writing the general dimension-5 operator for an EDM with a scale of a TeV and a one-loop factor, one finds a potential EDM as high as a few times 10(-17) e-cm, and models …

Highly Repeatable Nanoscale Phase Coexistence In Vanadium Dioxide Films, T. J. Huffman, D. J. Lahneman, (...), M. M. Qazilbash

Arts & Sciences Articles

It is generally believed that in first-order phase transitions in materials with imperfections, the formation of phase domains must be affected to some extent by stochastic (probabilistic) processes. The stochasticity would lead to unreliable performance in nanoscale devices that have the potential to exploit the transformation of physical properties in a phase transition. Here we show that stochasticity at nanometer length scales is completely suppressed in the thermally driven metal-insulator transition (MIT) in sputtered vanadium dioxide (VO2) films. The nucleation and growth of domain patterns of metallic and insulating phases occur in a strikingly reproducible way. The completely deterministic nature …

Applications Of Lattice Qcd To Hadronic Cp Violation, David Brantley

Dissertations, Theses, and Masters Projects

Experimental tests of the Standard Model are reaching a precision in which they are probing beyond Standard Model parameter spaces. Increasingly precise experimental tests of the Standard Model (SM) require a concurrent theoretical push to provide ever more precise predictions to interpret experimental results. For example, future direct dark matter detection experiments, searches for Majorana neutrinos, and neutron electric dipole moment searches, all require a fundamental understanding of nuclear physics in the low-energy regime. Nuclear physics emerges from non-perturbative dynamics of the fundamental theory of the strong interaction, QCD, at low energies. Lattice QCD is currently our only systematically controllable …

Charge Dynamics In The Metallic And Superconducting States Of The Electron-Doped 122-Type Iron Arsenides, Zhen Xing

Dissertations, Theses, and Masters Projects

Understanding charge dynamics and the origin of superconductivity in iron-based materials is one of the most important topics in condensed matter physics. Among different structures of iron-based materials, 122-type iron arsenides are of considerable interest due to their diverse phase diagrams, relatively high superconducting transition temperatures, and the availability of high quality single crystals. In this dissertation, we study temperature and frequency dependence of charge dynamics of the electron-doped 122-type iron arsenides in the metallic and superconducting states using broadband infrared spectroscopy at cryogenic temperatures. We have investigated the charge dynamics and the nature of many-body interactions in metallic La- …

First Measurements Of The Parity-Violating And Beam-Normal Single-Spin Asymmetries In Elastic Electron-Aluminum Scattering, Kurtis David Bartlett

Dissertations, Theses, and Masters Projects

The Qweak collaboration has made the first measurements of the elastic parity-violating and beam-normal single-spin asymmetries from the 27Al nucleus. Both are the result of ancillary measurements conducted during the Qweak experiment at Jefferson Lab. The goal of the experimental was to determine the proton's weak charge, Qp W, via a measurement of the elastic parity-violating electron-proton scattering asymmetry. During the experiment, ancillary measurements were made with different beam configurations on a separate aluminum alloy target, in an effort to directly measure the aluminum background coming from the experiment's liquid hydrogen target cell.

This dissertation discusses three primary results: the …

Lattice Qcd For Neutrinoless Double Beta Decay: Short Range Operator Contributions, Henry Jose Monge Camacho

Dissertations, Theses, and Masters Projects

The Standard Model (SM), the fundamental theory of particle physics, very success- fully describes the world around us, and with a only a few tantalizing exceptions, all the experiments we have performed to understand the fundamental laws of nature. However, the SM accounts for only 4-5% of the matter and energy in the universe, with approxi- mately 25% composed of dark matter (DM) and the remaining 70% composed of the more mysterious dark energy. Further, the SM content of the universe is composed of an excess of matter over anti-matter of about 1 part per billion. Despite being a small …