Browsing by Department "Physics"

The elastic electron-proton ($e-p$) scattering and the spectroscopy of hydrogen atoms are the two traditional methods to determine the proton charge radius ($r_{p}$). In 2010, a new method using the muonic hydrogen ($\mu$H)\footnote{A muonic hydrogen has its orbiting electron replaced by a muon.} spectroscopy reported a $r_{p}$ result that was nearly ten times more precise but significantly smaller than the values from the compilation of all previous $r_{p}$ measurements, creating the ``proton charge radius puzzle".

In order to investigate the puzzle,

the PRad experiment (E12-11-106\footnote{Spokespersons: A. Gasparian (contact), H. Gao, M. Khandaker, D. Dutta}) was first proposed in 2011 and performed in 2016 in Hall B at the Thomas Jefferson National Accelerator Facility, with both 1.1 and 2.2 GeV electron beams. The experiment measured the $e-p$ elastic scattering cross sections in an unprecedented low values of momentum transfer squared region ($Q^2 = 2.1\times10^{-4} - 0.06~\rm{(GeV/c)}^2$), with a sub-percent precision.

The PRad experiment utilized a calorimetric method that was magnetic-spectrometer-free. Its detector setup included a large acceptance and high resolution calorimeter (HyCal), and two large-area, high-spatial-resolution Gas Electron Multiplier (GEM) detectors. To have a better control over the systematic uncertainties, the absolute $e-p$ elastic scattering cross section was normalized to that of the well-known M$\o$ller scattering process, which was measured simultaneously during the experiment. For each beam energy, all data with different $Q^{2}$ were collected simultaneously with the same detector setup, therefore sharing a common normalization parameter. The windowless H$_2$ gas-flow target utilized in the experiment largely removed a typical background source, the target cell windows. The proton charge radius was determined as $r_{p} = 0.831 \pm 0.007_{\rm{stat.}} \pm 0.012_{\rm{syst.}}$~fm, which is smaller than the average $r_{p}$ from previous $e-p$ elastic scattering experiments, but in agreement with the $\mu$H spectroscopic results within the experimental uncertainties.

The $\eta$ meson is an interesting tool to study fundamental symmetries in Quantum Chromodynamics (QCD). In particular, its radiative decay width, $\Gamma\left(\eta\rightarrow\gamma\gamma\right)$, is an important quantity that can be predicted in the framework of Chiral Perturbation Theory. A precision measurement of this quantity would provide critical inputs to understanding the mixing of the $\eta$ and $\eta'$ mesons and extracting constants with wide-ranging applications in low-energy QCD. This decay width has been measured in the past using two different experimental techniques. The more popular technique utilized $e^{+}e^{-}$ collisions to produce $\eta$ mesons through electromagnetic interactions. Today, the Particle Data Group (PDG) averages the results of five such experiments to obtain their currently-accepted value of the decay width as: 0.515$\pm$0.018~keV. However the first measurement of this quantity was obtained from a fixed-target experiment that measured the cross section for photoproduction of $\eta$ mesons on a nuclear target via the Primakoff effect. Their result of 0.324$\pm$0.046~keV shows strong tension with the average of the collider measurements, motivating a new, high precision measurement using the Primakoff method.

For this purpose, the PrimEx-\textit{eta} experiment was conducted in Hall D of the Thomas Jefferson National Accelerator Facility (Jefferson Lab or JLab). The data is currently being analyzed to measure the differential cross section for the photoproduction of $\eta$ mesons on a liquid, $^{4}$He target. Preliminary results obtained from the analysis of the first phase of the PrimEx-\textit{eta} experiment show reasonable agreement with the currently-accepted PDG value of the radiative decay width. However, as will be discussed, there are many challenges to this precision measurement which must be studied before any results can be finalized and compared with previous measurements.

In parallel to the $\eta$ decay width measurement, the PrimEx-\textit{eta} experiment measured the total cross section for the fundamental, Quantum Electrodynamics (QED) process of Compton scattering from the atomic electrons inside the target. The results obtained from this measurement are in strong agreement with the next-to-leading order QED calculations, and the total combined uncertainties are below 3\% for incident photon energies between 7-10~GeV. In addition to providing the first precision measurement of the total Compton scattering cross section within this beam energy range, this measurement verifies the capability of the PrimEx-\textit{eta} experimental setup to perform absolute cross section measurements at forward angles, and serves as a reference process for the calibration of systematic uncertainties.

A measurement of the Standard Model cross section for the production of a single top quark in association with a $W$-boson from proton-proton collisions is presented. Collision data at a center-of-mass energy of 13 TeV totaling 139 inverse femtobarns collected by the ATLAS detector on the Large Hadron Collider is used to study the process. Binary classifiers trained using kinematic properties of observable particles are used to separate the signal process from a large top pair production background. A binned maximum likelihood fit is performed to extract the Standard Model cross section for the signal process, along with a secondary top pair cross section measurement and uncertainties related to object reconstruction with the detector and theoretical models. The measured cross section is the most precise measurement performed using the ATLAS detector and is in good agreement with the Standard Model prediction.

Experiments at Jefferson Lab have been conducted to extract the nucleon spin-dependent structure functions over a wide kinematic range. Higher moments of these quantities provide tests of QCD sum rules and predictions of chiral perturbation theory ($\chi$PT). While precise measurements of $g_{1}^n$, $g_{2}^n$, and $g_1^p$ have been extensively performed, the data of $g_2^p$ remain scarce. Discrepancies were found between existing data related to $g_2$ and theoretical predictions. Results on the proton at large $Q^2$ show a significant deviation from the Burkhardt-Cottingham sum rule, while results for the neutron generally follow this sum rule. The next-to-leading order $\chi$PT calculations exhibit discrepancy with data on the longitudinal-transverse polarizability $\delta_{LT}^n$. Further measurements of the proton spin structure function $g_2^p$ are desired to understand these discrepancies.

Experiment E08-027 (g2p) was conducted at Jefferson Lab in experimental Hall A in 2012. Inclusive measurements were performed with polarized electron beam and a polarized ammonia target to obtain the proton spin-dependent structure function $g_2^p$ at low Q$^2$ region (0.02$<$Q$^2$$<$0.2 GeV$^2$) for the first time. The results can be used to test the Burkhardt-Cottingham sum rule, and also allow us to extract the longitudinal-transverse spin polarizability of the proton, which will provide a benchmark test of $\chi$PT calculations. This thesis will present and discuss the very preliminary results of the transverse asymmetry and the spin-dependent structure functions $g_1^p$ and $g_2^p$ from the data analysis of the g2p experiment .

The J/ψ particle has been the source of much research since its

discovery in 1974. It provides an important probe of quantum

chromodynamics and has lead to many important insights into the

interactions of quarks and gluons in bound states. The rate of J/ψ

production was found to be much higher than expected at hadron

colliding experiments. Non-relativistic quantum chromodynamics was

developed in order to address these issues. This theory predicts a

strong spin-alignment not observed in data. All previous measurements

of J/ψ production have overlooked the hadronic environment the

J/ψ is produced in. This work is the first exploration of the

radiation surrounding J/ψ events measured at ATLAS at

√s=8 TeV. This is the first measurement of the

separation between the J/ψ and a matched jet and the second

measurement of the momentum fraction shared between the jet and the

J/ψ. These variables probe the radiation environment around the

J/ψ, and provide a new ways to understand quarkonia production.

The Standard model process of Coherent Elastic Neutrino-Nucleus Scattering (CEvNS), which was first predicted by Freedman in 1974, has recently been observed by the COHERENT collaboration on CsI and liquid argon targets. The result is a new way to build a compact neutrino detector which unlocks new channels to test the Standard Model. A semiconductor germanium detector, a technology that has been developed by many dark matter direct detection experiments due to its excellent energy resolution and low-energy thresholds, will also be deployed to ORNL in order to detect CEvNS as part of the next phase of the COHERENT experiment. One of the challenges is to understand the signature of neutrino-induced low-energy nuclear recoils in germanium. A measurement was carried out at the Triangle Universities Nuclear Laboratory (TUNL) to characterize the it response to low-energy nuclear recoils. A quenching factor of 14-20% for nuclear recoil energies between 0.8-4.9 keV in Ge was established. A long predicted smearing effect due to quenching was observed for the first time and estimated to be 0.024 at ~2 keVnr. Finally, the impact of this effect and the quenching factor on the expected CEvNS spectrum of the future Ge deployment is presented.

The neutral pion decays via chiral anomaly and this process historically led to the discovery of the chiral anomaly. The $\pi^0$ decay amplitude is among the most precise predictions of quantum chromodynamics (QCD) at low energy. However, the current experimental results are not commensurate with theoretical predictions. The Partical Data Group (PDG) average of the experimental results is $7.74\pm0.46$ eV, which is consistent with the chiral anomaly prediction (leading order). Recent theoretical calculations (NLO and NNLO) show an increase of about 4.5\% to the LO prediction with 1\% precision. As a result, a precise measurement of the neutral pion decay amplitude would be one of the most stringent tests of low energy QCD. PrimEx-II experiment measured the neutral pion decay amplitude via the Primakoff effect using two targets, silicon and $^{12}$C. The $\pi^0\rightarrow\gamma\gamma$ decay amplitude was extracted by fitting the measured cross sections using recently updated theoretical models for the process. The resulting value is $7.82 \pm 0.05(stat) \pm 0.10(syst)$ eV. With a total uncertainty of 1.8\%, this result is the most precise experimental estimation and is consistent with current theoretical predictions.

A search for new heavy resonances decaying to boson pairs (WZ, WW or ZZ) using 20.3 inverse femtobarns of proton-proton collision data at a center of mass energy of 8 TeV is presented. The data were recorded by the ATLAS detector at the Large Hadron Collider (LHC) in 2012. The analysis combines several search channels with the leptonic, semi-leptonic and fully hadronic final states. The diboson invariant mass spectrum is studied for local excesses above the Standard Model background prediction, and no significant excess is observed for the combined analysis. 95$\%$ confidence limits are set on the cross section times branching ratios for three signal models: an extended gauge model with a heavy W boson, a bulk Randall-Sundrum model with a spin-2 graviton, and a simplified model with a heavy vector triplet. Among the individual search channels, the fully-hadronic channel is predominantly presented where boson tagging technique and jet substructure cuts are used. Local excesses are found in the dijet mass distribution around 2 TeV, leading to a global significance of 2.5 standard deviations. This deviation from the Standard Model prediction results in many theory explanations, and the possibilities could be further explored using the LHC Run 2 data.

A search for supersymmetry in pair-produced gluinos decaying via top squarks to the lightest neutralino is presented. Events with multiple hadronic jets, of which at least three must be identified as originating from b-quarks, and large amounts of missing transverse energy in the final state, are selected for study. The dataset utilized encompasses proton-proton collisions with a center-of-mass energy of sqrt(s) = 13 TeV and integrated luminosity of 79.9 fb-1 collected by the ATLAS experiment at the LHC from 2015 to 2017. The search employs a parameterized boosted decision tree (BDT) to separate supersymmetric signal events from standard model backgrounds. New methods for optimal BDT parameter point selection and signal region creation, as well as new soft kinematic variables, are exploited to increase the search's expected exclusion limit beyond prior analyses of the same dataset by 100-200 GeV in the gluino and neutralino mass plane. No excess is observed in data above the predicted background, extending the previous exclusion limit at the 95% confidence level by 250 GeV to approximately 1.4 TeV in neutralino mass. The analytical and machine learning techniques developed here will benefit future analysis of additional Run 2 data from 2018.

A search for the resonant production of top quark pairs in

proton-proton collisions at a center-of-mass energy of 8~TeV is

presented.

The Large Hadron Collider delivered 14 inverse femtobarns of collision

data which were collected by the ATLAS detector.

The lepton plus jets final state is used, and the top pair invariant

mass spectrum is probed for local excesses above the Standard Model

background prediction.

No evidence for resonant top pair production is found.

95\% credibility limits are set on the cross section times branching

ratio of two signal benchmarks.

A narrow leptophobic topcolor $Z^\prime$ boson decaying to top quark

pairs and the Kaluza-Klein excitation of the gluon in a

Randall-Sundrum model are excluded for masses below 1.8 and 2.0~TeV,

respectively.

The expected sensitivity to new physics at ATLAS with proton-proton

collisions delivered by a High Luminosity Large Hadron Collider is

also presented.

The feasibility of analyses studying vector boson scattering, exotic

resonances, and an extended Higgs sector with up to 3000 inverse

femtobarns of integrated luminosity is investigated based on the fast

simulation of proton-proton collisions at a center-of-mass energy of

14~TeV.

The field of quantum transport studies electron motion at low temperatures in nanos-tructures. Exciting electron phenomenon can be engineered by combining device designs like quantum dots, Josephson junctions, and interferometers with materials which host physics such as various quantum Hall effects and superconductivity. Com- binations of these ingredients can be mixed to design a device which is then cooled down and has its I ́ V curves measured while tuning key physical parameters, such as magnetic field, temperature, and gate electrode voltages. These time independent (DC) measurements can provide a wealth of information, but ultimately they can only access highly averaged physical properties. Fortunately, this is not a fundamental constraint. By measuring the emission of and response to higher frequency signals, we are able to access additional properties of our devices. This dissertation explores two projects related to time oscillating (AC) measure- ments of graphene devices with superconducting contacts. The first project is related to the measurement of “Shapiro steps” in graphene based Josephson junctions. By applying a gigahertz drive to the junction, it becomes possible to probe the dynamics of the phase difference of the junction. The work presented here explores the effects of the RF environment on the Shapiro step pattern, and on a bistability observed in this system. The second project addresses the noise measured downstream of a superconduct- ing contact for a device in the quantum Hall regime. Recent work has observed the coupling of superconductivity to a quantum Hall edge, a promising test-bed for mix- ing superconductivity with topological physics. However, the signal in real devices remains fairly small compared to the ideal limit. Noise measurements should allow us to probe the microscopics in these devices, but we find indications that signals seemingly related to contact heating obscure the desired signal. Additional devices which should show a tunable signal amplitude show only very small signal variation, opening questions about what physical phenomena may be suppressing this noise.

Any type of microscopy faces the problem in an attenuated signal level and reduced optical resolution due to optical aberration. To overcome this problem, adaptive optics was implemented in a two-photon fluorescence microscope. Using a “sensorless” approach, this study corrected the aberration in the system using two different excitation colors. As methodology, the point spread function was compared before and after applying adaptive optics. This study demonstrated that adaptive optics improves the resolution of the microscope for both excitation wavelengths. The aberration correction was then monitored as a function of depth. The result showed an improvement in the optimization metric as imaging depth is increased. Thus, adaptive optics offers improved imaging of the sample at deeper depths with better optical resolution and higher signal-to-noise ratio.

Complex artificial materials (metamaterials) strongly interact with light and can be used to fabricate structures which mimic a material response that has no natural equivalent. Classical tools for the design of optical or radio frequency devices are often ill-suited to utilize such media or have shortcomings in their ability to capture important physics in the device behavior. Recently it has been demonstrated that the structure of Maxwell's equations can be used to exploit this newly available freedom. By leveraging the `form-invariance' of Maxwell's equations under coordinate transforms, it is possible to develop material distributions in which light will behave as though flowing through warped coordinates. This design process is termed `transformation optics' and has inspired the creation of many novel electromagnetic structures such as the invisibility cloak.

In this dissertation the tools used in the field of transformation optics will be explored and expanded. Several new designs are discussed, each of which expands upon the ideas that have previously been employed in the field. To begin, I show that the explicit use of a transformation which extends throughout all space may be used to reduce the overall size of an optical device without changing its optical properties. A lens is chosen as a canonical device to demonstrate this behavior. For this work I provided the original idea for a compressing transformation as well as its dielectric-only implementation. I then mentored Dan Roberts as he confirmed the device properties through simulation. I further demonstrate that currents may be succesfully employed within the framework of transformation optics-resulting in novel antenna designs. For this work I suggested handling the sheet currents as the limit of a volumetric current density. I also demonstrated how an intermediate coordinate system could be used to easily handle the types of transformatios which were being explored.

For a particular functionality the choice of transformation is, in general, not unique. It is natural, then, to seek optimized transformations which reduce the complexity of the final structure. It was recently demonstrated that for some transformations a numerical scheme could be employed to find quasi-conformal transformations for which the requisite complex material distribution could be well approximated by an isotropic, inhomogeneous media. This process was previously used to demonstrate a carpet cloak-a device which masks a bump in a mirror surface. Unlike the more common transformation optical media, which exhibit strong losses at high frequencies, isotropic designs can be readily made to function at infrared or even optical frequencies.

The prospect of leveraging transformation optics in devices which operate at high frequencies, into the infrared and visible, motivates the use of quasi-conformal transformations in lens design. I demonstrate how transformation optics can be used to take a classical lens design based on spherical symmetry, such as a Luneburg lens, and warp it to suit the requirements of a planar imaging array. I report on the experimental demonstration of this lens at microwave frequencies. In the final design a lens is demonstrated in a two-dimensional field mapping waveguide to have a field of view of ~140 degrees and a bandwidth exceeding a full decade. In this work I proposed the idea of using the inverse of the quasi-conformal transform to arrive at the lens index profile. I performed all necessary simulations and wrote ray tracing code to confirm the properties of the lens. I proposed the metamaterial realization of the lens and performed the necessary retrievals for material design. I wrote code which would create the layout for an arbitrary gradient index structure in a standard computer aided drafting format. I fabricated three lenses-two of which are described in this thesis-and took all of the data shown in the thesis.

The most well known example of a transformation optical device is the invisibility cloak. Despite the great deal of attention paid to the cloak in the literature, the most natural way in which to quantify the efficacy of the cloak-its cross-section-has never been experimentally determined. This measurement is of practical interest because the cloak provides a useful canonical example of a medium which relies on the unique properties of metamaterials-strong anisotropy, inhomogeneity and both magnetic and electric response. Thus, a cloaking cross-section measurement provides a useful way to quantify advancements in the effective medium theories which form the basis for metamaterials. I report on the first such measurements, performed on the original microwave cloaking design. The experiments were carried out in a two-dimensional TE waveguide. Explicit field maps are used to determine the Bessel decomposition of the scattered wave. It is found that the cloak indeed reduces the scattering cross-section of a concealed metal cylinder in a frequency band from 9.91 to 10.14 GHz. The maximum cross-section reduction was determined to be 24%. The total cross-section and the Bessel decomposition of the scattered wave are compared to an analytical model for the cloaking design which assumes a discrete number of loss-less, homogenized cylinders. While the qualitative features of the cloak-a reduced cross-section at the cloaking frequency-are realized, there is significant deviation from the homogenized calculation. These deviations are associated with loss and inaccuracies of the effective-medium-model for metamaterials. In this work I proposed of direct integration of the fields to perform cross-section measurements. I worked out the necessary formulas to determine the coefficients in the Bessel expansion and the resulting scattering cross-section. I mentored an undergraduate student, Dan Gaultney, who scripted the application of the cross-section analysis and took the necessary data. All of the data in this thesis, however, is based on my own implementation of the data analysis.

In this thesis I discuss an alternative approach for investigating quarkonium production in hadron colliders. I present a complete framework for developing observables for studies of charmonium states produced within a jet. My work is based on the use of effective field theories of quantum chromodynamics that allow for the approximate factorization of jet cross sections in perturbative calculable terms and universal non-perturbative functions that are extracted from data. Particularly in this thesis I explore the factorization approach of non-relativistic quantum chromodynamics and soft-collinear effective theory. The fragmenting jet functions play central role in factorization theorems for cross sections for identified hadrons within jets. This cross sections can depend on the hadron-jet energy ratio and possibly on other jet observables. I expand this concept to jet-shape observables known as angularities and introduce the transverse momentum dependent fragmenting jet functions. Applications of these advanced methods to J/ψ production from gluon fragmentation in electron-positron annihilation are presented and I develop the tools for expanding this work in hadron colliders. Additionally, I compare predictions for J/ψ production in jets, based on the framework of fragmenting jet functions, against recent experimental data from the LHCb collaboration.

What affects the transition of a collection of grains from flowing to a rigid packing? Previous efforts towards answering this important question have led to various versions of ``jamming’’ phase diagrams, which specify conditions under which a granular material behaves like solid, i.e., in a jammed phase. In this dissertation, we report two sets of experiments to study the influence of particle shape and of the form of the applied shear strain on the jamming phase diagram of slowly deformed frictional granular materials. We use 2d photoelastic particles to measure the overall pressure of the system and various physical quantities that characterize the contact network such as the averaged number of contacts per particle.

In the first set of experiments, we systematically compare the mechanical and geometrical properties of uniaxially compressed granular materials consisting of particles with shapes of either regular pentagon or disk. The compression is applied quasi-statically and induces a density-driven jamming transition. We find that pentagons and disks jam at similar packing fraction. At the onset of jamming, disks have contact numbers consistent with predictions from an ideal constraint counting argument. However, this argument fails to predict the right contact number for pentagons. We also find that both jammed pentagons and disks show the Gamma distribution of the Voronoi cell area with the same parameters. Moreover, jammed pentagons have similar translational order for particle centers but slightly less orientational order for contacting pairs compared to jammed disks. Finally, we report observations that for jammed pentagons, the angle between edges at a face-to-vertex contact point shows a uniform distribution and the size of a cluster connected by face-to-face contacts shows a power-law distribution.

In the second set of experiments, we use a novel multi-ring Couette shear apparatus that we developed to eliminate shear banding which unavoidably appears in conventional Couette shear experiments. A shear band is a narrow region where a lot of rearrangements of particles occur. The shear band usually has a much smaller packing fraction than the rest of the system. We map out a jamming phase diagram experimentally, and for the first time perform a systematic direct test of the mechanical responses of the jammed states created by shearing under reverse shear. We find a clear distinction between fragile states and shear-jammed states: the latter do not collapse under reverse shear. The yield stress curve is also mapped out, which marks the stress needed for the shear-jammed states to enter a steady regime where many plastic rearrangements of particles happen and the overall stress fluctuates around a constant. Interestingly, for large packing fraction, a shear band still develops when the system remains strongly jammed in the steady regime. We find that the cooperative motion of particles in this regime is highly heterogeneous and can be quantified by a dynamical susceptibility, which keeps growing as the packing fraction increases.

Our observations not only serve as important data to construct theories to explain the origin of rigidity in density-driven jamming and shear-induced jamming but also are relevant to many other key problems in the physics of granular matter from the stability of a jammed packing to the complex dynamics of dense granular flows.

The mass of the $W$ boson is one of the most important parameters in the

Standard Model. A precise measurement of the $W$ boson mass, together

with a precise measurement of the top quark mass, can constrain the

mass of the undiscovered Higgs boson within the Standard Model

framework or give a hint for physics beyond the Standard Model.

This dissertation describes a measurement of the $W$ boson mass

through its decay into a muon and a neutrino using

$\approx$ 2.2 fb$^{-1}$ of $\sqrt{s} = 1.96$ TeV $p\bar{p}$ data taken

with the CDF II detector at Fermilab. We measure the $W$ boson mass

to be ($80.374 \pm 0.015_{\rm stat.} \pm 0.016_{\rm syst.}$)

GeV/c$^2$. This result, when combined with the $W$ mass

measurement in the electron channel, leads to the single most

precise $m_W$ value and greatly constrains the possible mass

range of the undiscovered Higgs boson.

A simultaneous measurement of three Standard Model cross-sections using 4.7 inverse femtobarns of proton-proton collision data at a center-of-mass energy of 7 TeV is presented. Collision data were collected using the ATLAS detector at the Large Hadron Collider. The signal production cross-sections studied are for top quark pair production, charged weak boson pair production, and Drell-Yan production of tau lepton pairs with invariant mass greater than 40 GeV. A data sample is defined from events with isolated high-energy electron-muon pairs arranged in a phase space defined by missing transverse momentum and jet multiplicity. A binned maximum likelihood fit is employed to determine signal yields in this phase space. Signal event yields are in turn used to measure full cross-section values and cross-section values within a fiducial region of the detector, and unlike conventional measurements the signal measurements are performed simultaneously. This is the first such simultaneous measurement of these cross-sections using the ATLAS detector. Measured cross-sections are found in good agreement with the most precise published theoretical predictions.



Giant multipole resonances are a fundamental property of nuclei and

arise from the collective motion of the nucleons inside

the nucleus. Careful studies of these resonances and their properties provides

insight into the nature of nuclear matter and constraints

which can be used to test our theories.

An investigation of the Isovector Giant Quadrupole Resonance (IVGQR)

in ²⁰⁹Bi has been preformed using the High Intensity γ-ray

Source (HIγS) facility. Intense nearly monochromatic

polarized γ-rays were incident upon a ²⁰⁹Bi target producing

nuclear Compton scattered γ-rays that were detected using the HIγS

NaI(Tl) Detector Array (HINDA). The HINDA array consists of six

large (10''x10'') NaI(Tl) core crystals, each surrounded by an

optically segmented 3'' thick NaI(Tl) annulus. The scattered γ-rays

both parallel and perpendicular to the plane of polarization were

detected at scattering angles of 55° and 125° with

respect to the beam axis. This was motivated by the realization that

the term representing the interference between the electric dipole

(E1) and electric quadrupole (E2) amplitudes, which appears in the

theoretical expression for the ratio of the polarized cross sections,

has a sign difference between the forward and backward angles and also

changes sign as the incident γ-ray energy is scanned over the E2

resonance energy. The ratio of cross sections perpendicular and

parallel to the plane of polarization of the incident γ-ray were

measured for thirteen different incident γ-ray energies between 15 and

26 MeV at these two angles and used to extract the parameters of the

IVGQR in ²⁰⁹Bi.

The polarization ratio was calculated at 55° and

125° using a model consisting of E1 and E2 giant resonances as

well as a modified Thomson scattering amplitude. The parameters of the E1 giant

resonance came from previous measurements of the Giant Dipole

Resonance (GDR)

in ²⁰⁹Bi. The finite size of the nucleus was

accounted for by introducing a charge form factor in the (modified)

Thomson amplitude. This form factor was obtained from

measurements of the charge density in inelastic electron scattering

experiments.

The resulting curves were fit to the data by varying the

E2 parameters until a minimum value of the χ² was found.

The resulting parameters from the fit yield an IVGQR in ²⁰⁹Bi

located at E_res=23.0±0.13(stat)±0.25(sys) MeV

with a width of Γ=3.9±0.7(stat)±1.3(sys) MeV and a

strength of 0.56±0.04(stat)±0.10(sys) Isovector Giant

Quadrupole Energy Weighted Sum Rules (IVQEWSRs).

The ability to make precise measurements of the parameters of the

IVGQR demonstrated by this work opens up new challenges to both

experimental and theoretical work in nuclear structure. A detailed

search for the missing sum rule strength in the case of ²⁰⁹Bi should

be performed. In addition, a systematic study of a number of nuclei

should be studied with this technique in order to carefully examine

the A dependence of the energy, width and sum rule strength of the

IVGQR as a function of the mass number A. The unique properties of

the HIγS facility makes it the ideal laboratory at which to perform

these studies.

Such a data base will provide more stringent tests of nuclear

theory. The effective parameters of collective models can be fine

tuned to account for such precision data. This should lead to new

insights into the underlying interactions responsible for the nature

of the IVGQR. Furthermore, with the recent advances in computational

power and techniques, microscopic shell model based calculations

should be possible and could lead to new insights into the underlying

properties of nuclear matter which are responsible for the collective

behavior evidenced by the existence and properties of the IVGQR.

High quality type-II superconducting contacts have recently been developed for a variety of 2D systems, allowing one to explore superconducting proximity in the quantum Hall (QH) regime, which is one of the routes for creating exotic topological states and excitations. Here, we experimentally explore an interface between two prototypical phases of electrons with conceptually different ground states: the integer quantum Hall insulator and the s-wave superconductor. We find clear signatures of hybridized electron and hole states similar to chiral Majorana fermions, which we refer to as chiral Andreev edge states (CAES). They propagate along the interface in the direction determined by magnetic field and their interference can turn an incoming electron into an outgoing electron or a hole, depending on the phase accumulated by the CAES along their paths. However, the observed signals are small in comparison to theoretical predictions which calls for a better understanding of the limitations imposed by the physics of real materials. We then perform a systematic study of Andreev conversion in the QH regime. We find that the probability of Andreev conversion of electrons to holes follows an unexpected but clear trend: the dependencies on temperature and magnetic field are nearly decoupled. These trends unveil the loss and decoherence mechanisms of CAES. To complement our understanding of a QH-superconductor interface, we also study the thermal response under tens of nA current bias. We find that the superconductor is significantly overheated at low field in comparison to a similar-sized normal metal and the temperature distribution is not uniform. Our results demonstrate the existence of chiral edge states propagating along a QH-superconductor interface and interfering over a significant length. The study of the loss, decoherence and overheating of these states further paves the way for engineering topological superconductivity in exotic quantum circuits.

The production of heavy quarkonium in heavy ion collisions has been used as an important probe of the quark-gluon plasma (QGP). Due to the plasma screening effect, the color attraction between the heavy quark antiquark pair inside a quarkonium is significantly suppressed at high temperature and thus no bound states can exist, i.e., they ``melt". In addition, a bound heavy quark antiquark pair can dissociate if enough energy is transferred to it in a dynamical process inside the plasma. So one would expect the production of quarkonium to be considerably suppressed in heavy ion collisions. However, experimental measurements have shown that a large amount of quarkonia survive the evolution inside the high temperature plasma. It is realized that the in-medium recombination of unbound heavy quark pairs into quarkonium is as crucial as the melting and dissociation. Thus, phenomenological studies have to account for static screening, dissociation and recombination in a consistent way. But recombination is less understood theoretically than the melting and dissociation. Many studies using semi-classical transport equations model the recombination effect from the consideration of detailed balance at thermal equilibrium. However, these studies cannot explain how the system of quarkonium reaches equilibrium and estimate the time scale of the thermalization. Recently, another approach based on the open quantum system formalism started being used. In this framework, one solves a quantum evolution for in-medium quarkonium. Dissociation and recombination are accounted for consistently. However, the connection between the semi-classical transport equation and the quantum evolution is not clear.

In this dissertation, I will try to address the issues raised above. As a warm-up project, I will first study a similar problem: $\alpha$-$\alpha$ scattering at the $^8$Be resonance inside an $e^-e^+\gamma$ plasma. By applying pionless effective field theory and thermal field theory, I will show how the plasma screening effect modifies the $^8$Be resonance energy and width. I will discuss the need to use the open quantum system formalism when studying the time evolution of a system embedded inside a plasma. Then I will use effective field theory of QCD and the open quantum system formalism to derive a Lindblad equation for bound and unbound heavy quark antiquark pairs inside a weakly-coupled QGP. Under the Markovian approximation and the assumption of weak coupling between the system and the environment, the Lindblad equation will be shown to turn to a Boltzmann transport equation if a Wigner transform is applied to the open system density matrix. These assumptions will be justified by using the separation of scales, which is assumed in the construction of effective field theory. I will show the scattering amplitudes that contribute to the collision terms in the Boltzmann equation are gauge invariant and infrared safe. By coupling the transport equation of quarkonium with those of open heavy flavors and solving them using Monte Carlo simulations, I will demonstrate how the system of bound and unbound heavy quark antiquark pairs reaches detailed balance and equilibrium inside the QGP. Phenomenologically, my calculations can describe the experimental data on bottomonium production. Finally I will extend the framework to study the in-medium evolution of heavy diquarks and estimate the production rate of the doubly charmed baryon $\Xi_{cc}^{++}$ in heavy ion collisions.