Browsing by Author "Geurts, Frank"
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Item A Systematic Measurement of mu+mu- Production in p+p and p+Au Collisions at sqrt(sNN) = 200 GeV with the STAR Detector(2018-11-09) Brandenburg, James Daniel; Geurts, FrankMost of the matter around us today is made up of protons and neutrons, but in the first few moments of the universe the temperature and density were too high for tightly bound protons and neutrons to form. Instead of being bound inside protons and neutrons, quarks and gluons existed in a plasma-like fluid called the Quark Gluon Plasma (QGP). As the universe cooled and expanded, the matter that we have today began to form. An understanding of nuclear matter and the transition from QGP to normal matter (and vice versa) can in principle be ascertained from the fundamental theory of the strong interaction, Quantum Chromodynamics (QCD). In practice though, the current state-of-the-art calculations provide only limited information about the properties of QCD matter. The transition from normal matter to QGP can be studied in the laboratory using relativistic heavy-ion collisions like those produced by the Relativistic Heavy-Ion Collider (RHIC) at Brookhaven National Laboratory. Studying the QGP through heavy-ion collisions has its challenges though, since the created matter evolves through many stages before the final state particles can be detected. Learning about the earliest stages of the system requires penetrating probes, capable of carrying information from inside the medium out to the final state. Electromagnetic probes, such as leptons, are inert to the strong force. For this reason, they carry pristine information from all stages of the created medium. Dileptons (l+l-) are even more valuable, since the various production mechanisms and time periods of the system can be distinguished through the invariant mass of the pair. For instance, the suppression in production of heavy quark (charm and bottom) bound states, which can be identified through dileptons, has long been considered a direct probe of the QGP. At lower masses dileptons can be used to measure the spectrum of thermal radiation of the medium, acting as a "fireball thermometer". Dileptons are also linked to the phenomena of spontaneous chiral symmetry breaking (and its expected restoration inside the QGP) through the rho-meson which decays into dileptons. In this thesis, the first measurements of the dilepton invariant mass spectra through the dimuon (mu+mu-) channel with the Solenoidal Tracker at RHIC (STAR) are presented. The mu+mu- invariant mass spectra is measured in data from p+p collisions at sqrt(s) = 200 GeV and p+Au collisions at sqrt(sNN) = 200 GeV. The first measurement of the phi -> mu+mu- spectra at STAR is also measured in p+p collisions at sqrt(s) = 200 GeV. For these analyses novel muon identification techniques were developed to combat the contamination from hadrons and secondary muons resulting from weak decays. Techniques are presented for training and employing deep neural networks for the identification of muons and for the rejection of backgrounds. Data-driven techniques are presented for the measurement of muon-purity and for the estimation of physical backgrounds to the mu+mu- invariant mass spectra. The measurement of the mu+mu- invariant mass spectra in p+p and p+Au collisions is also compared with the expected dimuon yields from light hadron decays, open heavy flavor decays, and the Drell-Yan process. Finally, the potential for future dilepton measurements at STAR is discussed in light of the new datasets collected in the recent years.Item Electric conductivity of hot and dense nuclear matter(Elsevier, 2024) Atchison, Joseph; Han, Yiding; Geurts, FrankTransport coefficients play an important role in characterising hot and dense nuclear matter, such as that created in ultra-relativistic heavy-ion collisions (URHIC). In the present work we calculate the electric conductivity of hot and dense hadronic matter by extracting it from the electromagnetic spectral function, through its zero energy limit at vanishing 3-momentum. We utilise the vector dominance model (VDM), in which the photon couples to hadronic currents predominantly through the ρ meson. Therefore, we use hadronic many-body theory to calculate the ρ-meson's self-energy in hot and dense hadronic matter, by dressing its pion cloud with π-ρ, π-σ, π-K, N-hole, and Δ-hole loops. We then introduce vertex corrections to maintain gauge invariance. Finally, we analyze the low-energy transport peak as a function of temperature and baryon chemical potential, and extract the conductivity along a proposed phase transition line.Item Electron Energy Loss Spectroscopy and Optical Properties of Plasmonic Nanostructure(2015-04-15) Cao, Yang; Nordlander, Peter J.; Geurts, Frank; Halas, NaomiPlasmon is considered to be the incompressible self-oscillation of conducting electrons in small nanoparticles. A classical spring model could be used to describe plasmon’s behavior. Many different techniques have been applied to understand nanostructure’s plasmonic properties. Electron energy loss spectroscopy (EELS) is one of these tools, which is helpful for us to understand the interaction between fast moving electrons and nanomaterials. It could achieve very high spatial and energy resolution. Here, we develop a new finite-difference time-domain method to calculate EELS spectra and maps, which is based on a commercial software package “Lumerical”. The calculated results for different cases are compared with the well-known boundary element method (BEM) and show an excellent agreement. Our finite-difference time-domain (FDTD) method to calculate EELS spectra has further been proven really helpful by high-density plasmonic dimers’ experimental results. There are basically two different numerical techniques. One is based on finite difference method (FEM) and another is according to finite-difference time-domain method (FDTD). Both of them are very important to perform optical calculations in nanophotonics and plasmonics area. In general, they will try to solve Maxwell equations with many different boundary conditions numerically. Optical properties of nanomaterials are also very tremendous for us to understand plasmonics behavior in the external electromagnetic fields. We systematically performed FEM simulations for different dimensions’ split ring structure and identified each plasmon mode via induced charge plot. Later we also studied hollow Au Nanoshells: hollow Au-Ag Nanoshell and hollow Au-Co Nanoshell. The former showed the surprising in vivo instability in the near infrared region while the later has potential application in hot electron generation.Item Magnetospheric Model Performance During Conjugate Aurora(2014-04-23) Longley, William; Reiff, Patricia H.; Geurts, Frank; Chan, Anthony ArthurAt 16:40 UT on August 17th, 2001, the IMAGE satellite was in position to view an auroral storm in the Northern Hemisphere, while the POLAR satellite was simultaneously in position to view the storm in the Southern Hemisphere. For many low-latitude auroras, the precipitation maps along field lines from the Southern Hemisphere to the Northern Hemisphere. However, in this case, the IMF had a very strong dawn-dusk component which has been shown to make the polar cap shift towards the dusk in one hemisphere and towards the dawn in the other, but this has not yet been confirmed by simultaneous auroral imaging. Using the satellite images in the 130 nm to 160 nm wavelength range, we have been able to identify the Polar Cap Boundary in both hemispheres throughout the event, and calculated the Dawn-Dusk Offset, ∆L, in both hemispheres. We then found correlations of 0.90 in the Northern Hemisphere and 0.83 in the Southern Hemisphere between ∆L, ranging from 4 to 12 degrees during the event, and By, ranging from 20 to 32 nT during the event. ∆L also correlated well against IMF Clock Angle (ϴC) and the Epsilon parameter (ϵ=vB2sin[ϴC/2]) when using specific time averages of these parameters. The same methods are then applied to the compute Polar Cap Boundaries in the BATSRUS, OpenGGCM, and LFM-MIX models that were run to simulate the event. We find that none of the models accurately describe the observed open-closed field line boundary during this event, with BATSRUS tending to produce boundaries that are too ideal and symmetric, OpenGGCM producing boundaries that are highly distorted and random, and the LFM-MIX model always yielding low correlations between ∆L and the various solar wind parameters.Item Measurement of the Forward-Backward Asymmetry in the Production of B+ Mesons in p p-bar Collisions(2015-02-06) Hogan, Julie M; Corcoran, Marjorie D; Geurts, Frank; Semmes, StephenWe present a measurement of the forward-backward asymmetry in the production of B+ mesons, A_FB(B+), using B+ -> J/psi K+ decays in 10.4 inverse femtobarns of p p-bar collisions at sqrt(s) = 1.96 TeV collected by the D0 experiment during Run II of the Tevatron collider. A nonzero asymmetry would indicate a preference for a particular flavor, i.e., b quark or b-bar antiquark, to be produced in the direction of the proton beam. We extract A_FB(B+) from a maximum likelihood fit to the difference between the numbers of forward- and backward-produced B+ mesons, using a boosted decision tree to reduce background. Corrections are made for reconstruction asymmetries of the decay products. We measure an asymmetry consistent with zero: A_FB(B+) = [-0.24 +/- 0.41(stat) +/- 0.19(syst)]%. The standard model estimate from next-to-leading-order Monte Carlo is A_FB(B+) = [2.31 +/- 0.34(stat.) +/- 0.51(syst.)]%. There is a difference of approximately 3 standard deviations between this prediction and our result, which suggests that more rigorous determination of the standard model prediction is needed to interpret these results.Item Missing Energy Studies at the DØ Experiment(2013-07-24) Hogan, Julie; Corcoran, Marjorie D.; Baring, Matthew G.; Geurts, FrankMissing transverse energy is an important aspect of physics analyses at hadron collider detectors. While other particles can be identified by the energy they deposit in the detector, the presence of neutrinos and other theorized particles must be inferred by an energy imbalance. At the DØ experiment missing energy algorithms exist not only to calculate the missing energy in an event, but to distinguish between possible sources: detector measurement effects or unobserved particles. DØ scientists rely on these algorithms to produce reliable physics results. This thesis presents updates made in the past year to missing energy certification, the unclustered energy resolution, and the missing energy significance calculation. It describes a new processor which calculates missing momentum from tracks as well as development work toward an unclustered energy calibration.Item Search for Muonic Atoms and Dimuon Production in Heavy-Ion Collisions(2015-12-03) Xin, Kefeng; Geurts, Frank; Padley, Paul; Scott, DavidLeptons, e.g. muons, are ideal tools to explore the hot and dense matter created at heavy-ion collider experiments, because they have minimal final state interactions and as a result are able to preserve information of the hot medium. This thesis focuses on two leptonic physics results of the STAR experiment at Brookhaven National Lab – dimuons and muonic atom production. The first measurement of dimuon production at low invariant mass is presented, using data collected from Au + Au collisions at psNN = 200 GeV. An excess of the dimuon yield over known hadronic contributions in the mass region 0.2 - 0.55 GeV/c2 is found. This excess might be sensitive to modified ⇢ meson spectrum function in hot medium, which has been proposed to be related to chiral symmetry restoration. This thesis also presents the first search results of muonic atoms in heavy-ion collisions. Femtoscopic correlations indicate hadrons and muons are produced at the same space-time point, providing a signature of atom ionization at the detector beam pipe. Invariant mass signals are observed for Kμ and pμ atoms and their antimatter counterparts. The measured yields and a calculation from a coalescence model are found not in agreement, suggesting significant other sources in the calculation may be needed.Item Thermal dielectron measurements in Au+Au collisions at $\sqrt{s_{NN}}=$14.6, and 19.6 GeV with the STAR experiment(2024-04-15) Han, Yiding; Geurts, FrankDielectrons emitted during the evolution of the hot and dense QCD medium created in relativistic heavy-ion collisions offer an effective way to probe the medium properties, as they do not interact via the strong force. The rate of the dielectron emission is proportional to the medium's electromagnetic spectral function. In the dielectron invariant mass range from $400$ MeV/$c^{2}$ to $800$ MeV/$c^{2}$, the spectral function probes the in-medium $\rho$ meson propagator which is sensitive to the medium’s properties including the total baryon density and the temperature. Meanwhile, the low energy range of the spectral function provides information about the medium’s electrical conductivity. Therefore, by measuring thermal dielectron production, we can study the microscopic interactions between the electromagnetic current and the medium. The STAR experiment has recorded large datasets of Au+Au collisions during the Beam Energy Scan Phase-II (BES-II) program, spanning center-of-mass energies between $\sqrt{s_{NN}}=$ 3.0 and 19.6 GeV with detector upgrades that benefit the dielectron measurement via extended transverse momentum and rapidity coverages as well as enhanced particle identification capability. In this thesis, I will report on the measurements of thermal dielectrons produced in Au+Au collisions at $\sqrt{s_{\text{NN}}}=$ 14.6, and 19.6 GeV using the STAR experiment.