Theses and Dissertations from UMD
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Item DIRECTED AND ELLIPTIC FLOW MEASUREMENTS: A COMPARISON BETWEEN THE PARTICIPANT AND SPECTATOR PLANES IN Pb+Pb COLLISIONS AT √sNN = 5.02 TeV WITH CMS AT THE LHC(2024) Lascio, Samuel Andrew; Mignerey, Alice C.; Chemistry; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Directed and elliptic flow of unidentified charged hadrons at mid-rapidity are measured as a function of transverse momentum (pT) and pseudorapidity (η) in ultra-relativistic PbPb collisions at √sNN = 5.02 TeV with the Large Hadron Collider (LHC) at CERN. The reaction plane (RP) angle is approximated using participants and spectator neutrons measured with the Compact Muon Solenoid (CMS) detector and the newly installed Spectator Reaction Plane Detector (SRPD), respectively. The SRPD is the latest addition to the existing Zero Degree Calorimeter (ZDC) designed to measure spectator neutrons +/- 140 m from the interaction point at CMS. The Event Plane (EP) Method is used to calculate the v1odd, v1even, and v2 harmonic flow parameters as functions of η and pT. The directed flow measurements using participants and spectators with CMS are compared and contrasted. Overall results are in good agreement between participants and spectators, however v1even(pT) measurements using spectators begin to show the opposite trend to those using participants at pT > 2 GeV/c. Results are compared to those obtained by A Large Ion Collider Experiment (ALICE), which is another experiment at the CERN LHC. Directed flow results do not agree with those obtained by ALICE. Additionally, the first elliptic flow measurements using the EP Method and mixed harmonics with the SRPD are reported. A slight asymmetry in v2(η) is observed using spectators. The elliptic flow results do agree with ALICE. Tracking efficiency as determined by the CMS collaboration is applied to the data and potential corruption as a result is discussed. Results strongly support continued use of the SRPD as a spectator neutron detector for reaction plane determination within the CMS ZDC.Item RADIATION CHEMISTRY IN PRESSURIZED WATER NUCLEAR REACTORS: H2 GENERATION BY 10B(n,α)7Li, AND THE REACTION OF BORATE WITH •OH(2023) Guerin, Steven James; Al-Sheikhly, Mohamad I; Material Science and Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Nuclear power plants (NPPs) are complex engineering systems, with malfunctions having enormous potential to lead to widespread and extreme impacts on society and the environment as a whole. Their safe operation depends on a multitude of factors such as intelligent planning, proper design, quality components, high-level safety operations, and economic viability. Due to requiring high temperature and high pressure of an NPP’s cooling fluid, one of the main concerns for further developing safe operating conditions and evaluating component lifetimes is improving our understanding on the issue of corrosion in nuclear systems. In the U.S., all commercially operated Pressurized Water nuclear Reactors (PWRs) are light-water reactors wherein their coolant waters can reach temperatures up to 350 °C. According to a report in 2005 in association with the U.S. Federal Highway Administration, an annual cost of $4.2 billion was directly attributed to corrosion in NPPs in 1998, out of a total $6.9 billion in the electrical utilities industry (Koch, et al., 2005). Boron is added into commercial PWR primary water in the form of boric acid as a soluble chemical neutron “shim” in order to compensate for fuel burnup and allow smooth long-term reactivity control. After a boron nucleus captures a thermal neutron and becomes unstable, the energy of the recoil ions resulting from its fission accounts for up to 33 % of the total dose to the primary water. This event is an important source for H2 and corrosive H2O2, so its product yields must be accurately included in models of the cooling water radiation chemistry. H2 produced in water from the 10B(n,α)7Li fission reaction has been measured up to 300 °C to aid in quantification of the corrosive H2O2 from the same reaction. Thermal energy neutrons from the Rhode Island Nuclear Science Center 2 MW reactor interacted with boric acid contained in N2O-saturated water in temperature-controlled high-pressure cells made from tubing of either titanium or zirconium alloy. After exposure for a minimum of one hour, the solution samples were extracted and sparged with argon. The H2 entrained by the sparging gas was sampled with a small mass spectrometer. A small amount of sodium was included in the boric acid solution so that after sparging, samples could be collected for 24Na activation measurements in a gamma spectrometer to determine the neutron exposure and thus the total energy deposited in solution. The G-value (µmol/J) for H2 production was obtained for water at a pressure of 25 MPa, over a temperature range from 20 °C to 300 °C. These results have been complemented with Monte Carlo N-Particle® (MCNP®) simulations in collaboration with the National Institute of Standards and Technology, and have been compared with previous experimental results at room temperature and simulated results up to 350 °C. Additionally, boric acid has thus far been accepted as a chemically nondisruptive additive, as it was confirmed long ago to have extremely low reactivity with the two main reactive species produced in reactor primary water by radiolysis, the solvated aqueous electron and the hydroxyl radical (e(aq)- and •OH). However, at the Electric Power Research Institute standard desired pH of 7.3 and the operational temperature of 350 °C, approximately 22% of the boron added in PWR primary water exists in the chemical form of the conjugate base, borate, not boric acid. Although borate was previously confirmed to have no appreciable reactions with e(aq)-, it was not adequately studied for reactions with •OH prior to this work. We have observed a clearly apparent reaction between borate and •OH. Current chemistry models are completely ignorant on both the existence of the resultant species and its reactions. The chemical reaction of [B(OH)4]- (borate) with •OH along with cross-reactions of the product species have been studied up to 200 °C to determine those reactions’ rate constants and the products’ spectra. The University of Notre Dame Radiation Laboratory’s 8 MeV electron linear accelerator (LINAC) was configured to perform pulse radiolysis with pulse widths between 4ns to 20ns providing doses between 5.5 Gy and 62 Gy. High-energy electrons from the LINAC interact with the borated solution which has been N2O-saturated and is continuously flowed through a 316 stainless-steel optical cell. The cell temperature was adjusted by resistive-heating silicon cartridges, and pressure was controlled by two syringe pumps to prevent boiling. The cell had two fused silica windows for transmitting light from a xenon arc lamp through the solution and out to a multichromatic spectrophotometer system. Time-resolved spectral data was obtained over nano- and micro-second timeframes, for wavelengths ranging from the deep UV and into the infrared spectrum (250 nm to 820 nm). The reaction rates and products’ spectra were then obtained by analyzing the data using computational aids, namely IGOR Pro by Wavemetrics and KinTek Explorer by KinTek Corp. The product species of the reaction between borate and •OH is conjectured to be •[BO(OH)3]-, on the basis of ab initio calculations, which likely reacts with boric acid or borate to form a polymer radical.Item DIRECTED FLOW MEASUREMENTS USING THE SPECTATOR PLANE WITH THE CMS DETECTOR IN THE 2018 PB-PB RUN AT √SNN = 5.02 TEV(2022) Adams, Eric Brian; Mignerey, Alice C; Chemistry; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The Compact Muon Solenoid (CMS) is used along with the Spectator Reaction PlaneDetectors (SRPD) to measure the directed flow signal, using spectator neutrons, in the 2018 √sNN = 5.02 TeV Pb-Pb run with the Large Hadron Collider (LHC) at CERN. The Hadron Forward detector (HF), along with the tracker, is also used to measure the directed flow signal but instead uses participant nucleons. The results from the CMS 2018 Pb-Pb spectator and participant measurements of the directed flow signal are compared. These are the first spectator plane directed flow measurements from the CMS detector. The results are compared to the Pb-Pb collisions as reported by the A Large Ion Collider Experiment (ALICE) collaboration in 2013 [1].Item Jet Production Cross Section Measurement In √ s = 5.02 Tev pp Collisions(2021) Baron, Owen David Cadwalader; Mignerey, Alice C; Chemistry; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The study of jets offers insights into the nature of the basic partons composing matter, and enables further studies into the nature of the universe. This analysis presents the double-differential production cross section of radius parameter R = 0.3 proton-proton jets in units of pseudorapidity and transverse momentum at √ s = 5.02 TeV, measured in the Compact Muon Solenoid detector at the Large Hadron Collider experiment located at CERN. Jets are reconstructed using Particle Flow and the anti-kT algorithms. The methodology of correcting the detector response through Jet Energy Corrections and Bayesian unfolding is described with a detailed explanation. The results from data recorded in CMS in 2015 are shown and compared with leading-order theory-based simulated PYTHIA8 Monte Carlo events.Item Nuclear Structure Studies of ${^78,80}$Ge and Adjacent Nuclei(2018) Forney, Anne Marie; Walters, William B; Chemistry; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The main topic of this thesis concerns the unusual features of the nuclear structure of $^{78}$Ge. The discovery of a sequence of levels separated by one unit of angular momentum for which the expected crossover transitions carrying two units of angular momentum are not observed. This result stands in contrast to the neighboring even-even Ge and Se nuclei, as well as the results of most model calculations. The level structures of adjacent $^{82,80}$Ge are also studied to place the results for $^{78}$Ge in context. Likewise, shell-model calculations are performed as comparisons with the structures for all three nuclei. The data come from experiments at Argonne National Laboratory using the Gammasphere detector array. These experiments are important because of the broad interest in the structure of $^{76}$Ge and neighboring nuclei, owing to a world-wide effort in the search for neutrinoless double $\beta$ decay. Owing to the unusual features of this level sequence, it is labelled as a $\kappa$ band, taken from the Greek word καινουργιος, meaning new. The results pose a challenge to theorists to find ways to develop models that can fit both these features, as well as the other aspects of the structure of $^{78}$Ge. In addition, this study is important determining why no sequence like this has been found in any of the adjacent nuclei.Item A Probe of Colored Medium Effects on Quarkonia Polarization in √s = 7 TeV pp collisions at CMS(2017) Ferraioli, Charles Christopher; Mignerey, Alice C; Chemistry; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The suppression of quarkonia mesons is one of the signature indications of the presence of a quark-gluon plasma, the colored, asymptotically free state of matter believed to have existed moments after the Big Bang, and recreated by colliding heavy-ions. Two S-wave charmonia states, the J/ψ and the ψ(2S), along with three S-wave bottomonia states, the Υ(1S), Υ(2S), and Υ(3S), have been studied in heavy-ion collisions at both the Relativistic Heavy Ion Collider and the Large Hadron Collider (LHC), showing clear sequential suppression patterns, with the most tightly bound states less suppressed than the others, relative to scaled proton-proton (pp) collisions. Yet, the results remain difficult to interpret, owing to a combination of complicated feed-down processes from P-wave χ states, as well as regeneration of quarkonia occurring well after the initial collision. Further, the basic production mechanism of quarkonia is still far from certain, leaving open the possibility that changing mechanisms could affect the scaling of pp yields. This thesis aims to be the first in a line of studies into the effects of a colored medium on the basic production mechanism of quarkonia by measuring quarkonia polarization. Polarization can be measured using the angular distributions of dimuons emanating from quarkonia decays, and the Compact Muon Solenoid detector is well suited for these measurements. The polarizations of the three Υ(nS) and two ψ(nS) states were measured versus event multiplicity using a dimuon data sample collected during the 2011 LHC run of √s = 7 TeV pp collisions, with a total integrated luminosity of 4.9 fb−1. The measurements were integrated over the available rapidity range, for transverse momentum up to 35 GeV/c. All quarkonia states showed small polarizations, which were cross checked across several reference frames, and are consistent with multiplicity-integrated analyses. In the states for which a precise measurement could be made, the J/ψ and the Υ(1S), there was no variation with multiplicity, but these states are strongly affected by feed-down, preventing any definitive conclusions. Ultimately, this study leads the way for a polarization measurement in heavy-ion collisions, which would provide a more decisive look into the affect of a colored medium on quarkonium production.Item Directed Flow In Heavy Ion Collisions at sqrt{s_NN}=2.76 TeV(2015) Gomez, Jaime Arturo; Mignerey, Alice L; Chemical Physics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The directed flow of charged particles at midrapidity is measured in Pb-Pb collisions at $\sqrt{s_{NN}}=2.76$ TeV relative to the collision Event Plane, defined by the participant plane using various subdetectors. The rapidity-even directed flow component is measured for the first time using an Event Plane weighted by the transverse momentum of the emitted charged hadrons and found to be largely independent of pseudorapidity with a sign change at transverse momenta $p_{T}$ between 1.2 and $1.7$ GeV/c. These results are compared to measurements made by two other experiments at the LHC. Combined with the observation from ALICE of a vanishing rapidity-even $p_{T}$ shift along the spectator deflection plane is strong evidence for dipole like initial density fluctuations in the overlap zone of the nuclei. These observations open new possibilities for investigation of the initial conditions in heavy-ion collisions with spectator nucleons.Item Elliptic flow at forward rapidity in sqrt(s_(NN)) = 200 GeV Au+Au collisions(2012) Richardson, Eric; Mignerey, Alice C.; Chemistry; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Forward rapidity elliptic flow (v2) of both unidentified charged hadrons and decay muons has been measured from √sNN = 200 GeV Au+Au collisions as a function of pseudorapidity (η), transverse momentum, and number of nucleon collision participants. The measurements were performed at Brookhaven National Laboratory's Relativistic Heavy Ion Collider using the PHENIX experiment's Muon Arm spectrometers, located at 1.2 < |η| 2.4. To identify hadrons, which consist mostly of pions, kaons, and protons, a longitudinal momentum cut was applied to tracks stopping in the shallow steel layers of the Muon Arms. Those particles traversing completely through the Muon Arms consist of mostly muons from pion and kaon decays. The standard event plane (EP) method was used to measure v2, whose accuracy was improved ∼20-25% by combining the measured EP angles of several detectors, instead of using the measured EP from a single detector. Additionally, a hit swapping technique was devised to optimize track cuts, estimate background, and apply a background correction. To investigate the ability of the Muon Arms to accurately measure unidentified hadron v2, a GEANT simulation was also undertaken. The forward rapidity v2 results show good agreement with mid-rapidity measurements for central collisions ( 20-30% centrality), indicating a longitudinally extended thermalized medium with similar eccentricity, at least out to the Muon Arm η region. Only when compared to very forward BRAHMS measurements (η ≈ 3) is a v2 suppression seen for central collisions. For increasingly peripheral collisions, a growing suppression in v2 is observed for the Muon Arm measurements compared to mid-rapidity, indicating increased changes in the medium properties of ever smaller systems. For peripheral collisions of the same/similar centralities, an increased suppression is observed toward forward η.