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Hamad, Ayman I.AELLIPTIC FLOW STUDY OF CHARMED MESONS IN 200 GEV AU+AU COLLISIONS AT THE RELATIVISTIC HEAVY ION COLLIDER
PHD, Kent State University, 2017, College of Arts and Sciences / Department of Physics
Quantum Chromodynamics (QCD), the theory of the strong interaction between quarks and gluons, predicts that at extreme conditions of high temperature and/or density, quarks and gluons are no longer confined within individual hadrons. This new deconfined state of quarks and gluons is called Quark-Gluon Plasma (QGP). The Universe was in this QGP state a few microseconds after the Big Bang. The Relativistic Heavy Ion Collider (RHIC) at Brookhaven National Laboratory (BNL) on Long Island, NY was built to create and study the properties of QGP. Due to their heavy masses, quarks with heavy flavor (charm and bottom) are mainly created during the early, energetic stages of the collisions. Heavy flavor is considered to be a unique probe for QGP studies, since it propagates through all phases of a collision, and is affected by the hot and dense medium throughout its evolution. Initial studies, via indirect reconstruction of heavy flavor using their decay electrons, indicated a much higher energy loss by these quarks compared to model predictions, with a magnitude comparable to that of light quarks. Mesons such as D0 could provide information about the interaction of heavy quarks with the surrounding medium through measurements such as elliptic flow. Such data help constrain the transport parameters of the QGP medium and reveal its degree of thermalization. Because heavy hadrons have a low production yield and short lifetime (e.g. ct = 120µm for D0), it is very challenging to obtain accurate measurements of open heavy flavor in heavy-ion collisions, especially since the collisions also produce large quantities of light-flavor particles. Also due to their short lifetime, it is difficult to distinguish heavy-flavor decay vertices from the primary collision vertex; one needs a very high precision vertex detector in order to separate and reconstruct the decay of the heavy flavor particles in the presence of thousands of other particles produced in each collision. The STAR collaboration built a new micro-vertex detector and installed it in the experiment in 2014. This state-of-the-art silicon pixel technology is named the Heavy Flavor Tracker (HFT). The HFT was designed in order to perform direct topological reconstruction of the weak decay products from hadrons that include a heavy quark. The HFT consists of four layers of silicon, and it improves the track pointing resolution of the STAR experiment from a few mm to around 30 µm for charged pions at a momentum of 1 GeV/c. In this dissertation, I focus on one of the main goals of the HFT detector, which is to study the elliptic flow v2 (a type of azimuthal anisotropy) for D0 mesons in Au+Au collisions at vsNN = 200 GeV. My analysis is based on the 2014 data set (about 1.2 billion collisions covering all impact parameters) that include data from the HFT detector. There are two new and unique analysis elements used in this dissertation. First, I performed the analysis using a Kalman filter algorithm to reconstruct the charmed-meson candidates. The standard reconstruction is via a simple helix-swim method. The advantage of using the Kalman algorithm is in the use of the full error matrix of each track in the vertex estimation and reconstruction of the properties of the heavy-flavor parent particle. Second, I also used the Tool for Multivariate Analysis (TMVA), a ROOT-environment tool, to its full potential for signal significance optimization, instead of the previous approach based on a set of fixed cuts for separating signal from background. This dissertation presents the elliptic component (v2) of azimuthal anisotropy of D0 mesons as a function of transverse momentum, pT . The centrality (impact parameter) dependence of D0 v2(pT) is also studied. Results are compared with similar studies involving light quarks, and with the predictions of several theoretical models.

Committee:

Spyridon Margetis, Prof. (Advisor); Declan Keane, Prof. (Advisor); Veronica Dexheimer (Committee Member); Songping Huang (Committee Member); Mietek Jaroniec (Committee Member)

Subjects:

Nuclear Physics; Particle Physics; Physics

Keywords:

Nuclear Physics; Heavy Ion Collisions; Relativistic Heavy Ion Collider; Quark Gluon Plasma; Heavy Flavor quarks; Heavy Flavor Tracker Detector; Azimuthal Anisotropy

Pandit, YadavAZIMUTHAL ANISOTROPY IN HEAVY ION COLLISIONS
PHD, Kent State University, 2012, College of Arts and Sciences / Department of Physics
STAR (Solenoidal Tracker At RHIC) is one of two large detectors along the ring of the Relativistic Heavy Ion Collider (RHIC) at Brookhaven National Laboratory. Experiments that collide heavy nuclei at high energy have been taking data at RHIC since the year 2000. The main goal of RHIC has been to search for a new phase of matter called the Quark Gluon Plasma (QGP), and to determine its properties, including the phase diagram that governs the relationship between QGP and more conventional hadronic matter. This dissertation has a particular focus on analysis of STAR measurements of the anisotropy of particle emission over a range of colliding energies, and these particular measurements are made possible by a unique application of a detector subsystem called Beam-Beam Counters (BBCs), which are placed close to the beam lines on both sides of the collision region. This project has involved development of software that uses the hit pattern of charged particles in the BBCs to determine the collision reaction plane, for use in measurements of anisotropy. Anisotropic flow sheds light on the early partonic system, and according to models, is minimally distorted during the post-partonic stages of the collision. In this anisotropic flow analysis, the estimated reaction plane of each event is reconstructed using the BBC signals, which have a large rapidity gap between them. There is also a large rapidity gap between each BBC and the STAR Time Projection Chamber (the main STAR subsystem for measuring particle tracks). These large rapidity gaps allow us to measure correlations relative to the reaction plane with the least possible systematic error from what is known as “non-flow”, i.e., background correlations unrelated to the reaction plane. Flow correlations are normally reported in terms Fourier coefficients, v1, v2, etc. Di- rected flow is quantified by the first harmonic (v1) in the Fourier expansion of the particle’s azimuthal distribution with respect to the reaction plane. Elliptic flow is the name given to the second harmonic (v2), and triangular flow is the name for the third harmonic (v3). These harmonic coefficients carry information on the very early stages of the collision. The v1 component is emphasized in this dissertation, and the BBC information that is a unique feature of this work is especially important for v1 measurements. Until recently, higher-order odd harmonics were overlooked. These odd flow harmonics carry valuable information about the initial-state fluctuations of the colliding system. This dissertation includes a study of the flow harmonic related to dipole asymmetry and triangularity in the initial geometry.

Committee:

Declan Keane, Dr. (Committee Chair); Spyridon Margetis, Dr. (Committee Member); Bryon Anderson, Dr. (Committee Member); Antal I. Jakli, Dr. (Committee Member); Mark L. Lewis, Dr. (Committee Member)

Subjects:

Nuclear Physics

Keywords:

Heavy ion collisions; collective motion; flow; azimuthal anisotropy; phase transition; QGP

Kuhlman, Anthony JosephThe beginning and end of heavy ion collisions: using uranium beams and Bose-Einstein correlations as probes of the collision fireball
Doctor of Philosophy, The Ohio State University, 2007, Physics
In this work, we begin by examining the possibility of using collisions between large deformed nuclei, such as uranium, at the Relativistic Heavy Ion Collider (RHIC) facility at Brookhaven National Laboratory. We present calculations that highlight the advantages of such an endeavor over the current gold-gold (Au+Au) program. These calculations are examined both within a Glauber model framework and using a color glass condensate (CGC) type picture. We discuss event selection techniques and analyze these procedures using a Monte Carlo simulation. We also explore the use of two-particle interferometry to probe the final size and shape of the particle emitting source. We develop a computer program capable of computing the azimuthally dependent spatial correlation tensor and Hanbury Brown-Twiss (HBT) radii. The accuracy of this program is tested by comparing its output with a number of analytic calculations. We then employ symmetries of the source function to greatly reduce the computational effort necessary to evaluate the Fourier expansions of the correlation tensor and the HBT radii. We close by examining the effects of final state interactions on the measured HBT radii. We derive a nonrelativistic expression for the two-particle probability and examine this expression in various limits, assuming a time-independent interaction with the medium. We explore the effects of weak rescattering on the measured radii by performing a perturbative calculation in the case with only a time-independent medium interaction, obtaining a surprisingly straightforward result.

Committee:

Ulrich Heinz (Advisor)

Subjects:

Physics, Nuclear

Keywords:

Heavy ion collisions; Hanbury Brown-Twiss interferometry; final state interactions; ultrarelativistic uranium-uranium collisions

Alruwaili, Manal AblukPERFORMANCE OF THE HEAVY FLAVOR TRACKER (HFT) DETECTOR IN STAR EXPERIMENT AT RHIC
MS, Kent State University, 2015, College of Arts and Sciences / Department of Physics
The research field of this work is experimental nuclear physics. I use data taken with the Solenoidal Tracker At RHIC (STAR) experiment at the Relativistic Heavy Ion Collider (RHIC), an accelerator facility located at Brookhaven National Labo- ratory (BNL) in Long Island, NY. RHIC accelerates beams of protons, light and heavy ions (e.g. Au nuclei) to relativistic velocities and collides them. The collisions compress and heat the nuclear matter to very high temperatures and densities, over one trillion degrees Celsius. Under such conditions a phase transition might occur in nuclear matter, a transition, where quarks and gluons become de-confined, i.e. free to move around, forming the so-called Quark Gluon Plasma (QGP). The study of the properties of QGP, its properties and dynamics, provide a deeper understanding of Quantum Chromo-Dynamics (QCD), the theory of strong force, and the conditions in the early universe. A key finding by the experiments at RHIC is the unexpected strong suppression of heavy flavor at high transverse momentum values in Au+Au relative to elementary proton-proton collisions. Heavy quarks are mainly produced during the early stages of the collision when the most energetic interactions occur. The suppression of heavy flavor particles is caused by their interaction with the produced medium, as they tra- verse it. Charm and bottom quark production can be used as a tool to better probe the matter created during the early phases of the collision. The available theoretical models at that time under-predicted the observed suppression. In order to better un- derstand the observed phenomenon and the details of the interaction between heavy flavor quarks and the hot nuclear medium, precision measurements of mesons con- taining charm or bottom quarks needed to be performed by the experiments. Heavy flavor mesons are unstable particles and most of them decay weakly within the first millimeter from the production vertex. Their relative low production rates, low branching ratios (B.R.) to useful channels and short lifetimes (ctau), e.g. D0 -> K¿ + pi (B.R. = 3.89% and ctau = 123µm) makes their reconstruction a challenging task. One needs a very-high precision vertex detector in order to separate the decay products from the thousands of particles produced in the collision. The STAR collab- oration built such a detector, the Heavy Flavor Tracker (HFT) with state-of-the-art silicon pixel technology. The HFT gives us the track pointing precision required to e¿ciently reconstruct charm and bottom meson decay vertices from background. The work in this Thesis is concentrated around the track pointing performance of HFT, sometimes called DCA (Distance of Closest Approach). More specifically we studied the HFT performance using data taken during its first physics run, Run14, that took place in 2014. We present and discuss the details of our analysis methods and the obtained results. We demonstrate that the HFT achieved and exceeded its original design goals in terms of track pointing resolution.

Committee:

Spyridon Margetis (Advisor); Assimoula Katramatou (Committee Member); Declan Keane (Committee Member)

Subjects:

Nuclear Physics; Physics

Keywords:

Nuclear physics, silicon calibration, heavy ion collisions, track pointing, DCA resolution

Danley, Tyler Measurement of Elliptic Flow Coefficients and Derivation of Reaction Plane Dependent Efficiency of Isolated Photons and π0 in Center-of-Mass Pair Energy 200 GeV Au+Au Collisions at RHIC-PHENIX
Master of Science (MS), Ohio University, 2014, Physics and Astronomy (Arts and Sciences)
This thesis presents measurements of second order flow coefficients and derivations of reaction plane dependent efficiencies of isolated photons and π0's in $\sqrt{s_{NN}} = 200\ GeV$ Au+Au collisions at RHIC-PHENIX. We used an isolation cut method similar to those used in direct photon identification where the energy is summed inside an angular cone and cut if greater than a threshold energy. We show that this will result in a reaction plane dependent efficiency. We derive azimuthal single and two particle correlation functions, including this efficiency, up to harmonic second order. These functions were then verified using a Monte Carlo program. Measurements were made in four centralities using the typical event plane method. We show that this method is only sensitive to ν2effective, which includes the sum of true ν2 and the ν2 of the isolation efficiency, which is generally negative. Hence, the measurements of ν2effective are generally smaller, even reaching negative values, than those previously observed for photons and π0's. A method for measuring the efficiency ν2 is presented, which is required in order to find the true isolated photon and π0 ν2.

Committee:

Justin Frantz, Dr. (Advisor); David Drabold, Dr. (Committee Chair); Heather Crawford, Dr. (Committee Member)

Subjects:

Particle Physics; Physics

Keywords:

PHENIX; elliptic flow; RHIC, Heavy Ion Collisions; Gold; flow;

Willson, Robert MichaelThree-Pion HBT Interferometry at the STAR Experiment
Doctor of Philosophy, The Ohio State University, 2002, Physics
During the first year of Au+Au collisions at the Relativistic Heavy-Ion Collider (RHIC) at Brookhaven National Laboratory, 130 A·GeV collisions were observed and analyzed in the hopes of finding some signal of a new state of matter. This new state of matter, the quark-gluon plasma or QGP, can be described as a deconfined state of freely interacting quarks and gluons within a certain volume of the collision fireball. Since the lifetime and size of this state are both small (<10 fm) a direct observation is not possible. Instead, many different indirect methods are used in order to extract specific information about the source from the final state particles which are eventually detected. One of these methods, HBT interferometry, provides a means of determining the spatial extent and dynamical properties of the freeze-out region, after which the final-state particles have stopped interacting, by examining correlations between pairs of particles within an event. Two-particle interactions include those caused by the Coulomb and strong nuclear forces, however it is the quantum statistics governing the behavior of identical particles which leads to a relationship between the spatial properties of the source and the momentum correlations between pairs of particles. In this thesis, one of the central assumptions of HBT interferometry is examined, that of the chaoticity of the freeze-out region. Particles emitted from the freeze-out region carry an intrinsic quantum particle production phase, much like the initial phase of an electromagnetic wave. If these phases are random for each outgoing particle, the source is said to be fully chaotic. Using three-particle HBT interferometry, it is possible to obtain a measure of this chaoticity, and in so doing verify the results of two-particle HBT.

Committee:

Thomas Humanic (Advisor)

Subjects:

Physics, Nuclear

Keywords:

HBT Interferometry; Three Pion Interferometry; Relativistic Heavy Ion Collisions; STAR Experiment; Silicon Vertex Tracker

Wiranata, AntonTransport Coefficients of Interacting Hadrons
Doctor of Philosophy (PhD), Ohio University, 2011, Physics and Astronomy (Arts and Sciences)

A detailed quantitative comparison between the results of shear viscosities from the Chapman-Enskog and Relaxation Time methods is performed for the following test cases with specified elastic differential cross sections between interacting hadrons:

1. The non-relativistic, relativistic and ultra-relativistic hard sphere gas with angle and energy independent differential cross section sigma = a^2/4, where $a$ is the hard sphere radius,

2. The Maxwell gas with sigma (g,Theta)= mGamma(Theta)/2g, where $m$ is the mass of the heat bath particles, Gamma(Theta) is an arbitrary function of Theta, and $g$ is the relative velocity,

3. Chiral pions for which the $t-$averaged cross section sigma = s/(64pi^2 f_pi^4) × (1+1/3 × cos^2 Theta), where $s$ and $t$ are the usual Mandelstam variables and $f_pi$ is the pion-decay constant, and

4. Massive pions for which the differential elastic cross section is taken from experiments.

Quantitative results of the comparative study conducted revealed that

* the extent of agreement (or disagreement) depends very sensitively on the energy dependence of the differential cross sections employed, stressing the need to combine all available experimental knowledge concerning differential cross sections for low mass hadrons and to supplement it with theoretical guidance for the as yet unknown cross sections so that the temperature dependent shear viscosity to entropy ratio can be established for use in viscous hydordynamics.

* The result found for the ultra-relativistic hard sphere gas for which the shear viscosity eta_s = 1.2676~k_BT~c^{-1} /(pi a^2) offers the opportunity to validate ultra-relativistic quantum molecular dynamical (URQMD) codes that employ Green-Kubo techniques.

* shear viscosity receives only small contributions from number changing inelastic processes.

The dependence of the bulk viscosity on the adiabatic speed of sound is studied in depth highlighting why only hadrons in the intermediate relativistic regime contribute the most to the bulk viscosity when only elastic collisions are considered. However, number changing inelastic processes dominate contributions to the bulk viscosity as shown recently by other workers. These combined findings call for developing techniques to include number changing inelastic processes to reliably estimate the magnitude of bulk viscosity in a mixture for temperatures in the range 100 - 200 MeV in which hadrons likely exist during the space-time evolution of a heavy-ion collision.

Illustrative calculations in a binary mixture are performed by varying the mass ratio of the constituents paving the way for future calculations in a multi-component system of hadrons.

An important outcome of this study is that collaborative research to pursue comparative studies with Green-Kubo calculations of viscosities has been initiated with researchers from Duke University.

Committee:

Madappa Prakash, Dr. (Advisor); Charlotte Elster, Dr. (Committee Member); Justin Frantz, Dr. (Committee Member); Alexander Neiman, Dr. (Committee Member); Jeffrey Rack, Dr. (Committee Member)

Subjects:

Physics

Keywords:

Shear Viscosity; bulk Viscosity; Chapman-Enskog Approximation; Relaxation Time Approximation; Relativistic Heavy Ion Collisions

Liu, JiaPre-equilibrium evolution effects on relativistic heavy-ion collision observables
Doctor of Philosophy, The Ohio State University, 2015, Physics
In this thesis, we improve several aspects of the standard model of relativistic heavy-ion collisions. We include a pre-equilibrium dynamical stage and study it in the strong and weak coupling limits. We stress the importance of this stage on the later hydrodynamic evolution as well as on the mean transverse momenta, transverse momentum distributions and anisotropic flow coefficients of directly emitted hadrons. In order to properly address the bulk viscosity, we update the hydrodynamic equations within the boost-invariant viscous hydrodynamic simulation program VISH2+1 to a more complete set of equations that includes non-linear terms related to the shear stress tensor and bulk pressure. The importance of each non-linear term is discussed. With the understanding that the effects of tunable parameters in the heavy-ion simulation model on physical observables are entangled, we optimize them simultaneously. We perform such optimizations for Pb + Pb collisions at the Large Hadron Collider (LHC) for both Monte Carlo Kharzeev-Levin-Nardi (MC-KLN) and Monte Carlo Glauber (MC-Glb) initial-state models. In a first stage we test the parameter optimization routine with zero bulk viscosity and without the hadronic after-burner. This sets the baseline for subsequent searches including the hadronic after-burner and a non-zero bulk viscosity. We report the preferred parameter ranges and compare them across different initial-state models, with and without pre-equilibrium dynamics. The parameter space for the runs with hadronic after-burner is further explored within a Bayesian approach. Using a Markov Chain Monte Carlo routine we determine the posterior probability distribution of each parameter and assign quantitative uncertainty ranges to them.

Committee:

Ulrich Heinz (Advisor); Michael Lisa (Committee Member); Robert Perry (Committee Member); Junko Shigemitsu (Committee Member)

Subjects:

Nuclear Physics; Physics; Theoretical Physics

Keywords:

relativistic heavy-ion collisions; viscous hydrodynamics; specific shear viscosity; specific bulk viscosity

Shen, ChunThe standard model for relativistic heavy-ion collisions and electromagnetic tomography
Doctor of Philosophy, The Ohio State University, 2014, Physics
This thesis focuses on developing a standard theoretical framework to study the bulk dynamics and electromagnetic probes of ultra-relativistic heavy-ion collisions, which are presently studied experimentally at the Relativistic Heavy-Ion Collider (RHIC) and the Large Hadron Collider (LHC). We developed a modular numerical package with different (exchangeable) modular describing different evolution stages of the expanding fireball created in these collisions. For each stage of the collisions, we will give a detailed description of the theoretical model and its corresponding numerical implementation, supplemented with code checking tests. With this framework, we then perform a broad range of phenomenological studies of the bulk dynamics of relativistic heavy-ion collisions from RHIC to LHC energies. Our simulations are compared with various soft hadronic observables, in which the transverse momenta of the hadrons are less than 3 GeV/c. (This includes more than 99% of all particles created in the collision.) These comparisons help us to tightly constrain our theoretical modeling of the fireball evolution and to extract information about the transport properties of the quark-gluon plasma (QGP) as well as about the initial state fluctuation spectrum. We also explore the sensitivity of the hadronic observables to a possible temperature dependence of the QGP specific shear viscosity. The collision energy dependences of hadron spectra and elliptic flow coefficients are studied with our model, providing a qualitative baseline for comparison with recent data from the RHIC Beam Energy Scan (BES) program. Due to the smallness of the electromagnetic coupling compared to the strong interaction, electromagnetic probes in relativistic heavy-ion collisions can provide us with early dynamical evolution information complementary to that obtained from hadronic observables. The emission of direct photons from relativistic heavy-ion collisions is studied. We derive the off-equilibrium corrections to thermal photon emission rates at leading order in O(pi^{mn}/(e + P)), where pi^{mn}, e, and P are the system's shear stress tensor, local energy density, and pressure, respectively. We perform event-by-event simulations for direct as well as hadronic decay photons for relativistic heavy-ion collisions and compare our results with experimental measurements. We map out the space-time structure of thermal photon emission and find that the slope of the measured direct photon spectrum is strongly blue-shifted by the hydrodynamic radial flow. The anisotropic flows of direct photons show a larger sensitivity to the shear pressure tensor of the system than the analogous hadronic observables. This can be used as a sensitive viscometer for the QGP medium created in relativistic heavy-ion collisions.

Committee:

Ulrich Heinz (Advisor); Michael Lisa (Committee Member); Robert Perry (Committee Member); Mohit Randeria (Committee Member)

Subjects:

Nuclear Physics; Physics; Theoretical Physics

Keywords:

relativistic heavy-ion collisions, event-by-event, viscous hydrodynamics, particle spectra, anisotropic flow, specific shear viscosity, Cooper-Frye, thermal photon emission

Taliotis, Anastasios SocratesGeometrical Methods in Heavy Ion Collisions
Doctor of Philosophy, The Ohio State University, 2010, Physics

Currently there exists no known way to construct the Stress-Energy tensor (Tμν) of the medium produced in heavy ion collisions at strong coupling from purely theoretical grounds. In this work, some steps are taken in that direction. In particular, the evolution of Tμν at strong coupling and at high energies is being studied for early proper times (τ). This is achieved in the context of the AdS/CFT duality by constructing the evolution of the dual geometry in an AdS5 background. We consider high energy collisions of two shock waves in AdS5 as a model of ultra-relativistic nucleus-nucleus collisions in the boundary theory. We first calculate the graviton field produced in the collisions in the LO, NLO and NNLO approximations, corresponding to two, three and four-graviton exchanges with the shock waves.

We use this model to study Tμν and in particular the energy density of the strongly-coupled matter created immediately after the collision because as we argue, the expansion of the energy density (ε) in the powers of proper time τ squared corresponds on the gravity side to a perturbative expansion of the metric in graviton exchanges. We point out that shock waves corresponding to physical energy-momentum tensors of the nuclei is likely to completely stop after the collision; on the field theory side, this corresponds to complete nuclear stopping due to strong coupling effects, likely leading to Landau hydrodynamics.

This motivates a more detailed investigation. For this reason we consider the asymmetric limit where the energy density in one shock wave is much higher than in the other one. In the boundary theory this setup corresponds to proton-nucleus collisions. Employing the eikonal approximation we find the exact high energy analytic solution for the metric in AdS5 for the asymmetric collision of two delta-function shock waves. The solution resums all-order graviton exchanges with the nucleus-shock wave and a single-graviton exchange with the proton-shock wave. We show in explicit detail that in the boundary theory the proton is completely stopped by strong-coupling interactions with the nucleus, in agreement with our LO, NLO and NNLO results.

In all the previous calculations, the incident nuclei are assumed to have a constant Tμν on the transverse plane. Improving the earlier works in the literature, we then assume that the two nuclei have a non-trivial transverse profile and collide wit an impact parameter b. The nuclear matter is modeled by two shock waves corresponding to a non-zero five dimensional bulk Stress-Energy Tensor JMN. An analytic formula for Tμν at small τ is derived and is used in order to calculate the energy density, the momentum anisotropy and the spatial eccentricity of the medium produced in the collision. The results agree qualitatively with the results obtained in the context of perturbation theory and by using hydrodynamic simulations.

Committee:

Yuri Kovchegov (Advisor); Richard Furnstahl (Committee Member); Eric Braaten (Committee Member); Michael Lisa (Committee Member); Wang DeLiang (Other)

Subjects:

Physics

Keywords:

Heavy Ion Collisions; AdS/CFT Correspondence; Stress Energy Tensor; Nuclear Stopping; Transverse Dynamics; Eccentricity.

Willson, Robert Michael.Three-pion HBT interferometry at the STAR experiment /
Doctor of Philosophy, The Ohio State University, 2002, Graduate School

Committee:

Not Provided (Other)

Subjects:

Physics

Keywords:

Interferometry;Heavy ion collisions

Lomnitz, Michael RichardMeasurement of charmed meson azimuthal anisotropy in Au+Au collisions at a center of mass energy of 200 GeV per nucleon pair at RHIC
PHD, Kent State University, 2016, College of Arts and Sciences / Department of Physics
Heavy ion collisions at RHIC provide a unique environment to probe into the understanding of nuclear matter under extreme high temperature and density conditions. Among the many insights that can be provided is the further understanding of the QCD (Quantum Chromo Dynamics) phase diagram and equation of state, as well as search for evidence of the QCD critical point and chiral symmetry restoration. Production of heavy quarks in high-energy nuclear collisions at RHIC occurs mainly through gluon fusion and quark anti-quark annihilation; and while heavy flavor production may be somewhat enhanced due to final state interactions via thermal processes these channels are greatly suppressed due to the heavy quark masses. Thus heavy flavor provides an ideal probe in the study of the hot and dense medium created in high-energy collisions as it is produced early in the evolution of the collision, and hence is sensitive to the collision dynamics of the partonic matter at early stages. Previous measurements of collective motion (flow) in light quarks (u,d,s) at RHIC suggest that partonic collectivity has been achieved in the collisions. These results also seem to suggest that the dense matter produced during collisions thermalizes at very high temperatures and form a strongly coupled Quark Gluon Plasma (QGP) whose behavior is compatible with viscous hydrodynamic models with a low shear-viscosity-to-entropy-density (η/s) ratio. The question remains as to whether or not this collective behavior applies to heavy flavor and a detailed description of the behavior of heavy flavor is essential to understand the underlying dynamics, distinguish between different energy loss mechanisms, and constrain theoretical models. In particular, if the elliptic flow of charm quarks is found to be comparable to that of lighter matter this would be indicative of frequent interactions between all quarks and would strongly support the discovery of QGP at RHIC. Understanding how this collective behavior emerges from the individual interactions between partonic matter as well as the differences between quarks species will need to be investigated further to understand this new state of matter and is at the center of the RHIC scientific program. However, precise measurements of open heavy flavor are difficult to obtain due to the low yields and short lifespan of heavy hadrons. One approach to reduce this combinatorial background and reconstruct open heavy flavor in heavy ion collisions involves distinguishing between an event's primary vertex and a hadron's decay vertex through direct topological reconstruction from the decay products. The Heavy Flavor Tracker (HFT) silicon vertex upgrade for the STAR experiment, which made its debut during the 2014 year's run together with the Muon Telescope Detector (MTD), has vastly improved the experiment's heavy flavor capabilities making STAR an ideal detector to study the hot and dense matter created in heavy ion collisions. Taking advantage of the greatly improved pointing resolution from a dedicated micro-vertex detector, it is possible to directly track and reconstruct weak decay products from hadrons comprised of heavy ``charm" and ``bottom" quarks. The HFT consists of three sub-detectors: PIXEL (PXL), the Intermediate Silicon Tracker (IST) and the Silicon Strip Detector (SSD) with 4 separate layers of silicon to guide tracks reconstructed in the Time Projection Chamber down to a pointing resolution of around 30 \mum for one GeV/c pions, a requirement to distinguish between an event's primary vertex and the position of a hadron's decay. This dissertation is centered on using the HFT to reconstruct charmed mesons in Au+Au collisions at a center of mass energy of 200 GeV per nucleon through their hadronic channels (D+/-→K-/+2π+/-, D0→K-π+). In order to achieve the precision of the HFT for physics analysis, careful calibration of the detector is essential to ensure the quality of the processed data and, as a consequence, any measured observables. As such, details related to the identification of bad channels in the PXL subsystem as well as the internal alignment of the HFT detector are presented in this dissertation. In-depth studies of the detector's response were performed in simulations and, together with comparisons to data, were used to verify our understanding of the detector's delivered efficiency and tracking performance. As motivated above, a sizable sample of charmed meson candidates was obtained and used to study the flow patterns employing the event plane method, whose simple interpretation allows for immediate comparison to theoretical models. The thesis presents the first measurement of D-meson v2 and v3 at RHIC energy, and the result shows D-meson v2 is finite indicating charm quarks are participating the collective behavior with the medium. The results are compared to lighter particle species and appear to follow the same Number of Constituent Quarks (NCQ) scaling as is observed for other hadrons. The measured v3 is found to be non-zero within large uncertainties, indicating the importance of considering fluctuations in the initial conditions of the collision. These results are then compared to a series of model calculations in an attempt to extract information related to the transport properties of the bulk matter formed in the collision. In particular, the measured elliptic flow for D0 is found to favor a scenario where charm quarks flow with the medium and compatible with a (3+1)D viscous hydrodynamics. The comparisons were used to extract a range of compatible values for the charm spatial diffusion coefficient 2πTDs in the QGP medium. Once processed, the dataset collected in 2016 (~2 billion MinBias events) will provide a further factor 2-4 in the D0 significance. This dataset will allow STAR to study the centrality dependence of charm hadron v2 in more detail as well as the production of open bottom at RHIC in order to further constrain the transport properties of the medium.

Committee:

Margetis Spyridon, Prof. (Advisor); Xin Dong, Dr. (Advisor)

Subjects:

Nuclear Physics; Physics

Keywords:

Nuclear Physics; Heavy Ion Collisions; Quark Gluon Plasma; Heavy Flavor; RHIC

López Noriega, MercedesPion interferometry in AuAu collisions at a center of mass energy per nucleon of 200 GeV
Doctor of Philosophy, The Ohio State University, 2004, Physics

Quantum Chromodynamics predicts a phase transition from a state formed by hadrons to a plasma of deconfined quarks and gluons, the Quark Gluon Plasma, as a the energy density exceeds a critical value. This deconfined phase is believed to be the one in which the early universe existed in a time-scale ∼ 10-5 s after the Big Bang.

Ultrarelativistic Heavy Ion Collisions, like the ones that take place at the Relativistic Heavy Ion Collider at Brookhaven National Laboratory, reach energy densities above the critical value creating a deconfined phase of quarks and gluons that can be studied at the laboratory. This gives us the opportunity to study a phase of matter in the deconfined region of QCD, the properties of the strong interaction, the formation of hadronic matter and the interaction between hadrons.

In the analysis presented in this thesis, the dynamical evolution of the particle emitting source and its space-time structure at freeze-out is studied using the two particle intensity interferometry technique. The expansion of the source is also studied. We find indications that this expansion may be caused by the initial pressure gradient generated in the initial stages of the collision through particle rescattering in a very dense medium.

Committee:

Michael Lisa (Advisor)

Subjects:

Physics, Nuclear

Keywords:

Relativistic Heavy Ion Collisions; Two particle intensity interferometry; Pion intensity interferometry; HBT; STAR; RHIC