Search Results (1 - 19 of 19 Results)

Sort By  
Sort Dir
 
Results per page  

Subedi, Ramesh RajStudying Short-Range Correlations with the 12C(e,e'pn) Reaction
PHD, Kent State University, 2007, College of Arts and Sciences / Department of Physics
We investigated electron-induced two-nucleon emission from carbon with the goal of being sensitive to and studying short-range correlations using the 12C(e,e'pN) reaction in a triple-coincidence measurement. Two existing high-resolution spectrometers in Hall A at Jefferson Laboratory were used to detect coincident scattered electrons and struck nucleons. A large neutron detector designed and constructed specially for this experiment was used to detect the recoiling neutrons. We performed analysis of the 12C(e,e'pn) reaction, and made direct observation of short-range correlated n-p pairs. From our analysis we conclude that there are 17.9 ± 4.5 times more n-p short-range correlated pairs than p-p short-range correlated pairs.

Committee:

John Watson (Committee Co-Chair); Douglas Higinbotham (Committee Co-Chair); Byron Anderson (Other); George Fai (Other); Christopher Woolverton (Other)

Subjects:

Physics, Nuclear

Keywords:

Neutron; Neutron Detector; Scintillator; BigBite; Detector; Momentum

Ramanan, SunethraInvestigations of the renormalization group approach to the nucleon-nucleon interaction
Doctor of Philosophy, The Ohio State University, 2007, Physics
This thesis work has investigated the Renormalization Group theory for the nucleon-nucleon interaction. Conventional nuclear many-body calculations have the following sources of non-perturbative physics: 1. a strongly repulsive short-range interaction, 2. a tensor force, e.g. from pion exchange, which is highly singular at short-distances, 3. the presence of low-energy bound states or nearly bound states (in the S waves). The RG approach exploits the insensitivity of low-energy processes to the details of the high-energy physics. Using any of the high-precision potentials as input, the high-momentum intermediate states in the Lippmann-Schwinger equation for the T matrix in a particular partial-wave are cut-off at lambda. The details of the physics beyond this limit of resolution are integrated out and included in the potential by requiring that the half-off shell T matrix elements be independent of the cut-off lambda. This requirement leads to a low-momentum potential Vlowk, which is energy independent. The choice of the regulator which cuts off the high momentum intermediate states is investigated. Sharp cut-offs, though straight forward, lead to convergence issues in few-body calculations that are eliminated using smooth regulators. The construction of low-momentum potentials using a smooth regulator is explored in detail. In the course of this study, a three-step process to calculate Vlowk requiring the cut-off independence of the fully-off shell T matrix elements has been established and this yields better numerical stability than the energy-independent RG. The complex eigenvalues (Weinberg eigenvalues) of the operator G0(z)V, which appears in the Lippmann-Schwinger equation, are a useful tool for investigating the convergence of the Born series. Weinberg eigenvalues for Vlowk potentials, including chiral effective theory potentials, have been investigated as a function of cut-off. The studies reveal the density and/or scale dependence of the sources of non-perturbative physics. The in-medium eigenvalues near the Fermi surface give a good estimate of the pairing gaps. Using two-particle Nambu-Gorkov propagators, the eigenvalue equation at Fermi energy is the gap equation and the eigenvectors corresponding to the largest eigenvalue gives the first approximation to the gap function Delta(k), which can be further iterated using the BCS gap equation to give self-consistent gaps.

Committee:

Richard Furnstahl (Advisor)

Subjects:

Physics, Nuclear

Keywords:

nuclear physics,; effective field theory

Bhattacharyya, AnirbanApplication of effective field theory to density functional theory for finite systems
Doctor of Philosophy, The Ohio State University, 2005, Physics
Density functional theory (DFT) is a tool of many-body physics whose popularity has grown over the years, primarily because it provides a useful balance between accuracy and computational cost, allowing large systems to be treated in a simple self-consistent manner. Effective field theory (EFT) is a framework which allows us to study the low-energy phenomena of a system in a systematic fashion. In this thesis, EFT methods are applied to DFT as part of a program to systematically go beyond mean-field approaches to medium and heavy nuclei. A system of fermions with short-range, natural interactions and an external confining potential (e.g., fermionic atoms in an optical trap) serves as a laboratory for studying DFT/EFT. An effective action formalism leads to a Kohn-Sham DFT by applying an inversion method order-by-order in the EFT expansion parameter. Results showing the convergence of Kohn-Sham calculations at zero temperature in the local density approximation (LDA) are compared to Thomas-Fermi calculations and to power-counting estimates. When conventional Kohn-Sham DFT for Coulomb systems is extended beyond the local density approximation, the kinetic energy density is sometimes included in energy functionals in addition to the fermion density. However, a local (semi-classical) expansion of the kinetic energy density is used to write the energy as a functional of the density alone, in contrast to the Skyrme approach. The difference is manifested in different single-particle equations, which in the Skyrme case include a spatially varying effective mass. The EFT framework for DFT is generalized to reconcile these approaches. An effective action approach is used to illustrate how the exact Green's function can be calculated in terms of the Kohn-Sham Green's function. An example based on Skyrme energy functionals shows that single-particle Kohn-Sham spectra can be improved by adding sources used to construct the energy functional. Finally, spin-orbit interactions are incorporated in the formalism leading to an energy functional having the same form as that of the Skyrme functional. Gradient expansions in terms of the local Fermi momentum are also worked out, which will be of use in the immediate future.

Committee:

R. Furnstahl (Advisor)

Subjects:

Physics, Nuclear

Keywords:

Density functional theory; Effective field theory; Effective action; Skyrme functional; Kohn-Sham theory; Semi-classical expansion

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

Bade, Christopher MRF Methods to Increase Deuteron Polarization in HD Targets and NMR Spin-Polarization Analysis at LEGS
Doctor of Philosophy (PhD), Ohio University, 2006, Physics (Arts and Sciences)
Double-polarization π-photoproduction experiments have been conducted at the laser electron gamma source Compton back-scattering facility at Brookhaven National Laboratory. Experiments have been conducted on frozen-spin molecular hydrogen deuteride targets using both polarized proton and polarized deuteron targets. The Strongly Polarized Hydrogen Ice target system was used in these experiments. The targets are polarized in a 3He/4He dilution refrigerator at a temperature of 12 mK and a magnetic field of B = 15 T and aged for a number of months. The target’s polarization is measured after aging the target to calculate the polarization of the target during the experiment. The run is conducted in-beam at B = 0.9 T at a temperature of 0.3 K in a cryostat designed with minimal materials in the path of nuclear reaction products. Methods to boost polarization of the target are discussed. The radio frequency transfer of nuclear polarization from H to D by saturating the forbidden H - D resonance is described and results are presented. Forbidden saturation is shown to be more useful and less problematic than forbidden passage with the available target system and equipment. The method for determining polarization from NMR data is described. Additional work would be required to reduce uncertainty in the polarization measurements. Some preliminary results for the D(γ,π0n) reaction which demonstrate the quality of the polarized deuteron target are presented

Committee:

Kenneth Hicks (Advisor)

Subjects:

Physics, Nuclear

Keywords:

Hydrogen Deuteride; Frozen-spin; Spin-polarization; NMR; Pi Photoproduction; Solid Target

Pidopryhora, YuriiTesting the Low Energy Theorem for Spinless “Proton-Neutron” Bremsstrahlung
Master of Science (MS), Ohio University, 2003, Physics (Arts and Sciences)

In this thesis the accuracy of using the Low energy theorem(soft-photon pproximation) to estimate the amplitude for spinless “proton-neutron” bremsstrahlung is investigated. For this purpose spinless elastic scattering and bremsstrahlung theories are constructed. An exact expression for the bremsstrahlung amplitude is derived and an original proof of the Low energy theorem is given in this case. Computations are performed which compare the exact value of the bremsstrahlung amplitude to the Low energy theorem's approximation thereof in different scattering configurations. We find that in most of the cases considered the Low energy theorem is a good estimate for the “exact” spinless “proton-neutron” bremsstrahlung amplitude. This result may be used to justify Low energy theorem estimates of cross-sections for neutrinostrahlung processes, relevant in astrophysics. Detailed explanations are given so that this text may be used as a reference by students and teachers of nuclear physics and quantum mechanics.

Committee:

Daniel Phillips (Advisor)

Subjects:

Physics, Nuclear

Keywords:

Few-Body Nuclear Theory; Neutron Star Cooling; Bremsstrahlung; Soft-Photon Approximation; Modified URca Process; Proton-Neutron scattering

Jarecke, Dennis WProperties of Mesons From Bethe-Salpeter Amplitudes
PHD, Kent State University, 2005, College of Arts and Sciences / Department of Physics
The vector meson strong decays ρ→ππ φ→KK, and K*→πK are studied within the covariant, nonperturbative, rainbow-ladder truncation of the Dyson-Schwinger equations in Quantum Chromodynamics. The model gluon propagator has gluon confinement, preserves the one-loop perturbative behavior of QCD, and contains an infrared enhancement for the dynamical generation of large constituent quark mass. The quark propagators are confined and produce a non-zero quark condensate in the chiral limit signaling dynamical chiral symmetry breaking. The analytic continuation of the Dyson-Schwinger equations are also studied. An expedient approach is used which modifies the gluon propagator in a physically insignificant way but allows for contour integration along the positive real-axis. Singularities are found that limit the Taylor expansion of quark propagators. We employ a Taylor expansion of the quark propagators and compare the resulting light scalar and vector meson masses and electroweak decay constants with solutions of the Bethe-Salpeter equation resulting from direct analytic continuation of the quark propagators. Our results show a convergence at second order in the Taylor expansion of the quark propagators and provides meson masses and electroweak decay constants within a few percent of experimental results. The 3-point decay amplitudes are studied in the impulse approximation providing vector meson strong decays within 15% of experimental results. We study a real-axis projection of the complex plane behavior of the quark propagators to obtain axial-vector and exotic meson masses 400 MeV too low.

Committee:

Peter Tandy (Advisor)

Subjects:

Physics, Nuclear

Keywords:

quark; Dyson-Schwinger; Bethe-Salpeter; meson; strong decays

Bekele, SelemonNeutral kaon correlations in Au-Au collisions at center of mass energy of 200 GeV per nucleon pair
Doctor of Philosophy, The Ohio State University, 2004, Physics
A few microseconds after the Big Bang, the universe is believed to have existed in the form of a plasma composed of strongly interacting particles known as quarks and gluons. Although the quarks and gluons behave as asymptotically free particles in a Quark Gluon Plasma (QGP), free quarks and gluons have never been discovered in the laboratory. Experiments at the Relativistic Heavy Ion Collider (RHIC) aim to create conditions similar to the early universe by colliding heavy ions at the highest energies possible in the hope of observing a phase transition from a QGP into hadronic degrees of freedom. The response of the space time structure of the hot reaction zone created in a heavy ion collision to a phase transition is one of the many observables being studied at RHIC. Making use of the techniques of two particle intensity interferometry, also known as the HBT effect, the RHIC experiments are studying the space-time structure and dynamical properties of the region from which particles are emitted. A large spatial size and long duration of particle emission are the predicted signals for a phase transition from a QGP to a hadronic phase. In this thesis we present results on the first measurement of one dimensional K0s K0s interferometry by the STAR experiment at RHIC in central (small impact parameter) Au-Au collisions at center of mass energy of 200 GeV per nucleon pair. The λ parameter, which is a measure of the sources chaoticity, is found to be consistent with unity confirming the fact that the source is mostly chaotic as measured by STAR using three particle correlations. Without taking into account the effect of the strong interaction, the invariant radius Rinv is found to be large for the mean transverse mass Mt of the pair, which is about 980 MeV/c, compared to expectations from charged pion correlations at the same Mt . Including the effect of the strong interactions makes the radius parameter for the K0s K0s system fall within the charged pion Mt systematics. Our result serves as a valuable cross-check of charged pion measurements which are mainly affected by contributions from resonance decays and final state interactions. This is also an important first step towards a full three dimensional analysis of neutral kaon correlations as high statistics data from RHIC will be available in the near future.

Committee:

Thomas Humanic (Advisor)

Subjects:

Physics, Nuclear

Keywords:

HBT interferometry; Neutral kaons

Mohr, Richard FrankQuantum mechanical three-body problem with short-range interactions
Doctor of Philosophy, The Ohio State University, 2003, Physics
We have investigated S-wave bound states composed of three identical bosons interacting via regulated delta function potentials in non-relativistic quantum mechanics. For low-energy systems, these short-range potentials serve as an approximation to the underlying physics, leading to an effective field theory. A method for perturbatively expanding the three-body bound-state equation in inverse powers of the cutoff is developed. This allows us to extract some analytical results concerning the behavior of the system. Further results are obtained by solving the leading order equations numerically to 11 or 12 digits of accuracy. The limit-cycle behavior of the required three-body contact interaction is computed, and the cutoff-independence of bound-state energies is shown. By studying the relationship between the two- and three-body binding energies, we obtain a high accuracy numerical calculation of Efimov's universal function. Equations for the first order corrections, necessary for the study of cutoff dependence, are derived. However, a numerical solution of these equations is not attempted.

Committee:

Robert Perry (Advisor)

Subjects:

Physics, Nuclear

Keywords:

quantum mechanics; three-body problem; delta function potential; Efimov function; uniform expansion

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

Ayieta, Elijah Omoloeffects Of Absorbers on Perturbed Angular Correlation Spectrum
Master of Science, Miami University, 2004, Physics
The aim of this thesis is to study effects of absorbers on perturbed angular correlation spectrum and present the results as well. This thesis will provide a reference to future work on perturbed angular correlation spectrum. A hafnium sample made radioactive by neutron irradiation has been used in this research and it is my hope that it will provide a good reference for future work. The results showed that there is a sizeable effects on angular correlation spectrum when a material is placed between the sample and the source. However, the electric field gradient parameters are not affected by the absorbers. The A2 values decreased with increasing thickness of the absorber and with an off-set absorber position. A2 also decreases with increasing width of the single channel windows.

Committee:

Herbert Jaeger (Advisor)

Subjects:

Physics, Nuclear

Choudhury, DeepshikhaInvestigating Neutron Polarizabilities and NN Scattering in Heavy-Baryon Chiral Perturbation Theory
Doctor of Philosophy (PhD), Ohio University, 2006, Physics (Arts and Sciences)

Understanding nucleon structure is one of the prime objectives of contemporary Nuclear Physics. This dissertation examines neutron electromagnetic structure, specifically the neutron polarizabilities, through Compton scattering on the deuteron and 3He. Experiments and theory in the past decade or so have improved our understanding of proton polarizabilities, but those of the neutron still remain “elusive”. In this thesis, we report the first calculations for γ3He scattering. We also report the first calculations in Chiral Perturbation Theory for polarized γd scattering.

Our calculations for elastic γd scattering show that the beam asymmetry, Σ is not a good observable to extract the spin-independent polarizabilities, αn or βn, and that the double-polarization observable, Δx, is sensitive to a linear combination of two of the neutron spin polarizabilities, γ1n and γ3n. Including the Δ-isobar explicitly in our calculations enhances the sensitivity of Δx to γ1n and γ3n and also identifies Δz as a possible observable to measure a linear combination of γ1n, γ2n, and γ4n at forward angles.

Our results for elastic γ3He scattering are quite encouraging for the extraction of neutron polarizabilities. The unpolarized dcs can be used to measure αn and βn. Meanwhile, Δz and Δx are sensitive to two different linear combinations of the neutron spin polarizabilities, γ1n, γ2n, and γ4n. Taken in concert with our γd results, this suggests that a combination of experiments and further theoretical efforts will provide an extraction of the neutron polarizabilities.

Since this project involves nuclear targets, we also model the NN interaction in the 1S 0 channel to better comprehend the forces that hold nuclei together. We investigate whether a perturbation expansion can be built for at least a part of the interaction. We have been successful in building such an expansion where we regulate the strong short-range pieces by a ‘slanty’ well with finite range (>1.5 fm) and treat the weak longer-range pieces perturbatively.

Committee:

Daniel Phillips (Advisor)

Subjects:

Physics, Nuclear

Keywords:

Polarizability; Compton Scattering

Matei, CatalinNucleosynthesis of 16O Under Quiescent Helium Burning
Doctor of Philosophy (PhD), Ohio University, 2006, Physics (Arts and Sciences)

The 12C(alpha,gamma) 16O radiative capture reaction is one of the most important reactions in nuclear astrophysics as its reaction rate determines the C/O ratio in the Universe. A better understanding of this reaction is what motivates the experiments presented in this thesis.

In experiments performed at Ohio University angular distributions and branching ratios of the 7.12- and 6.92-MeV transitions in 16O were measured. An upper limit was set on the 7.12 to 6.13-MeV transition in 16O. These results will better constrain the alpha-reduced width of the 6.92-MeV state in 16O which is important for the extrapolation to helium-burning energies of both the E2 transition and cascade through the 6.92-MeV state.

At the DRAGON recoil separator at TRIUMF, Canada, the E to 6.05 MeV transition in 12C(alpha,gamma) 16O was measured over a wide range of energies. The result shows that the cascade through the 6.05-MeV state is the most important cascade in 12C(alpha,gamma) 16O with an extrapolated S-factor at 300 keV, S 6.05(300)=25±16 keV b. A new value for the total S-factor at 300 keV is proposed.

Committee:

Carl Brune (Advisor)

Subjects:

Physics, Nuclear

Keywords:

branching ratios in 16O; cascade transitions in 16O; the 6.05-MeV state in 16O

Mozer, Matthias U.Transferred Polarization in Σ0 Electroproduction
Master of Science (MS), Ohio University, 2002, Physics (Arts and Sciences)
In this work Σ0 electroproduction via the ep → e′K+Σ0 reaction is investigated. In particular the polarization of the Σ0 that is transferred from the incoming polarized electron beam is measured. The data was obtained in the 1999 E1C running period at the Thomas Jefferson National Accelerator Facility at a beam energy of 2.567 GeV, and covers a wide kinematic range. The polarization can be extracted from the distribution of the decay proton of the daughter Λ that is the result of the Σ0 decay. The polarization was found along three different sets of coordinate axes and the dependence of the polarization on different kinematic variables was investigated. The polarization is in general quite large, but with large statistical uncertainties. The values obtained for the polarization are then compared to the predictions of several hadrodynamic models and conclusions about the validity of these models and the intermediate states included in them are drawn.

Committee:

Daniel Carman (Advisor)

Subjects:

Physics, Nuclear

Keywords:

Sigma; Polarization; Electroproduction

Weisberg, AdamA Preliminary Cross Section Measurement for K0∗Σ+ Electroproduction
Master of Science (MS), Ohio University, 2001, Physics (Arts and Sciences)

We study data acquired at the Thomas Jefferson National Accelerator Facility to obtain cross sections for the reaction:

e+p→e′+K0∗(892)+Σ+(1189),

measuring cross sections at a beam energy of 4.2 GeV of a few hunderd nb, depending on the available energy in the reaction. A second measurement is made, strictly as a consistency check, which about half as much data taken at a beam energy of 4.4 GeV.

The particles detected in the final state include the scattered electron, and the K0∗ decay products, K+ and π. Our statistical error is on the order of 15%.

This represents the first-ever measurement of this final state with an electron beam. These data are expected to be an important test of theoretical models of the process.

Committee:

Kenneth Hicks (Advisor)

Subjects:

Physics, Nuclear

Keywords:

kaon; strange; CEBAF; sigma;

Wells, Randall CAzimuthal Dependence of Pion Interferometry in Au+Au Collisions at a Center of Mass Energy of 130AGeV
Doctor of Philosophy, The Ohio State University, 2002, Physics

The study of two-pion Bose-Einstein correlations provides a tool to extract both spatial and dynamic information regarding the freeze-out configuration of the emission region created in heavy ion collisions. Noncentral heavy ion collisions are inherently spatially and dynamically anisotropic. The study of such collisions through the φ dependence of the HBT radii, Rij2 , relative to the event plane allows one to observe the source from all angles, leading to a richer description of the interplay between geometry and dynamics.

The initial heavy ion running of the Relativistic Heavy Ion Collider (RHIC) at Brookhaven National Laboratory provided Au + Au collisions at 130GeV. The focus of the heavy ion program at RHIC is the search for a new state of strongly interacting matter, the quark gluon plasma (QGP). STAR is a large acceptance detector at RHIC with azimuthal symmetry, allowing the study of a large variety of observables on an event-by-event basis to provide a better characterization of the freeze-out conditions. The detector geometry for the first year’s data consisted of a time projection chamber (TPC) immersed in a 0.25T magnetic field oriented along the symmetry axis to provide identification of particles with transverse momenta pT ≥100MeV/c.

The focus of this dissertation is the study of the φ dependence of the transverse HBT radii from ππ and π+π+ correlations in non-central collisions. 2nd order oscillations are observed in all transverse radii (Ro2 (φ), Rs2 (φ), and Ros2 (φ)). The oscillations are found to be consistent in phase and magnitude to both RQMD and hydrodynamic predictions, yet both models (over)underpredict (Ro2)Rs2 whose relative size indicates a short emission time-scale. A modified blast wave prameterization is successful at reproducing a variety of observables at RHIC (i.e. particle spectra, v2 (pT), Rij2 (pT), and Ro,s,os2 (φ)) with a univeral set of freeze-out parmeters. The results describe a freeze-out geometry extended out-of-plane indicative of a short source life-time.

Committee:

Michael Lisa (Advisor)

Subjects:

Physics, Nuclear

Keywords:

Nuclear Physics; Azimuthal Pion Interferometry; Relativistic Heavy Ion Physics

Wang, GangCORRELATIONS RELATIVE TO THE REACTION PLANE AT THE RELATIVISTIC HEAVY ION COLLIDER BASED ON TRANSVERSE DEFLECTION OF SPECTATOR NEUTRONS
PHD, Kent State University, 2006, College of Arts and Sciences / Department of Physics
Modern physics is challenged by the puzzle of quark confinement in a strongly interacting system. High-energy heavy-ion collisions can experimentally provide the high energy density required to generate Quark-Gluon Plasma (QGP), a deconfined state of quark matter. For this purpose, the Relativistic Heavy Ion Collider (RHIC) at Brookhaven National Laboratory has been constructed and is currently taking data. Anisotropic flow, an anisotropy of the azimuthal distribution of particles with respect to the reaction plane, sheds light on the early partonic system and is not distorted by the post-partonic stages of the collision. Non-flow effects (azimuthal correlations not related to the reaction plane orientation) are difficult to remove from the analysis, and can lead us astray from the true interpretation of anisotropic flow. To reduce the sensitivity of our analysis to non-flow effects, we aim to reconstruct the reaction plane from the sideward deflection of spectator neutrons detected by the Zero Degree Calorimeter (ZDC). It can be shown that the large rapidity gap between the spectator neutrons used to establish the reaction plane and the rapidity region of physics interest eliminates all of the known sources of non-flow correlations. In this project, we upgrade the ZDC to make it position-sensitive in the transverse plane, and utilize the spatial distribution of neutral fragments of the incident beams to determine the reaction plane. The 2004 and 2005 runs of RHIC have provided sufficient statistics to carry out a systematic analysis of azimuthal anisotropies as a function of observables like collision system (Au+Au and Cu+Cu), beam energy (62 GeV and 200GeV), impact parameter (centrality), particle type, etc. Directed flow is quantified by the first harmonic (v1) in the Fourier expansion of the particle’s azimuthal distribution with respect to the reaction plane, and elliptic flow, by the second harmonic (v2). They carry information on the very early stages of the collision. For example, the variation of directed flow with rapidity in the central rapidity region is of special interest because it might reveal a signature of a possible QGP phase. This flow study using the 1st-order reaction plane (the reaction plane determined by directed flow) reconstructed using the ZDC-SMD has minimal, if any, influence from non-flow effects or effects from flow fluctuations. The experimental results can be compared with different theoretical model predictions such as AMPT, RQMD, UrQMD and hydrodynamic models. We can also use our flow results to test the hypothesis of limiting fragmentation - the effect whereby particle emission as a function of rapidity in the vicinity of beam rapidity appears unchanged over a wide range of beam energy.

Committee:

Declan Keane (Advisor)

Subjects:

Physics, Nuclear

Keywords:

RHIC; STAR; Anisotrpic flow; ZDC-SMD

Mironov, CameliaCharged Kaon Production in p+p and d+Au Collisions, the Baseline Comparison Systems for Understanding Au+Au Collisions at RHIC
PHD, Kent State University, 2005, College of Arts and Sciences / Department of Physics

One of the primary challenges in modern nuclear physics is to understand the properties of hot nuclear matter. The expectation is that at sufficiently high energy densities, nuclear matter undergoes a phase transition where individual nucleons ‘dissolve’ and a plasma of freely moving quarks and gluons is formed. To accomplish this in the laboratory, normal nuclear matter is heated and compressed through collisions of heavy nuclei at relativistic energies.

The Relativistic Heavy Ion Collider (RHIC) at Brookhaven National Laboratory is a dedicated particle accelerator, capable of colliding nuclear beams to energies up to 100 GeV per nucleon per beam. Particle species ranging from protons (A=1) to gold (A=197) are accelerated in this state-of-the-art facility and collide at selected intersection points.

In this dissertation, a detailed transverse momentum (pT) analysis is made at central rapidities, using the STAR Time Projection Chamber (TPC). The data set is comprised of about 10 million d+Au and about 6 million p+p events at 200 GeV. Previously analyzed data from a 2002 Au+Au run are also used. This work concentrates on the study of identified charged kaons (K+, K-), which are the lightest strange mesons and hence the particles that dominate strangeness production. Charged kaons are identified using a topological reconstruction method which has relatively large pT coverage.

In this dissertation, we present pT and yield systematics. We find that the particle to anti-particle ratio is pT independent in all colliding systems studied, an indication that in the pT range studied, the pQCD regime is not reached yet. The ratios, close to unity, signal a rather net-baryon-free mid-rapidity region. The <pT> in central d+Au collisions is larger than in peripheral Au+Au collisions, which might hint at the presence of ‘Cronin effect’ in the dAu system as explained.

We also obtain results on nuclear modification factors (RdACP - central to peripheral ratio, RdA, RAA - geometrically scaled Au+Au(d+Au) to p+p ratios) which are presented for various mesons and baryons. In d+Au collisions, an enhancement compared to binary scaling of both RdACP and RdA is observed, an experimental observation called ‘Cronin effect’. This result is thought to be an initial-state effect. In contrast, the same ratio in central Au+Au collisions exhibits a suppression instead of an enhancement. This was understood in terms of a dense partonic medium which induces energy loss via gluon radiation by a high-energy parton traversing the medium, and leads, after fragmentation, to hadrons with lower <p T >. The meson-baryon differences, first observed in Au+Au RAACP, also exist in d+Au collisions.

Committee:

Spyridon Margetis (Advisor)

Subjects:

Physics, Nuclear

Keywords:

AU; KAON; GeV; hadrons; COLLISIONS; 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