Abstract Not Available.

After a brief introduction describing some of the physics and mechanics of scintillation detection, results of the development for the Central Trigger Barrel (CTB) for STAR and the Start Counter for CLAS are discussed. For the CTB development, 1 cm x 20 cm x 100 cm scintillators were studied with light guides of various geometries and materials attached to one end in order to optimize the uniformity and overall gain. The best results were obtained using a 61$\sp\circ$ OP-1 light guide attached to a BC 408 scintillator. An alternate approach using a wavelength shifter produces much lower pulse heights than the other method. The CEBAF scintillators are intended to enclose the target area in order to identify the beam bucket for a particular event with timing resolution of 350 ps or less. Single paddle and coupled-paddle approaches are discussed. The coupled-paddle approach meets the design goals.

We construct a quark-soliton model of the nucleon which interpolates between the MIT bag model of arbitrarily confined relativistic quarks and the Skyrme model in which the nucleon is a topological knot in the pion field. Confinement is achieved using the color dielectric model. The field equations are solved numerically for the so called hedgehog state for which the field equations reduce to radial ones. Nucleon observables are calculated by projecting the quark-soliton hedgehog ground state onto spin-isospin eigenstates, which are taken to be variationally best nucleon and nucleon isobar states.

The Exit Charge Detector (ECD) is used to determine the impact parameter of relativistic gold-gold interactions in BNL-AGS Experiment 896 by measuring the total charge of projectile-like particles in each collision. Results are presented from simulations which optimized the ECD's dimensions. The ECD was then constructed, and the hardware and the construction techniques used are described. Analyses of data from the operation of the ECD in heavy-ion collisions are discussed. These analyses indicated a significant amount of correlated noise in the experiment. A method to correct for this noise offline is discussed. Also, significant probabilities for the interaction of the beam with materials other than the target are investigated. Finally, plans to improve the detector for the coming Spring 1998 $\rm\sp{197}Au$ run are discussed.

The quark wave-functions of the lower-lying excited-state hyperons Λ(1405), Λ(1385), and Λ(1520) are not well understood. For example, the Λ(1405) may not be a regular three-quark state but K¯N molecule. Several competing models have been proposed, but none have been convincingly eliminated. Measuring radiative decays provides a means of discriminating between the models. The radiative branching ratios are predicted to be small (∼1%), but the radiative widths vary by factors of 2--10 from model to model. The existing experimental data is sparse and inconsistent; moreover, the radiative decay of the Sigma(1385) has never been observed before (except for one event). These lower-lying excited-state hyperons were produced in a tagged photon-beam experiment in the CLAS detector at TJNAF in the reaction gammap → K+Y* for photon energies from threshold to 2.4 GeV. The radiative branching ratio for the Sigma0(1385) relative to the Sigma0(1385) → Sigmapi0 channel was measured to be 0.021 +/- 0.008+0.004-0.007 corresponding to a partial width of 640 +/- 270+130-220 keV.

This thesis reports the results of a kinematically complete experiment designed to study the reaction $\pi\sp{+}$ d $\to\pi\sp{+}$ p n in a range of phase space accessible to the high energy pion channel at LAMPF. (The Los Alamos Meson Physics Facility, a part of the Los Alamos National Laboratory in New Mexico.) The kinematics were chosen to emphasize the reaction $\pi\sp{+}$ d $\to\Delta\sp{++}$ n, where the subsequent decay of the delta particle produces the observed final state. At $\Delta\sp{++}$ production angles of 55$\sp\circ$ and 91$\sp\circ$ in the reaction center of mass frame of reference, differential cross sections were measured at seven beam momenta between 312 MeV/c (corresponding to $\sqrt{\rm s}$ = 2.19 GeV) and 600 MeV/c ($\sqrt{\rm s}$ = 2.42 GeV). At beam momenta of 350 MeV/c and 425 MeV/c, data were taken at seven center of mass $\Delta\sp{++}$ production angles between 30$\sp\circ$ and 120$\sp\circ$. These excitation functions and angular distributions will provide tests for various theoretical approaches to understanding the nucleon-delta interaction. In particular, these data are well fit by a conventional relativistic Faddeev theory using no free parameters. Over most of the phase space, both the shape of the momentum spectra and the magnitude of the cross sections are reproduced by the model. In regions near the peak of the $\Delta\sp{++}$ mass distribution, but far from the quasi-free scattering peak, this model underestimates the data by a factor which increases with energy. This factor does not appear to depend on the $\Delta\sp{++}$ production angle. Some possible explanations of the discrepancy are explored.

The results of a partial wave analysis of the $K\sp+\bar K\sp0\pi\sp-$ system produced in the reaction$$\pi\sp-p \to K\sp+\bar K\sp0\pi\sp-n$$at 18 GeV/c are presented. A total of 5612 events in the mass range 1.2-1.8 GeV/c$\sp2$ was collected using Brookhaven National Laboratory's Multiparticle Spectrometer facility. The $K\sp+\bar K\sp-\pi\sp-$ mass spectrum shows two clear peaks: one at 1.285 $\pm$ 0.001 GeV/c$\sp2$ with width 0.022 $\pm$ 0.003 GeV/c$\sp2$ and one at 1.423 $\pm$ 0.004 GeV/c$\sp2$ with width 0.062 $\pm$ 0.005 GeV/c$\sp2.$ The results of the partial wave analysis show the lower mass peak to be approximately equal parts $J\sp{PG} = 1\sp{++}$ and 0$\sp{-+},$ both decaying to $a\sb0(980)\pi\sp-$ with essentially no background. The analysis of the higher mass peak shows two $J\sp{PG} = 0\sp{-+}$ states: one at 1.412 $\pm$ 0.002 GeV/c$\sp2$ with a width of 0.036 $\pm$ 0.012 decaying into $a\sb0(980)\pi\sp-,$ and one at 1.475 $\pm$ 0.006 GeV/c$\sp2$ with a width of 0.081 $\pm$ 0.014 GeV/c$\sp2$ decaying into $K\sp*(892)K.$ The $J\sp{PG} = 1\sp{++}$ wave in this region rises rapidly to a constant value and does not show resonant behavior. The phase-space background begins increasing rapidly at $K\sp*(892)K$ threshold. The dominant contribution to the total signal is from positive reflectivity waves only. This corresponds to natural spin-parity Reggion exchange, presumably $a\sb0$(980) or $a\sb2$(1320).

Measured inclusive $\Lambda,\ \bar\Lambda$ and K$\sbsp{S}{\circ}$ production cross sections and rapidity distributions for p interactions on nuclear targets of C, Cu and Pb are presented. Also described is a newly developed analysis program for the MPS detector that utilizes a new pattern recognition algorithm. Additionally, a new hyperon production procedure for the INC model is introduced.

This work involves thermal photon production from the Quark Gluon Plasma (QGP) and Hadronic Gas (HG) in heavy ion collisions. Using a 3D + 1 hydrodynamic model (MUSIC) to describe the evolution of the system after thermalization of a Au+Au collision, we compute the total production of thermal photons. We use effective models for mesonic interactions in HG and the quark gluon plasma. We compare photon production and elliptic flow from both sources and look at how the centrality and the equations of state influence the photon observables.We do this using ideal (non-dissipative) hydrodynamics, but also with viscous hydrodynamics. We examine the effects on the hydrodynamic properties (temperature, flow) and on the photon production of the inclusion of shear viscosity in the hydrodynamic equations. We then also look at another effect of viscosity, which is that the distribution functions of quarks and mesons need to be corrected. In our approach, we compute the necessary integrals for the viscous corrections and tabulate the results as a function of the temperature and energy. We then interpolate between these values. We look at how this affects photonic yield and elliptic flow. We also examine the effect of fluctuating initial conditions on the photon production.We find that viscosity does have a significant impact on the photonic yield, and an even more important effect on the elliptic flow of photons. Fluctuating initial conditions also lead to an appreciable effect on the yield. For all this, we restrict our study to photons with an energy between 0.2 and 4 GeV, which is the range where thermal photons account for a significant amount of the total yield. We show that photons make excellent probes for heavy ion collisions as they are very sensitive to many important theoretical concepts in our model of heavy ion collisions. / Cet ouvrage concerne la production de photons thermaux provenant du Plasma Quarks Gluons (PQG) et du gaz hadronique (GH) dans les collisions d'ions lourds. Nous utilisons un modèle hydrodynamique 3D + 1 (MUSIC) pour décrire le système après la thermalisation d'une collision Au+Au, avec lequel nous calculons la production totale de photons thermaux. Nous utilisons des modèles effectifs pour les interactions mésoniques dans le GH et dans le PQG. Nous comparons la production totale et l'écoulement elliptique des photons pour les deux sources et regardons comment la centralité et les équations d'état influencent les observables photoniques.Nous utilisons un modèle hydrodynamique idéal (non dissipatif), mais aussi un modèle incluant la viscosité. Nous regardons comment les propriétés hydrodynamiques (température, écoulement) sont modifiées par la viscosité de cisaillement et son effet sur la production de photons. De plus, la viscosité a aussi pour effet d'apporter une correction aux fonctions de distribution des quarks et des mesons. Dans notre approche, nous calculons numériquement les intégrales nécessaires pour les corrections visqueuses et tabulons les résultats en fonction de la température et de l'énergie du photon et interpolons entre ces valeurs. Nous examinons comment cela affecte la production totale de photons ainsi que l'écoulement elliptique. Nous regardons aussi l'effet des conditions initiales aléatoires.Nos calculs montrent que la viscosité a un effet significatif sur la production de photons, et surtout sur l'écoulement elliptique de ceux-ci. Les conditions initiales aléatoires ont aussi un effet très appréciable sur la production totale de photons. Pour tous les éléments mentionnés ci-haut, nos calculs sont restreints à des énergies du photon de 0.2 GeV à 4 GeV, qui correspond à la plage d'énergie pour laquelle les photons thermaux contribuent de façon significative à la production complète de photons (incluant tous les autres procédés pertinents). Nous montrons que les photons font d'excellentes sondes pour les collisions d'ions lourds car ils sont très sensibles aux concepts théoriques importants dont notre modèle dépend.

Several investigations involving strongly interacting matter at high temperature and density are pursued. First concentrating on relativistic heavy ion collisions slightly below the GeV/nucleon range, we perform studies of the equation of state (EOS) for nuclear matter. The non-equilibrium aspects of such collisions are simulated by the Boltzmann-Uehling-Uhlenbeck transport model with a momentum-dependent nuclear mean field. The EOS effects on the collective flow observables and dielectron spectra have been systematically and quantitatively examined by comparing with the experimental data gathered by the DIOGENE, Streamer Chamber, Plastic Ball, EOS TPC, E848H and DLS collaborations. The importance of the precise functional dependence of the nuclear mean field on the particle momentum, and the compressibility coefficient K of the nuclear matter are addressed. Using a simple coalescence model, we show that a quantitative connection between the composite flow and K can be established. In such nucleus-nucleus collisions, we also consider and discuss lepton pair production mechanisms. These include nucleon-nucleon bremsstrahlung, $ Delta$ decay, $ eta$ decay, and pion-pion annihilation. We then turn to lepton pair production in ultrarelativistic heavy ion collisions. We concentrate on pion-pion virtual bremsstrahlung in the soft limit M $<$ 300 MeV, and we make a quantitative comparison of various soft-photon-approximation (SPA) formulae with a full one-boson-exchange (OBE) calculation.