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A dark matter solution from the supersymmetric axion model

Description: We study the effect of the late decaying saxino (the scalar superpartner of the axion) and find out that there is a possible dark matter solution from a class of supersymmetric extensions of the invisible axion model. In this class of models, the saxino which decays into two axions acts as the late decaying particle which reconciles the cold dark matter model with high values of the Hubble constant. Recent observations of the Hubble constant are converging to H{sub 0} = 70--80 km sec{sup {minus}1} Mpc{sup {minus}1}, which would be inconsistent with the standard mixed dark matter model. This class of models provides a plausible framework for the alternative cold dark matter plus late decaying particle model, with the interesting possibility that both cold dark matter and the extra radiation consist of axion. 15 refs.
Date: May 1, 1996
Creator: Chang, Sanghyeon & Kim, Hang Bae
Partner: UNT Libraries Government Documents Department

Symplectic structure of isospin particles in Yang-Mills fields

Description: Using Dirac's constraint analysis, we explore the Hamiltonian formalism of isospin particles in external Yang-Mills fields without kinetic and potential energy term. We consider an example of isospin particle in 't Hooft-Polyakov magnetic monopole field and discuss possible quantization condition of magnetic charge in terms of geometric quantization.
Date: January 1, 1992
Creator: Oh, P.
Partner: UNT Libraries Government Documents Department

RG analysis of magnetic catalysis in dynamical symmetry breaking

Description: We perform the renormalization group analysis on the dynamical symmetry breaking under strong external magnetic field, studied recently by Gusynin, Miransky and Shovkovy. We find that any attractive four-Fermi interaction becomes strong in the low energy, thus leading to dynamical symmetry breaking. When the four-Fermi interaction is absent, the {beta}-function for the electromagnetic coupling vanishes in the leading order in 1/N. By solving the Schwinger-Dyson equation for the fermion propagator, we show that in 1/N expansion, for any electromagnetic coupling, dynamical symmetry breaking occurs due to the presence of Landau energy gap by the external magnetic field. 5 refs.
Date: May 1, 1996
Creator: Hong, Deog Ki & Kim, Youngman
Partner: UNT Libraries Government Documents Department

New dark matter candidates motivated from superstring derived unification

Description: Perturbative gauge coupling unification in realistic superstring models suggest the existence of additional heavy down-type quarks, beyond the minimal supersymmetric standard model. The mass scale of the heavy down-type quarks is constrained by requiring agreement between the measured low energy gauge parameters and the string-scale gauge coupling unification. These additional quarks arise and may be stable due to the gauge symmetry breaking by ``Wilson lines`` in the superstring models. We argue that there is a window in the parameter space within which this down-type quark is a good candidate for the dark matter. 18 refs.
Date: March 1, 1996
Creator: Chang, Sanghyeon; Coriano, C. & Faraggi, A.E.
Partner: UNT Libraries Government Documents Department

X-ray reflectivity study of gold films during sputter-deposition

Description: We performed in-situ x-ray reflectivity measurements of gold films during sputter-deposition on polished silicon substrates. The measurements were performed at several substrate temperatures and under two argon pressures. The gold surfaces were also examined by scanning tunneling microscopy after deposition to obtain their real-space topographic images. These images were used to complement the x-ray reflectivity measurements in determining the effect of argon pressure on the gold surface and its height-height difference functions. An approximation for height-height difference functions was employed to analyze the x-ray reflectivity data. The measured interface width during growth follows a simple power-law behavior consistent with recently developed dynamic scaling behavior. The scaling components, however, do not agree well with predictions based on some models in 2 + 1 dimensions.
Date: May 1, 1994
Creator: Chiarello, R.P.; You, H.Y. & Roberts, T.
Partner: UNT Libraries Government Documents Department

Sealing behaviour and hall conductivity of mixed-state hall effect in heavy-ion irradiated YBa{sub 2}Cu{sub 3}O{sub 7} crystals

Description: The Hall effect ({rho}{sub xy}) and longitudinal resistivity ({rho}{sub xx}) measured in YBa{sub 2}Cu{sub 3}O{sub 7} crystals before and after the irradiation of Sn and Xe ions. We found a clear evidence that the strong pinning induced by the columnar defects not only modifies the scaling behavior between the Hall resistivity {rho}{sub xy} and longitudinal resistivity {rho}{sub xx} but also affects the temperature dependence of the Hall conductivity. For the irradiated crystals with columnar defects, the scaling exponent {beta} of {rho}{sub xy} = A{rho}{sub xx}{sup {beta}} was found to be {beta} = 1.55 {+-} 0.1, whereas {beta} of the unirradiated one was larger than 1.8. In case of the Hall conductivity, the pinning strength dependence was also observed. The Hall conductivity after irradiation exhibited a clear deviation from that of the unirradiated crystal at low temperatures. These results are in a good agreement with the work by Wang et al. in which pinning plays an important role.
Date: December 31, 1995
Creator: Kim, D.H.; Shim, S.Y. & Kang, W.N.
Partner: UNT Libraries Government Documents Department

Lattice calculation of quarkonium decay matrix elements

Description: The authors calculate the NRQCD (nonrelativistic QCD) matrix elements for the decays of the lowest-lying S- and P-wave states of charmonium and bottomonium in quenched lattice QCD. They also compute the one-loop relations between the lattice and continuum matrix elements.
Date: September 1996
Creator: Bodwin, G. T.; Sinclair, D. K. & Kim, S.
Partner: UNT Libraries Government Documents Department

Effect of heavy-ion irradiation on transport properties of YBa{sub 2}Cu{sub 3}O{sub x} films

Description: Parallel columnar defects to the c axis and crossed columnar defects were introduced into these films by heavy-ion irradiation with dose equivalent to 1 or 2 T vortex density. The electrical transport properties including resistivity, critical current density, Hall resistivity were measured vs temperature, applied magnetic field, and fluence. The irreversibility line defined as onset of dissipation progressively shifted to higher temperature with dosage and showed its dependence on inclination angle. Critical current also showed a clear enhancement compared to unirradiated samples. The Hall scaling behavior and the Hall conductivity were modified after heavy-ion irradiation.
Date: December 31, 1996
Creator: Kim, D.H.; Shim, S.Y. & Park, J.H.
Partner: UNT Libraries Government Documents Department

Light-front view of the axial anomaly

Description: Motivated by an apparent puzzle of the light-front vacua incompatible with the axial anomaly, we have considered the two-dimensional massless Schwinger model for an arbitrary interpolating angle of the quantization surface. By examining spectral deformation of the Dirac sea under an external electric field semiclassically, we have found that the axial anomaly is quantization angle independent. This indicates an intricate nontrivial vacuum structure present even in the light-front limit.
Date: July 1, 1995
Creator: Ji, Chueng-Ryong & Rey, Soo-Jong
Partner: UNT Libraries Government Documents Department

Finite-temperature corrections in the dilated chiral quark model

Description: We calculate the finite-temperature corrections in the dilated chiral quark model using the effective potential formalism. Assuming that the dilaton limit is applicable at some short length scale, we interpret the results to represent the behavior of hadrons in dense and hot matter. We obtain the scaling law, f{sub {pi}}(T)/f{sub {pi}} = m{sub Q}(T)/m{sub Q} {approx_equal} m{sub {sigma}}(T)/m{sub {sigma}}while we argue, using PCAC, that pion mass does not scale within the temperature range involved in our Lagrangian. It is found that the hadron masses and the pion decay constant drop faster with temperature in the dilated chiral quark model than in the conventional linear sigma model that does not take into account the QCD scale anomaly. We attribute the difference in scaling in heat bath to the effect of baryonic medium on thermal properties of the hadrons. Our finding would imply that the AGS experiments (dense and hot matter) and the RHIC experiments (hot and dilute matter) will ``see`` different hadron properties in the hadronization exit phase.
Date: March 1, 1995
Creator: Kim, Y.; Lee, Hyun Kyu & Rho, M.
Partner: UNT Libraries Government Documents Department

Centrality and collision system dependence of antiproton production from p+A to Au+Au collisions at AGS energies

Description: Antiproton production in heavy ion collisions reflects subtle interplay between initial production and absorption by nucleons. Because the AGS energies (10--20 A{center_dot}GeV/c) are close to the antiproton production threshold, antiproton may be sensitive to cooperative processes such as QGP and hadronic multi-step processes. On the other hand, antiproton has been proposed as a probe of baryon density due to large N{anti N} annihilation cross sections. Cascade models predict the maximum baryon density reaches about 10 times the normal nucleus density in central Au+Au collisions, where the strong antiproton absorption is expected. In this paper, the authors show systematic studies of antiproton production from p+A to Au+Au collisions.
Date: December 1997
Creator: Sako, H.; Ahle, L.; Akiba, Y. & Collaboration, E802
Partner: UNT Libraries Government Documents Department

Particle production in Au + Au collisions from BNL E866

Description: In this article, we present recent results on particle production from Au+Au collisions at 11 A GeV/c obtained by the E866 experiment. The experiment studies the particle production in high baryon density matter created in central Au + Au collisions. Preliminary results of proton and pion production have been reported in previous Quark Matter conferences. Two particle correlation data for Au + Au collisions in this experiment are presented in another paper in this conference.
Date: November 1, 1996
Creator: Akiba, Y.; Hamagaki, H.; Homma, S. & Sako, H.
Partner: UNT Libraries Government Documents Department

{anti p} and {anti {Lambda}} production in Si+Au collisions at the AGS

Description: {anti {ital p}} and {anti {Lambda}} production in central Si + Au collisions has been measured by E589 at the BNL-AGS. Preliminary {ital m}{sub {perpendicular}} spectra are presented for {anti {ital p}}`s and {anti {Lambda}}`s. The {ital dn/dy} distribution for {anti {ital p}}`s is also presented. Based on the {anti {ital p}} and {anti {Lambda}} measurements, {anti {Lambda}}/{anti {ital p}} ratios are calculated in the rapidity range of 1.1-1.5.
Date: December 31, 1996
Creator: Wu, Yuedong & Collaboration, E802 /E859
Partner: UNT Libraries Government Documents Department

Composite particle production in relativistic Au+Au collisions at AGS: First results from the E866 forward spectrometer @ 2, 4, and 10.8 A{center_dot}GeV

Description: Particle spectra were measured for Au + Au collisions at 2, 4, and 10. 8 A{center_dot}GeV using the E866 spectrometers. Recent results on proton emission and composite particle production form the E866 forward spectrometer data taken in 1994 together with the first results from the 1995/6 AGS running period are presented. Preliminary results indicate a decrease in the coalescence scaling coefficient with increasing projectile energy and centrality.
Date: December 31, 1996
Creator: Ashktorab, K.
Partner: UNT Libraries Government Documents Department

Two particle correlations at mid-rapidity in Si+A and Au+Au from E859/E866

Description: Two particle correlation measurements for {ital Si-A} and {ital Au- Au} collisions from Brookhaven E859 and E866 are discussed. These measurements allow us, with some interpretation, to deduce the size of the participant region in a heavy ion collision. We show that various source parameterizations yield consistent results and we explore the dependence of the apparent source size on the pion yield.
Date: February 1, 1997
Creator: Baker, M.D. & Collaboration, E802
Partner: UNT Libraries Government Documents Department

Transverse momentum dependent two-pion Bose-Einstein correlations in Au + Au collisions at 11.6 A {center_dot} GeV/c

Description: Bose-Einstein correlations of {pi}{sup +}{pi}{sup +} and {pi}{sup {minus}}{pi}{sup {minus}} pairs collected by the BNL-E866 Forward Spectrometer in 11.6 A{center_dot}GeV/c Au + Au collisions have been measured. The data were analyzed using three-dimensional correlation functions parameterized by the Yano-Koonin-Potgoretskii and Bertsch-Pratt formalism to study transverse momentum dependent source parameters. Rapid decreases of longitudinal source radii and slower decreases in the transverse parameters with increasing transverse momentum were observed, which suggests a strong longitudinal and some transverse expansion. A freeze-out time {tau}{sub 0} was derived as 4.5--5 fm/c, under the assumption of the freeze-out temperature T = 130 MeV, and the duration of emission was found to be {delta}{tau} {approx} 2--4 fm/c.
Date: December 1998
Creator: Lee, J. H. & Collaboration, E866
Partner: UNT Libraries Government Documents Department

The finite size effect on the metal-insulator transition of MOCVD grown VO sub 2 films

Description: We studied the finite size effect on the metal-insulator phase transition and the accompanying tetragonal to monoclinic structural phase transition of VO{sub 2} films grown by MOCVD. X-ray diffraction measurements and electrical conductivity measurements were done as a function of temperature for VO{sub 2} films with out-of-plane particle size ranging from 60--310 {Angstrom}. Each Vo{sub 2} film was grown on a thin TiO{sub 2} buffer layer, which in turn was grown by MOCVD on a polished sapphire (112) substrate. The transition was found to be first order. As the out-of-plane particle size becomes larger, the transition temperature shifts and the transition width narrows. For the 60{Angstrom} film the transition was observed at {approximately}61{degrees}C with a transition width if {approximately}10{degrees}C, while for the 310{Angstrom} film the transition temperature was {approximately}59{degrees}C and the transition width {approximately} 2{degree}C. We also observed thermal hysteresis for each film, which became smaller with increasing particle size.
Date: November 1, 1991
Creator: Kim, Hyung Kook; Chiarello, R.P.; You, Hoydoo; Chang, M.H.L.; Zhang, T.J. & Lam, D.J.
Partner: UNT Libraries Government Documents Department

The finite size effect on the metal-insulator transition of MOCVD grown VO{sub 2} films

Description: We studied the finite size effect on the metal-insulator phase transition and the accompanying tetragonal to monoclinic structural phase transition of VO{sub 2} films grown by MOCVD. X-ray diffraction measurements and electrical conductivity measurements were done as a function of temperature for VO{sub 2} films with out-of-plane particle size ranging from 60--310 {Angstrom}. Each Vo{sub 2} film was grown on a thin TiO{sub 2} buffer layer, which in turn was grown by MOCVD on a polished sapphire (112) substrate. The transition was found to be first order. As the out-of-plane particle size becomes larger, the transition temperature shifts and the transition width narrows. For the 60{Angstrom} film the transition was observed at {approximately}61{degrees}C with a transition width if {approximately}10{degrees}C, while for the 310{Angstrom} film the transition temperature was {approximately}59{degrees}C and the transition width {approximately} 2{degree}C. We also observed thermal hysteresis for each film, which became smaller with increasing particle size.
Date: November 1, 1991
Creator: Kim, Hyung Kook; Chiarello, R. P.; You, Hoydoo; Chang, M. H. L.; Zhang, T. J. & Lam, D. J.
Partner: UNT Libraries Government Documents Department

Input shaping filter methods for the control of structurally flexible, long-reach manipulators

Description: Within the Environmental Restoration and Waste Management Program of the US Department of Energy, the remediation of single-shell radioactive waste storage tanks is one of the areas that challenge state-of-the-art equipment and methods. Concepts that utilize long-reach manipulators are being seriously considered for this task. Due to high payload capacity and high length-to-cross-section ratio requirements, these long-reach manipulator systems are expected to exhibit significant structural flexibility. To avoid structural vibrations during operation, various types of shaping filter methods have been investigated. A robust notch filtering method and an impulse shaping method were used as simulation benchmarks. In addition to that, two very different approaches have been developed and compared. One new approach, referred to as a ``feedforward simulation filter,`` uses imbedded simulation with complete knowledge of the system dynamics. The other approach, ``fuzzy shaping method,`` employs a fuzzy logic method to modify the joint trajectory from the desired end-position trajectory without precise knowledge of the system dynamics.
Date: November 1, 1993
Creator: Kwon, Dong-Soo; Hwang, Dong-Hwan; Babcock, S. M. & Burks, B. L.
Partner: UNT Libraries Government Documents Department

Electron yield XAFS study of evaporated Co/Pd multilayers with various thickness ratios of Co to Pd sublayers: Simulations of the Co K-edge XAFS and fourier transforms

Description: Electron-yield XAFS measurements using the NSLS were made on e-beam evaporated Co/Pd multilayers with various sublayer thicknesses and different thickness ratios of Co to Pd sublayers. The Co K-edge and the Pd K-edge XAFS data were obtained for the Co/Pd multilayers with sublayer thicknesses of 3{Angstrom}/ 4{Angstrom}, 15{Angstrom}/4{Angstrom}, 3{Angstrom}/15{Angstrom}, 2.1{Angstrom}/13.5{Angstrom}, and 2.2{Angstrom}/4.5{Angstrom}. Fourier transforms of Co K XAFS for most samples show a splitting of major peak, and the magnitude ratio of these split peaks varies systematically with the thickness ratio of the Pd sublayer to the Co sublayer, whereas the Fourier transforms of the Pd K XAFS for the same samples do not show a splitting of peaks. As a preliminary analysis, the Co K XAFS and the split peaks in the Fourier transform for the Co/Pd(3{Angstrom}/4{Angstrom}) case were simulated by using the FEFF calculations, and the Co K XAFS and the major peak in the fourier transform for the Co/Pd(15{Angstrom}/4{Angstrom}) case were also simulated consistently.
Date: November 1, 1992
Creator: Choi, M.; Joo, J. H.; Kim, S. K.; Kang, J. S.; Lee, Y. P.; Shin, S. C. et al.
Partner: UNT Libraries Government Documents Department

A preliminary improved test of the flavor independence of strong interactions

Description: The authors present an improved comparison of the strong couplings of gluons to light (u, d, and s), c, and b quarks, determined from multijet rates in flavor-tagged samples of hadronic Z{sup 0} decays recorded with the SLC Large Detector at the SLAC Linear Collider between 1993 and 1995. Flavor separation on the basis of lifetime and decay multiplicity differences among hadrons containing light, c, and b quarks was made using the SLD precision tracking system, yielding tags with high purity and low bias against {ge} 3-jet final states. They find: {alpha}{sub s}{sup uds}/{alpha}{sub s}{sup all} = 0.997 {+-} 0.011(stat) {+-} 0.011(syst) {+-} 0.005(theory), {alpha}{sub s}{sup c}/{alpha}{sub s}{sup all} = 0.984 {+-} 0.042 {+-} 0.053 {+-} 0.022, {alpha}{sub s}{sup b}/{alpha}{sub s}{sup all} = 1.022 {+-} 0.019 {+-} 0.023 {+-} 0.012.
Date: June 1, 1997
Creator: Abe, K.; Abe, K.; Akagi, T. & Collaboration, SLD
Partner: UNT Libraries Government Documents Department

Preliminary measurement of prompt D{sup {+-}} and D*{sup {+-}} meson production and D*{sup {+-}} spin alignment in hadronic Z{sup 0} decays

Description: The authors have measured the production rates as a function of scaled energy x of prompt charmed pseudoscalar D{sup {+-}} and vector D*{sup {+-}} mesons in hadronic Z{sup 0} decays. The prompt signal components were isolated from the background of D mesons from B hadron decays using impact parameters of reconstructed D{sup {+-}} {yields} K{sup {minus_plus}}{pi}{sup {+-}}{pi}{sup {+-}} and D*-daughter D{sup 0} {yields} K{sup {minus}}{pi}{sup +} and D{sup 0} {yields} K{sup {minus}}{pi}{sup +}{pi}{sup {minus}}{pi}{sup +} candidates. Using the combined meson production rates the authors have measured the fraction of hadronic Z{sup 0} decays into c{bar c}, R{sub c} = 0.182 {+-} 0.027 (stat.) {+-} 0.012 (syst.) (Preliminary). Comparison of the D*{sup {+-}} and D{sup {+-}} rates gives a direct probe of vector (V) vs. pseudoscalar (P) meson production for charmed quarks, and for x > 0.4 they have measured P{sub V} = V/(V + P) = 0.65 {+-} 0.09(stat.) {+-} 0.03(syst.) {+-} 0.03 (BR) (Preliminary). They have measured the degree of spin alignment of the D*{sup {+-}} mesons along their flight direction and find it to be consistent with zero. They compared the latter two results with QCD- and model-based predictions of charm-quark jet fragmentation.
Date: June 1, 1997
Creator: Abe, K.; Abe, K.; Akagi, T. & Collaboration, SLD
Partner: UNT Libraries Government Documents Department

Production of {pi}{sup {+-}}, K{sup {+-}}, K{sup 0}, K*{sup 0}, {phi}, p and {Lambda}{sup 0} in hadronic Z{sup 0} decays

Description: The authors have measured production rates as a function of momentum of the identified hadrons {pi}{sup +}, K{sup +}, K{sup 0}, K*{sup 0}, {phi}, p, {Lambda}{sup 0} and their antihadrons in inclusive hadronic Z{sup 0} decays, as well as separately in decays into light, c and b flavors. In addition they have compared hadron and antihadron production rates in light quark (rather than antiquark) jets. The SLD Cherenkov Ring Imaging Detector was used to identify charged hadrons. The vertex detector was used to tag high-purity samples of light- and b-flavor events. The electron beam polarization was used to tag samples of quark and antiquark jets. Clear flavor dependences are observed, consistent with expectations based upon measured production and decay properties of heavy hadrons. They use the light-flavor results to test the predictions of MLLA QCD and of various fragmentation models. Differences between hadron and antihadron production in light quark jets are observed at high momentum fraction, providing direct evidence that higher-momentum particles are more likely to contain a primary quark or antiquark, and they use these results to make a new direct measurement of strangeness suppression in the jet fragmentation process.
Date: June 1, 1997
Creator: Abe, K.; Abe, K.; Akagi, T. & Collaboration, SLD
Partner: UNT Libraries Government Documents Department

Jet Production at D0

Description: We report on preliminary measurements of the central ({vert_bar}{eta}{vert_bar}<0.5) inclusive jet cross section and the dijet angular distributions ({vert_bar}{eta}{vert_bar}<3) at {radical}s=1.8 TeV. The data were collected during the 1992-1993 and 1994-1995 runs at the Fermilab Tevatron p{anti p} Collider with the D0 detector. The measurements are in excellent agreement with next-to- leading order (NLO) QCD. Given the assumptions implicit in the theoretical models, we exclude quark compositeness to the 95% confidence level on a scale of {Lambda}{sub +}=2 TeV.
Date: August 1, 1997
Creator: Elvira, V. D.
Partner: UNT Libraries Government Documents Department