Showing papers by "Hyun-Chul Kim published in 1999"

Fully sealed, high-brightness carbon-nanotube field-emission display

Abstract: A fully sealed field-emission display 4.5 in. in size has been fabricated using single-wall carbon nanotube (CNT)-organic binders. The fabricated displays were fully scalable at low temperature, below 415 °C, and CNTs were vertically aligned using paste squeeze and surface rubbing techniques. The turn-on fields of 1 V/μm and field emission current of 1.5 mA at 3 V/μm (J=90 μA/cm2) were observed. Brightness of 1800 cd/m2 at 3.7 V/μm was observed on the entire area of a 4.5 in. panel from the green phosphor-indium–tin–oxide glass. The fluctuation of the current was found to be about 7% over a 4.5 in. cathode area.

Inclusive jet cross section in p p collisions at s = 1.8 tev

Abstract: We report on the preliminary measurement of the inclusive jet cross section for {vert_bar}{eta}{vert_bar} {le} 0.5 at {radical}s = 1.8 TeV. Two data sets with integrated luminosities of 91 pb{sup {minus}1} and 14 pb{sup {minus}1} were collected at the Fermilab Tevatron {ovr p}p Collider with the D0 detector. The inclusive jet cross sections are measured and reported as a function of transverse jet energy (35 GeV {le} E{sub T} {le} 470 GeV) are in excellent agreement with next-to-leading order QCD. 11 refs., 4 figs.

Limits on dark matter WIMPs using upward-going muons in the MACRO detector

Abstract: We perform an indirect search for weakly interacting massive particles (WIMPs) using the MACRO detector to look for neutrino-induced upward-going muons resulting from the annihilation of WIMPs trapped in the Sun and Earth. The search is conducted in various angular cones centered on the Sun and Earth to accommodate a range of WIMP masses. No significant excess over the background from atmospheric neutrinos is seen. We set experimental flux limits on the upward-going muon fluxes from the Sun and the Earth. These limits are used to constrain neutralino particle parameters from supersymmetric theory, including those suggested by recent results from DAMA-NaI. {copyright} {ital 1999} {ital The American Physical Society}

Inclusive jet cross section in p̄p collisions at √ = 1.8 TeV

Abstract: We have made a precise measurement of the central inclusive jet cross section at sqrt(s) = 1.8 TeV. The measurement is based on an integrated luminosity of 92 pb-1 collected at the Fermilab Tevatron pbar-p Collider with the D-Zero detector. The cross section, reported as a function of jet transverse energy (ET >= 60 GeV) in the pseudorapidity interval |eta| <= 0.5, is in good agreement with predictions from next-to-leading order quantum chromodynamics.

Simultaneous synthesis and densification of Ti5Si3 and Ti5Si3–20 vol% ZrO2 composites by field-activated and pressure-assisted combustion

Abstract: A method to simultaneously synthesize and consolidate the silicide Ti 5 Si 3 and the composite Ti 5 Si 3 –20 vol% ZrO 2 from powders of Ti, Si, and ZrO 2 was investigated Combustion synthesis was carried out under the combined effect of an electric field and mechanical pressure The final density of the products increased nearly linearly with the applied pressure Highly dense Ti 5 Si 3 and Ti 5 Si 3 –20 vol% ZrO 2 with relative densities of up to 98% were produced under the simultaneous application of a 60 MPa pressure and a 3000 A current on the reactant powders The percentages of the total shrinkage occurring before and during the synthesis reaction were 22 and 78% for the case of Ti 5 Si 3 , and 18 and 82% for the case of Ti 5 Si 3 –20 vol% ZrO 2 , respectively The respective Vickers microhardness values for these materials were 85 and 60 GPa From indentation crack measurements, the fracture toughness values for Ti 5 Si 3 and Ti 5 Si 3 –20 vol% ZrO 2 were calculated to be 3 and 9 MPa m 1/2 , respectively

Measurement of the top quark mass with the collider detector at fermilab

Abstract: We present a new measurement of the top quark mass in t{ovr t} events in which both W bosons from top quarks decay into leptons (e{nu},thinsp{mu}{nu}) . We use events collected by the CDF experiment from p{ovr p} collisions at {radical} (s) =1.8 TeV at the Tevatron collider. We measure a top quark mass of 167.4{plus_minus}10.3(stat){plus_minus}4.8( syst) GeV /c{sup 2} from a sample of eight events. We combine this result with previous CDF measurements in other decay channels to obtain a final mass value of 176.0{plus_minus}6.5 GeV /c{sup 2} . {copyright} {ital 1999} {ital The American Physical Society }

Searches for new physics in diphoton events in pp̄ collisions at √s = 1.8 TeV

Abstract: We present a detailed description of a search for anomalous production of missing E{sub T} (E/{sub T}), jets, leptons (e,{mu},{tau}), {ital b} quarks, or additional photons in events containing two isolated, central ({vert_bar}{eta}{vert_bar}{lt}1.0) photons with E{sub T}{gt}12 GeV. The results are consistent with standard model expectations, with the possible exception of one event that has, in addition to the two photons, a central electron, a high-E{sub T} electromagnetic cluster, and large E/{sub T}. We set limits using two specific SUSY scenarios for production of diphoton events with E/{sub T}. thinsp thinsp {copyright} {ital 1999} {ital The American Physical Society}

Search for the flavor-changing neutral current decays B+→μ+μ-K+ and B0→μ+μ-K*0

Abstract: We report on a search for the flavor-changing neutral current decays B{sup +} {yields} {mu}{sup +}{mu}{sup -}K{sup +} and B{sup 0} {yields} {mu}{sup +}{mu}{sup -}K{sup *0} using 88 pb{sup -1} of data from p{ovr p} collisions at sqrt[s] = 1.8 TeV, collected with the Collider Detector at Fermilab. Finding no evidence for these decays, we set upper limits on the branching fractions B(B{sup +} {yields} {mu}{sup +}{mu}{sup -}K{sup +})<5.2x10{sup -6} and B(B{sup 0} {yields} {mu}{sup +}{mu}{sup -}K{sup *0})<4.0x10{sup -6} at the 90% confidence level.

Measurement of bb¯ rapidity correlations in pp¯ collisions at s=1.8 TeV

Abstract: We report the first direct measurement of bb(bar sign) rapidity correlations in pp(bar sign) collisions at {radical}(s)=1.8 TeV. We select events with a high transverse momentum muon accompanied by a jet, and a second jet associated with a decay vertex displaced from the pp(bar sign) interaction vertex. Two independent samples are obtained corresponding to events with a forward (2.0<|{eta}|<2.6) or central (|{eta}|<0.6) muon. We measure the ratio of forward to central bb(bar sign) production to be 0.361{+-}0.033(stat){sub -0.031}{sup +0.015}(syst), in good agreement with the next-to-leading order QCD prediction 0.338{sub -0.097}{sup +0.014}. (c) 1999 The American Physical Society.

Search for B0s-B0s oscillations using the semileptonic decay B0s → φℓ + Xν

Abstract: A search for B{sub s}{sup 0}-{ovr B}{sub s}{sup 0} oscillations is performed in a sample of B{sub s}{sup 0} semileptonic decays collected using dilepton triggers at the Tevatron Collider during 1992-1995. The B{sub s}{sup 0} is reconstructed using phiv meson-lepton correlations; its initial flavor is determined with the second lepton in the event. From a signal of 1068 with a B{sub s}{sup 0} purity of 61%, we obtain a limit on the B{sub 2}{sup 0}-{ovr B}{sub s}{sup 0} oscillation frequency of {Delta}m{sub s}>5.8 ps{sup -1} at 95% confidence level.

Measurement of B0-B̄0 flavor oscillations using jet-charge and lepton flavor tagging in pp̄ collisions at √s=1.8 TeV

Abstract: We present a measurement of the mass difference {Delta}m{sub d} for the B{sup 0} meson and the statistical power of the b flavor tagging methods used. The measurement uses 90 pb{sup -1} of data from p{ovr p} collisions at sqrt[s]=1.8 TeV collected with the CDF detector. An inclusive lepton trigger is used to collect a large sample of B hadron semileptonic decays. The mass difference {Delta}m{sub d} is determined from the proper time dependence of the fraction of B hadrons that undergo flavor oscillations. The flavor at decay is inferred from the charge of the lepton from semileptonic B decay. The initial flavor is inferred by determining the flavor of the other B hadron produced in the collision, either from its semileptonic decay (soft-lepton tag) or from its jet charge. The measurement yields {Delta}m{sub d}=(0.500{+-}0.052{+-}0.043){Dirac_h} ps{sup -1}, where the first uncertainty is statistical and the second uncertainty is systematic. The statistical powers ({var_epsilon}D{sup 2}) of the soft-lepton and jet-charge flavor taggers are (0.91{+-}0.10{+-}0.11)% and (0.78{+-}0.12{+-}0.08)%, respectively.

Search for R-Parity violating supersymmetry using like-sign dielectrons in pp collisions at √ = 1.8 Tev

Abstract: We present a search for like-sign dielectron plus multijet events using $107{\mathrm{pb}}^{\ensuremath{-}1}$ of data in $p\overline{p}$ collisions at $\sqrt{s}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}1.8\mathrm{TeV}$ collected in 1992--1995 by the CDF experiment. Finding no events that pass our selection, we set $\ensuremath{\sigma}\ifmmode\times\else\texttimes\fi{}\mathrm{BR}$ limits on two supersymmetric processes that can produce this experimental signature: gluino-gluino or squark-antisquark production with $R$-parity violating decays of the charm squark or lightest neutralino via a nonzero ${\ensuremath{\lambda}}_{121}^{\ensuremath{'}}$ coupling. We compare our results to the next-to-leading order calculations for gluino and squark production cross sections and set lower limits on $M(\stackrel{\ifmmode \tilde{}\else \~{}\fi{}}{g})$, $M({\stackrel{\ifmmode \tilde{}\else \~{}\fi{}}{t}}_{1})$, and $M(\stackrel{\ifmmode \tilde{}\else \~{}\fi{}}{q})$.

Measurement of Z0 and Drell-Yan production cross sections using dimuons in p̄p collisions at √s=1.8TeV

Abstract: We present a measurement of Z 0 boson and Drell-Yan production cross sections in pp collisions at √s =1.8TeV using a sample of 107 pb -1 accumulated by the Collider Detector at Fermilab. The Drell-Yan cross section is measured in the mass range of M μμ > 40GeV/c 2 . We compare the measurements with the predictions of quantum chromodynamics in both leading order and next-to-leading order, incorporating the recent parton distribution functions. The measurements are consistent with the standard model expectations. ©1999 The American Physical Society.

Freeze-out parameters in central 158A (GeVPb)-Pb-208+Pbcollisions

Abstract: Neutral pion production in central 158A GeV [sup 208]Pb+ [sup 208] Pb collisions has been studied in the WA98 experiment at the CERN Super Proton Synchrotron. The [pi][sup 0] transverse mass spectrum has been analyzed in terms of a thermal model with hydrodynamic expansion. The high accuracy and large kinematic coverage of the measurement allow one to limit previously noted ambiguities in the extracted freeze-out parameters. The results are shown to be sensitive to the shape of the velocity distribution at freeze-out. [copyright] [ital 1999] [ital The American Physical Society ]

Evolution of through-thickness texture gradients in various steel sheets

Abstract: In order to investigate the evolution of through-thickness texture gradients in various ferritic steel sheets, samples of a deep drawing steel, a ferritic stainless steel and a low carbon steel were deformed by cold rolling with and without application of a lubricant during the deformation process. The hot band texture of all samples examined showed notable through-thickness texture gradients. The evolution of the cold rolling texture in the ferritic stainless steel and the low carbon steel in a solution-treated state was nearly independent of the lubrication during rolling. However, in the deep drawing steel and the as-received low carbon steel, the lubrication played an important role in the formation of the through-thickness texture gradients. Whereas the samples rolled with lubrication showed uniform textures throughout the sheet thickness, in the samples rolled without lubrication pronounced shear textures were observed on the sheet surface. The evolution of these through-thickness texture gradients is discussed in terms of inhomogeneous strain states computed by an FEM model.

Photoelectrochemical and corrosion properties of Fe{sub 2}O{sub 3}-TiO{sub 2} artificial passivation films

Abstract: Fe{sub 2}O{sub 3}-TiO{sub 2} artificial passivation films were formed on Pt substrates by low-pressure metallorganic chemical vapor deposition, and their corrosion resistance and photoelectrochemical properties were examined in acidic, neutral, and alkaline solutions. The corrosion resistance was examined by an anodic polarization test and the photocurrent response by a photoelectrochemical polarization test. The quantum yield maximum of the films depends on the cationic fraction of Ti{sup 4+} of the films, X{sub n}. It decreased in the range X{sub Ti} = 0.0--070, then increased in the range X{sub Ti} = 0.70--0.95, and finally decreased in the range X{sub Ti} = 0.95--1.0 with increasing X{sub Ti} value. The films in the ranges of X{sub Ti} = 0.0--0.70 and 0.95--1.0 had crystalline structure and the films in the range 0.70--0.95 had amorphous structure. Therefore, the increase in the quantum yield maximum in the range X{sub Ti} = 0.70--0.95 was attributed to the amorphous structure. Such a change in the quantum yield maximum was independent of solution pH. The corrosion resistance of the films increased with increasing X{sub Ti} value of the film in a 5.0 M HCl solution. Therefore, the films with X{sub Ti} = 0.70--0.95 can be concluded to have high quantummore » yield and high corrosion resistance.« less

Measurement of the B0B̄0 oscillation frequency using l-D*+ pairs and lepton flavor tags

Abstract: The oscillation frequency {delta}m{sub d} of B{sup 0}B(bar sign){sup 0} mixing is measured using the partially reconstructed semileptonic decay B(bar sign){sup 0}{yields}l{sup -}{nu}(bar sign)D{sup *+}X The data sample was collected with the CDF detector at the Fermilab Tevatron collider during 1992-1995 by triggering on the existence of two lepton candidates in an event, and corresponds to about 110 pb{sup -1} of p(bar sign)p collisions at {radical}(s)=18 TeV We estimate the proper decay time of the B(bar sign){sup 0} meson from the measured decay length and reconstructed momentum of the l{sup -}D{sup *+} system The charge of the lepton in the final state identifies the flavor of the B(bar sign){sup 0} meson at its decay The second lepton in the event is used to infer the flavor of the B(bar sign){sup 0} meson at production We measure the oscillation frequency to be {delta}m{sub d}=0516{+-}0099{sub -0035}{sup +} {sup 0029} ps{sup -1}, where the first uncertainty is statistical and the second is systematic (c) 1999 The American Physical Society

Search for New Particles Decaying to bb̄ in pp̄ Collisions at √s = 1.8 TeV

Abstract: We have used $87{\mathrm{pb}}^{\ensuremath{-}1}$ of data collected with the collider detector at Fermilab to search for new particles decaying to $b\overline{b}$. We present model-independent upper limits on the cross section for narrow resonances which exclude the color-octet technirho in the mass interval $350lMl440\mathrm{GeV}{/c}^{2}$. In addition, we exclude top-gluons, predicted in models of top-color-assisted technicolor, of width $\ensuremath{\Gamma}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}0.3M$ in the mass range $280lMl670\mathrm{GeV}{/c}^{2}$, of width $\ensuremath{\Gamma}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}0.5M$ in the mass range $340lMl640\mathrm{GeV}{/c}^{2}$, and of width $\ensuremath{\Gamma}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}0.7M$ in the mass range $375lMl560\mathrm{GeV}{/c}^{2}$.

Observation of the shadowing of cosmic rays by the Moon using a deep underground detector RID D-4317-2011

Abstract: Using data collected by the MACRO experiment during the years 1989--1996, we show evidence for the shadow of the Moon in the underground cosmic ray flux with a significance of 3.6\\ensuremath{\\sigma}. This detection of the shadowing effect is the first by an underground detector. A maximum-likelihood analysis is used to determine that the angular resolution of the apparatus is $0.9\\ifmmode^\\circ\\else\\textdegree\\fi{}\\ifmmode\\pm\\else\\textpm\\fi{}0.3\\ifmmode^\\circ\\else\\textdegree\\fi{}.$ These results demonstrate MACRO's capabilities as a muon telescope by confirming its absolute pointing ability and quantifying its angular resolution.

Measurement of the Bd0B̄d0 oscillation frequency using dimuon data in pp̄ collisions at √s = 1.8 TeV

Abstract: We present a measurement of the mass difference Δm d of the two B d 0 mass eigenstates. We use a flavor tagging method based on the lepton charge, in a sample of events with two muons at low transverse momentum. The sample corresponds to an integrated luminosity of 90 pb -1 collected by the Collider Detector at Fermilab. The result obtained is Δm d =0.503±0.064(stat)±0.071(syst) ps -1 . ©1999 The American Physical Society.

Search for a technicolor ωT particle in events with a photon and a b-quark jet at fermilab

Abstract: If the technicolor {omega}{sub T} particle exists, a likely decay mode is {omega}{sub T}{r_arrow}{gamma}{pi}{sub T} , followed by {pi}{sub T}{r_arrow}b{bar b} , yielding the signature {gamma}b{bar b} . We have searched 85 pb{sup {minus}1} of data collected by the CDF experiment at the Fermilab Tevatron for events with a photon and two jets, where one of the jets must contain a secondary vertex implying the presence of a b quark. We find no excess of events above standard model expectations. We express the result as an exclusion region in the M{sub {omega}{sub T}}-M{sub {pi}{sub T}} mass plane. {copyright} {ital 1999} {ital The American Physical Society }

Measurement of b quark fragmentation fractions in the production of strange and light B mesons in pp̄ collisions at √s=1.8 TeV

Abstract: A new technique to measure the ratio of b quark fragmentation fractions in $p\overline{p}$ collisions is described. Using a ${70\ensuremath{-}\mathrm{p}\mathrm{b}}^{\mathrm{\ensuremath{-}}1}$ sample of low-mass dimuon trigger data recorded with the Collider Detector at Fermilab, we identify B mesons by observing the double semileptonic decays $\stackrel{\ensuremath{\rightarrow}}{b}c\ensuremath{\mu}X$ with $\stackrel{\ensuremath{\rightarrow}}{c}s\ensuremath{\mu}X.$ By counting the numbers of ${K}^{*}{(892)}^{0},$ ${K}^{*}{(892)}^{+},$ and \ensuremath{\varphi}(1020) mesons produced in association with these muon pairs, we measure the ratio of strange to nonstrange B meson production to be ${f}_{s}{/(f}_{u}{+f}_{d})=[21.0\ifmmode\pm\else\textpm\fi{}3.6(\mathrm{stat}{)}_{\ensuremath{-}3.0}^{+3.8}(\mathrm{syst})]%.$ This measurement is the most precise available from hadron collisions to date. Limits on the branching fractions of semileptonic charm meson decays with ${K}_{1}(1270),$ ${K}_{1}^{*}(1410),$ and ${K}_{2}^{*}(1430)$ mesons in the final state are also obtained.

Effective Weak Chiral Lagrangian to ${\cal O} (p^4)$ in the Chiral Quark Model

Abstract: We investigate the $\Delta S = 1,2$ effective weak chiral Lagrangian within the framework of the chiral quark model. Starting from the effective four-quark operators, we derive the effective weak chiral action by integrating out the constituent quark fields. Employing the derivative expansion, we obtain the effective weak chiral Lagrangian to order ${\cal O} (p^4)$. We examine the contributions of the order ${\cal O} (N_c)$ to the ratio $g_{\underline{8}}/g_{\underline{27}}$, considering e.g. the quark axial-vector constant $g_{\rm A}$ different from unity. The low energy constants of the counterterms are also presented and discussed.