Showing papers by "Hyun-Chul Kim published in 1996"

Evidence for nu -bar micro--> nu -bare Oscillations from the LSND Experiment at the Los Alamos Meson Physics Facility.

Abstract: A search for ${\overline{\ensuremath{ u}}}_{\ensuremath{\mu}}\ensuremath{\rightarrow}{\overline{\ensuremath{ u}}}_{e}$ oscillations has been conducted at the Los Alamos Meson Physics Facility by using ${\overline{\ensuremath{ u}}}_{\ensuremath{\mu}}$ from ${\ensuremath{\mu}}^{+}$ decay at rest. The ${\overline{\ensuremath{ u}}}_{e}$ are detected via the reaction ${\overline{\ensuremath{ u}}}_{e}p\ensuremath{\rightarrow}{e}^{+}n$, correlated with a $\ensuremath{\gamma}$ from $\mathrm{np}\ensuremath{\rightarrow}d\ensuremath{\gamma}$ ( $2.2\mathrm{MeV}$). The use of tight cuts to identify ${e}^{+}$ events with correlated $\ensuremath{\gamma}$ rays yields 22 events with ${e}^{+}$ energy between 36 and $60\mathrm{MeV}$ and only $4.6\ifmmode\pm\else\textpm\fi{}0.6$ background events. A fit to the ${e}^{+}$ events between 20 and $60\mathrm{MeV}$ yields a total excess of ${51.0}_{\ensuremath{-}19.5}^{+20.2}\ifmmode\pm\else\textpm\fi{}8.0$ events. If attributed to ${\overline{\ensuremath{ u}}}_{\ensuremath{\mu}}\ensuremath{\rightarrow}{\overline{\ensuremath{ u}}}_{e}$ oscillations, this corresponds to an oscillation probability of ( $0.31\ifmmode\pm\else\textpm\fi{}0.12\ifmmode\pm\else\textpm\fi{}0.05$)%.

Evidence for neutrino oscillations from muon decay at rest.

Abstract: A search for \ensuremath{ u}${\mathrm{\ifmmode\bar\else\textasciimacron\fi{}}}_{\mathrm{\ensuremath{\mu}}}$\ensuremath{\rightarrow}\ensuremath{ u}${\mathrm{\ifmmode\bar\else\textasciimacron\fi{}}}_{\mathit{e}}$ oscillations has been conducted at the Los Alamos Meson Physics Facility using \ensuremath{ u}${\mathrm{\ifmmode\bar\else\textasciimacron\fi{}}}_{\mathrm{\ensuremath{\mu}}}$ from ${\mathrm{\ensuremath{\mu}}}^{+}$ decay at rest. The \ensuremath{ u}${\mathrm{\ifmmode\bar\else\textasciimacron\fi{}}}_{\mathit{e}}$ are detected via the reaction \ensuremath{ u}${\mathrm{\ifmmode\bar\else\textasciimacron\fi{}}}_{\mathit{ep}}$\ensuremath{\rightarrow}${\mathit{e}}^{+}$n, correlated with the 2.2 MeV \ensuremath{\gamma} from np\ensuremath{\rightarrow}d\ensuremath{\gamma}. The use of tight cuts to identify ${\mathit{e}}^{+}$ events with correlated \ensuremath{\gamma} rays yields 22 events with ${\mathit{e}}^{+}$ energy between 36 and 60 MeV and only 4.6\ifmmode\pm\else\textpm\fi{}0.6 background events. The probability that this excess is due entirely to a statistical fluctuation is 4.1\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}8}$. A ${\mathrm{\ensuremath{\chi}}}^{2}$ fit to the entire ${\mathit{e}}^{+}$ sample results in a total excess of 51.${0}_{\mathrm{\ensuremath{-}}19.5}^{+20.2}$\ifmmode\pm\else\textpm\fi{}8.0 events with ${\mathit{e}}^{+}$ energy between 20 and 60 MeV. If attributed to \ensuremath{ u}${\mathrm{\ifmmode\bar\else\textasciimacron\fi{}}}_{\mathrm{\ensuremath{\mu}}}$\ensuremath{\rightarrow}\ensuremath{ u}${\mathrm{\ifmmode\bar\else\textasciimacron\fi{}}}_{\mathit{e}}$ oscillations, this corresponds to an oscillation probability (averaged over the experimental energy and spatial acceptance) of (0.31\ifmmode\pm\else\textpm\fi{}0.12\ifmmode\pm\else\textpm\fi{}0.05)%. \textcopyright{} 1996 The American Physical Society.

Measurement of dijet angular distributions by the collider detector at fermilab

Abstract: We have used 106 pb^-1 of data collected in proton-antiproton collisions at sqrt(s)=1.8 TeV by the Collider Detector at Fermilab to measure jet angular distributions in events with two jets in the final state. The angular distributions agree with next to leading order (NLO) predictions of Quantum Chromodynamics (QCD) in all dijet invariant mass regions. The data exclude at 95% confidence level (CL) a model of quark substructure in which only up and down quarks are composite and the contact interaction scale is Lambda_ud(+) < 1.6 TeV or Lambda_ud(-) < 1.4 TeV. For a model in which all quarks are composite the excluded regions are Lambda(+) < 1.8 TeV and Lambda(-) < 1. 6 TeV.

Electromagnetic form factors of the SU(3) octet baryons in the semibosonized SU(3) Nambu-Jona-Lasinio model.

Abstract: The electromagnetic form factors of the SU(3) octet baryons are investigated in the semibosonized SU(3) Nambu{endash}Jona-Lasinio model (chiral quark-soliton model). The rotational 1/{ital N}{sub {ital c}} and strange quark mass corrections in linear order are taken into account. The electromagnetic charge radii of the nucleon and magnetic moments are also evaluated. It turns out that the model is in remarkably good agreement with the experimental data. {copyright} {ital 1996 The American Physical Society.}

Nucleon tensor charges in the SU(2) chiral quark-soliton model.

Abstract: We investigate the singlet ${g}_{T}^{(0)}$ and isovector ${g}_{T}^{(3)}$ tensor charges of the nucleon, which are deeply related to the first moment of the leading twist transversity quark distribution ${h}_{1}(x)$, in the SU(2) chiral quark-soliton model. With rotational $O(\frac{1}{{N}_{c}})$ corrections taken into account, we obtain ${g}_{T}^{(0)}=0.69$ and ${g}_{T}^{(3)}=1.45$ at a low normalization point of several hundreds MeV. Within the same approximation and parameters the model yields ${g}_{A}^{(0)}=0.36$, ${g}_{A}^{(3)}=1.21$ for axial charges and a correct octet-decuplet mass splitting. We show how the chiral quark-soliton model interpolates between the nonrelativistic quark model and the Skyrme model.

Measurement of correlated μ-b¯ jet cross sections in pp¯ collisions at s=1.8 TeV

Abstract: We report on measurements of differential $\mu - {\bar b}$ cross sections, where the muon is from a semi-leptonic $b$ decay and the ${\bar b}$ is identified using precision track reconstruction in jets. The semi-differential correlated cross sections, d$\sigma$/d$\Et^{{\bar b}}$, d$\sigma$/d$\pt^{{\bar b}}$, and d$\sigma$/d$\delta\phi(\mu - {\bar b})$ for $\pt^{\mu}>$~9 GeV/c, $|\eta^{\mu}| $~10 GeV, $|\eta^{{\bar b}}|<$~1.5, are presented and compared to next-to-leading order QCD calculations.

Measurement of σB(W→ev) and σB(Z0→e+e-) in pp̄ collisions at √s = 1.8 TeV

Abstract: We present a measurement of $\sigma \cdot B(W \to e u)$ and $\sigma \cdot B(Z^0 \to e^+e^-)$ in proton - antiproton collisions at $\sqrt{s} =1.8$ TeV using a significantly improved understanding of the integrated luminosity. The data represent an integrated luminosity of 19.7 pb$^{-1}$ from the 1992-1993 run with the Collider Detector at Fermilab (CDF). We find $\sigma \cdot B(W \to e u) = 2.49 \pm 0.12$~nb and $\sigma \cdot B(Z^0 \to e^+e^-) = 0.231 \pm 0.012$~nb.

Ratios of bottom meson branching fractions involving J/ psi mesons and determination of b quark fragmentation fractions.

Abstract: We report a measurement of the ratios of the decay rates of the ${B}^{+}$, ${B}^{0}$, and ${B}_{s}^{0}$ mesons into exclusive final states containing a $\frac{J}{\ensuremath{\psi}}$ meson. The final states were selected from 19.6 pb-1 of $p\overline{p}$ collisions recorded by the Collider Detector at Fermilab. These data are interpreted to determine the $b$ quark fragmentation fractions ${f}_{u}$, ${f}_{d}$, and ${f}_{s}$. We also determine the branching fractions for the decay modes ${B}^{+}\ensuremath{\rightarrow}\frac{J}{\ensuremath{\psi}{K}^{+}}$, ${B}^{+}\ensuremath{\rightarrow}\frac{J}{\ensuremath{\psi}{K}^{*}{(892)}^{+}}$, ${B}^{0}\ensuremath{\rightarrow}\frac{J}{\ensuremath{\psi}{K}^{0}}$, ${B}^{0}\ensuremath{\rightarrow}\frac{J}{\ensuremath{\psi}{K}^{*}{(892)}^{0}}$, and ${B}_{s}^{0}\ensuremath{\rightarrow}\frac{J}{\ensuremath{\psi}\ensuremath{\varphi}(1020)}$. We discuss the implications of these measurements to $B$ meson decay models.

Reconstruction of B0→J/ΨKS0 and Measurement of Ratios of Branching Ratios Involving B→J/ΨK* and B+→J/ΨK+

Abstract: We report on the reconstruction of the decay mode B{sup 0o} {yields} J/{psi}K{sup 0}{sub s} using 193 pb{sup -1} of data collected by the Collider Detector at Fermilab in p{bar p} collisions at sqrt[s] = 18 TeV A signal of 418{+-}69 events, with a signal-to-background ratio of 9:1, is observed Three additional decay modes B{sup +} {yields} J/{psi}K{sup +}, B{sup 0} {yields} J/{psi}K{sup *}(892){sup 0}, and B{sup +} {yields} J/{psi}K{sup *}(892){sup +} are reconstructed We measure three ratios of branching ratios, each one relative to the B{sup +} {yields} J/{psi}K{sup +} mode We also report the ratio of decay rates, {gamma}(B {yields} J/{psi}K{sup *})/{gamma}(B {yields} J/{psi}K), for the vector-vector relative to the vector-pseudoscalar modes, to be 132{+-}023(stat){+-}016(syst)

Search for charged Higgs boson decays of the top quark using hadronic τ decays

Abstract: We present the result of a search for charged Higgs boson decays of the top quark, produced in $p\overline{p}$ collisions at $\sqrt{s}=1.8$ TeV. When the charged Higgs boson is heavy and decays to a $\ensuremath{\tau}$ lepton, which subsequently decays hadronically, the resulting events have a unique signature: large missing transverse energy and the low-charged-multiplicity $\ensuremath{\tau}$. Data collected in 1992 and 1993 at the Collider Detector at Fermilab, corresponding to 18.7\ifmmode\pm\else\textpm\fi{}0.7 ${\mathrm{pb}}^{\ensuremath{-}1}$, exclude new regions of combined top quark and charged Higgs boson mass, in extensions to the standard model with two Higgs doublets.

Properties of Jets in W Boson Events from 1.8 TeV p¯p Collisions

Abstract: We present a study of events with Z bosons and hadronic jets produced in {bar p}p collisions at a center-of-mass energy of 1.8 TeV. The data consist of 6708 Z{yields}e{sup +}e{sup -} decays from 106 pb{sup -1} of integrated luminosity collected using the CDF detector at the Fermilab Tevatron Collider. The Z+{ge}n jet cross sections and jet production properties have been measured for n = 1 to 4. The data are compared to predictions of leading-order QCD matrix element calculations with added gluon radiation and simulated parton fragmentation.

Search for chargino-neutralino production in pp collisions at s=1.8 tev

Abstract: We have searched for chargino-neutralino production ({tilde {xi}}{sub 1}{sup {+-}}{tilde {xi}}{sub 2}{sup 0}) in 1.8 TeV p{bar p} collisions, followed by their leptonic decays {tilde {xi}}{sub 1}{sup {+-}}{yields}{tilde {xi}}{sub 1}{sup 0}{ell}{sup {+-}}{nu} and {tilde {xi}}{sub 2}{sup 0}{yields}{tilde {xi}}{sub 1}{sup 0}{ell}{sup +}{ell}{sup -}. These trilepton events are expected within a framework of the minimal supersymmetric standard model (MSSM). In a 19.1 pb{sup -1} data sample collected with a Collider Detector at Fermilab, no trilepton events were observed. Upper limits on {sigma}(p{bar p} {yields}{tilde {xi}}{sub 1}{sup {+-}}{tilde {xi}}{sub 2}{sup 0})BR({tilde {xi}}{sub 1}{sup {+-}}{tilde {xi}}{sub 2}{sup 0}{yields}3{ell}+X) were obtained for various MSSM parameter space regions, yielding new 95% confidence level lower limits for the neutralino ({tilde {xi}}{sub 2}{sup 0}) mass which extend as high as 49 GeV/c{sup 2}.

Search for flavor-changing neutral current B meson decays in pp̄ collisions √s = 1.8 Te V

Abstract: We report on a search for the flavor-changing neutral current decays B{sub d,s}{sup 0}{yields}{mu}{sup +}{mu}{sup -}, B{sup +}{yields}{mu}{sup +}{mu}{sup -}K{sup +}, and B{sup 0}{yields}{mu}{sup +}{mu}{sup -}K*{sup 0} using data from p{bar p} collisions at {radical}s= 1.8 TeV, collected with the Collider Detector at Fermilab during the 1992-1993 running period. We find no indication of such decays and we set the following 90% confidence level upper limits on branching ratios: B(B{sup 0}{yields}{mu}{sup +}{mu}{sup -})<1.6x10{sup -6}, B(B{sub s}{sup 0}{yields}{mu}{sup +}{mu}{sup -})<8.4 x 10{sup -6}, B(B{sup +}{yields}{mu}{sup +}{mu}{sup -}K{sup +})<1.0x10{sup -5}, and B(B{sup 0}{yields}{mu}{sup +}{mu}{sup -}K*{sup 0})<2.5x10{sup -5}.

Baryons as non-topological chiral solitons

Abstract: The present review gives a survey of recent developments and applications of the Nambu--Jona-Lasinio model with $N_f=2$ and $N_f=3$ quark flavors for the structure of baryons. The model is an effective chiral quark theory which incorporates the SU(N$_f$)$_L\otimes$SU(N$_f$)$_R\otimes$U(1)$_V$ approximate symmetry of Quantum chromodynamics. The approach describes the spontaneous chiral symmetry breaking and dynamical quark mass generation. Mesons appear as quark-antiquark excitations and baryons arise as non-topological solitons with three valence quarks and a polarized Dirac sea. For the evaluation of the baryon properties the present review concentrates on the non-linear Nambu--Jona-Lasinio model with quark and Goldstone degrees of freedom which is identical to the Chiral quark soliton model obtained from the instanton liquid model of the QCD vacuum. In this non-linear model, a wide variety of observables of baryons of the octet and decuplet is considered. These include, in particular, electromagnetic, axial, pseudoscalar and pion nucleon form factors and the related static properties like magnetic moments, radii and coupling constants of the nucleon as well as the mass splittings and electromagnetic form factors of hyperons. Predictions are given for the strange form factors, the scalar form factor and the tensor charge of the nucleon.

Measurement of the branching fraction B(B+u→J/ψπ+) and Search for B+c→J/ψπ+

Abstract: We report on a measurement of the branching fraction of the Cabibbo-suppressed decay ${B}_{u}^{+}\ensuremath{\rightarrow}J/\ensuremath{\psi}{\ensuremath{\pi}}^{+}$, where $J/\ensuremath{\psi}\ensuremath{\rightarrow}{\ensuremath{\mu}}^{+}{\ensuremath{\mu}}^{\ensuremath{-}}$. The data were collected by the Collider Detector at Fermilab during 1992--1995 and correspond to an integrated luminosity of $110{\mathrm{pb}}^{\ensuremath{-}1}$ in $\overline{p}p$ collisions at $\sqrt{s}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}1.8\phantom{\rule{0ex}{0ex}}\mathrm{TeV}$. A signal of ${28}_{\ensuremath{-}9}^{+10}$ events is observed and we determine the ratio of branching fractions $B({B}_{u}^{+}\ensuremath{\rightarrow}J/\ensuremath{\psi}{\ensuremath{\pi}}^{+})/B({B}_{u}^{+}\ensuremath{\rightarrow}J/\ensuremath{\psi}{K}^{+})$ to be $[{5.0}_{\ensuremath{-}1.7}^{+1.9}(\mathrm{stat})\ifmmode\pm\else\textpm\fi{}0.1(\mathrm{syst})]%$. Using the world average value for $B({B}_{u}^{+}\ensuremath{\rightarrow}J/\ensuremath{\psi}{K}^{+})$, we calculate the branching fraction $B({B}_{u}^{+}\ensuremath{\rightarrow}J/\ensuremath{\psi}{\ensuremath{\pi}}^{+})$ to be $({5.0}_{\ensuremath{-}1.9}^{+2.1})\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}5}$. We also search for the decay ${B}_{c}^{+}\ensuremath{\rightarrow}J/\ensuremath{\psi}{\ensuremath{\pi}}^{+}$ and report a $95%$ confidence level limit on $\ensuremath{\sigma}({B}_{c}^{+})B({B}_{c}^{+}\ensuremath{\rightarrow}J/\ensuremath{\psi}{\ensuremath{\pi}}^{+})/\ensuremath{\sigma}({B}_{u}^{+})B({B}_{u}^{+}\ensuremath{\rightarrow}J/\ensuremath{\psi}{K}^{+})$ as a function of the ${B}_{c}^{+}$ lifetime.

Improved measurement of the $\bar{B}^0$ and $B^{-}$ meson lifetimes

Abstract: The lifetimes of theB 0 andB + mesons have been measured with theAleph detector at LEP, using approximately 3 million hadronic Z decays collected in the period 1991–1994. In the first of three methods, semileptonic decays ofB 0 andB + mesons were partially reconstructed by identifying events containing a lepton with an associatedD*− orD¯0 meson. The second method used fully reconstructedB 0 andB + mesons. The third method, used to measure theB 0 lifetime, employed a partial reconstruction technique to identifyB 0→D*− π + X decays. The combined results are τ0=1.55±0.06±0.03ps,τ+=1.58±0.09±0.03ps,τ+τ0=1.03±0.08±0.02.

Search for chargino-neutralino production in pp̄ collisions at s=1.96TeV

Abstract: The authors present a search for the associated production of charginos and neutralinos in p{bar p} collisions at {radical}s = 1.96 TeV. The data were collected at the Collider Detector at Fermilab (CDF II) and correspond to integrated luminosities between 0.7 and 1.0 fb{sup -1}. They look for final states with one high-p{sub T} electron or muon, and two additional leptons. The results are consistent with the standard model expectations, and they set limits on the cross section as a function of the chargino mass in three different supersymmetric scenarios. For a specific MSSM scenario with no slepton mixing they set a 95% C.L. limit at 151 GeV/c{sup 2}.

Strange vector form factors of the nucleon in the SU(3) chiral quark-soliton model with the proper kaonic cloud

Abstract: The strange vector form factors are evaluated in the range between $Q^2=0$ and $Q^2=1\ \mbox{GeV}^2$ in the framework of the SU(3) chiral quark-soliton model (or semi-bosonized SU(3) Nambu-Jona-Lasinio model). The rotational $1/N_c$ and $m_s$ corrections are taken into account up to linear order. Taking care of a proper Yukawa-tail of the kaonic cloud, we get $\langle r^{2}\rangle^{\rm Sachs}_{s}=-0.095\; \mbox{fm}^2$ and $\mu_s = -0.68\;\mu_N$. The results are compared with several different models.

Adaptive Nonlinear Control of Interior Permanent Magnet Synchronous Motor with Maximum Torque Control

Abstract: An adaptive nonlinear control of an interior permanent magnet (IPM) synchronous motor with maximum torque control is proposed. In the conventional servo drive system, the controller is designed under the assumption that the electrical dynamics are neglected by the field oriented control and current control. This yields an acceptable performance for low performance drive applications due to the large time scale separation between the electrical and mechanical dynamics. However, for the high performance applications, the conventional controller often fails to perform satisfactorily. To overcome this problem, an input-output linearization technique will be applied to the speed tracking control of the IPM synchronous motor. Using this control scheme, the nonlinear model can be effectively linearized, and the speed error dynamics can be specified using the linear-based model. This control technique, however, gives an unsatisfactory output performance under the mismatch of the system parameters and load condition, which is caused by the incomplete linearization. For the robust output response, the controller parameters will be estimated by a model reference adaptive technique where the load torque and the magnitude of the flux linkage are estimated. These estimated parameters will be used for the input-output linearization to obtain the robust control performance under the parameter variations. Also, to operate the IPM synchronous motor for the maximum torque-per-current control, the estimated flux linkage is employed for the generation of the d-axis current command. The robustness and the output dynamic performance of the proposed control scheme are verified through the computer simulations.

Top quark soliton and its anomalous chromomagnetic moment

Abstract: We show that under the assumption of dynamical symmetry breaking of electroweak interactions by a top quark condensate, motivated by the top mode standard model, the top quark in this effective theory can be considered then as a chiral color soliton. This is realized in an effective four-fermion interaction with chiral $\mathrm{SU}{(3)}_{c}$ as well as $\mathrm{SU}{(2)}_{L}\ensuremath{\bigotimes}{\mathrm{U}}_{Y}(1)$ symmetry. In the pure top quark sector the soliton consists of a top valence quark and a Dirac sea of top quarks and top antiquarks coupled to a color octet of Goldstone pions. The mass spectra, isoscalar quadratic radii, and the anomalous chromomagnetic moment because of a nontrivial color form factor are calculated with zero and finite current top quark masses and effects at the hadron colliders are discussed. The anomalous chromomagnetic moment turns out to have a value consistent with the top quark production rates of the D0 and CDF measurements.

Light particle-evaporation residue coincidences for the 79Br+27Al system at 11.8 MeV/nucleon.

Abstract: Evaporation residues (ER) of {ital Z}=34{endash}43 are measured in singles and in coincidence with emitted protons, deuterons, tritons, and alpha particles. Measurements are done with a large detector array that covers the scattering angles from 2.5{degree} to 25{degree}. The energy centroids of the coincidence spectra of the protons are reasonably well described by statistical model calculations assuming complete fusion, although those for the deuterons and tritons are not. The {alpha}-particle spectra are significantly different than the calculated ones. The slopes of the high energy spectra of the protons required a level density parameter {ital a}{approx_gt}{ital A}/12. Comparisons between the experimental ER singles spectra and complete fusion calculations show small deviations that can be explained by incomplete fusion however, when analyzed in coincidence with light particles a very good description with complete fusion is found especially if the emission of intermediate mass fragments is included in the calculations. {copyright} {ital 1996 The American Physical Society.}