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  • 2000-2004  (24)
  • 1980-1984
  • 2002  (24)
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  • 2000-2004  (24)
  • 1980-1984
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  • 1
    Electronic Resource
    Electronic Resource
    Search for single leptoquark and squark production in electron-photon scattering at $\sqrt{s_{\rm ee}}=189$ GeV at LEP (2002)
    Springer
    The European physical journal 23 (2002), S. 1-11 
    Details
    ISSN: 1434-6052
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract. A search for first generation scalar and vector leptoquarks (LQ) as well as for squarks ( $\tilde{\mbox{q}}$ ) in R-parity violating SUSY models with the direct decay of the $\tilde{\mbox{q}}$ into Standard Model particles has been performed using e $^+$ e $^-$ collisions collected with the OPAL detector at LEP at an e $^+$ e $^-$ centre-of-mass energy $\sqrt{s_{\rm ee}}$ of 189 GeV. The data correspond to an integrated luminosity of about 160 pb $^{-1}$ . The dominant process for this search is $\mbox{eq}\to\LQ/\tilde{\mbox{q}}\to\mbox{eq},\nu\mbox{q}$ , where a photon, which has been radiated by one of the beam electrons, serves as a source of quarks. The numbers of selected events found in the two decay channels are in agreement with the expectations from Standard Model processes. This result allows to set lower limits at the 95% confidence level on the mass of first generation scalar and vector leptoquarks, and of squarks in R-parity violating SUSY models. For Yukawa couplings $\lambda$ to fermions larger than $\sqrt{4\pi\alpha_{\rm em}}$ , the mass limits range from 121 GeV $/c^2$ to $175$ GeV $/c^2$ ( $149$ GeV $/c^2$ to $188$ GeV $/c^2$ ) depending on the branching ratio $\beta$ of the scalar (vector) leptoquark state. Furthermore, limits are set on the Yukawa couplings $\lambda$ for leptoquarks and $\lambda'_{1jk}$ for squarks, and on $\beta$ as a function of the scalar leptoquark/squark mass.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s100520100859
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  • 2
    Electronic Resource
    Electronic Resource
    Search for Yukawa Production of a light neutral Higgs Boson at LEP (2002)
    Springer
    The European physical journal 23 (2002), S. 397-407 
    Details
    ISSN: 1434-6052
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract. Within a Two-Higgs-Doublet Model (2HDM) a search for a light Higgs boson in the mass range of 4–12 GeV has been performed in the Yukawa process $\mathrme^+ \mathrme^-\rightarrow \mathrm{b}\bar{\mathrm{b}}\mathrm{A}/\mathrm{h}\rightarrow\mathrm{b} \bar{\mathrm{b}}\tau^+\tau^-$ , using the data collected by the OPAL detector at LEP between 1992 and 1995 in $\mathrme^+ \mathrme^-$ collisions at about 91 GeV centre-of-mass energy. A likelihood selection is applied to separate background and signal. The number of observed events is in good agreement with the expected background. Within a CP-conserving 2HDM type II model the cross-section for Yukawa production depends on $\xi^{\mathrm{A}}_d=|\tan\beta|$ and $\xi^{\mathrm{h}}_d=|\sin\alpha/\cos\beta|$ for the production of the CP-odd A and the CP-even h, respectively, where $\tan\beta$ is the ratio of the vacuum expectation values of the Higgs doublets and $\alpha$ is the mixing angle between the neutral CP-even Higgs bosons. From our data 95% C.L. upper limits are derived for $\xi^{\mathrm{A}}_d$ within the range of 8.5 to 13.6 and for $\xi^{\mathrm{h}}_d$ between 8.2 to 13.7, depending on the mass of the Higgs boson, assuming a branching fraction into $\tau^+\tau^-$ of 100%. An interpretation of the limits within a 2HDM type II model with Standard Model particle content is given. These results impose constraints on several models that have been proposed to explain the recent BNL measurement of the muon anomalous magnetic moment.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s100520200896
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  • 3
    Electronic Resource
    Electronic Resource
    The supersymmetric Ward identities on the lattice (2002)
    Springer
    The European physical journal 23 (2002), S. 719-734 
    Details
    ISSN: 1434-6052
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract. Supersymmetric (SUSY) Ward identities are considered for the N=1 SU(2) SUSY Yang-Mills theory discretized on the lattice with Wilson fermions (gluinos). They are used in order to compute non-perturbatively a subtracted gluino mass and the mixing coefficient of the SUSY current. The computations were performed at gauge coupling $\beta=2.3$ and hopping parameter $\kappa\!=\!0.1925$ , 0.194, 0.1955 using the two-step multi-bosonic dynamical-fermion algorithm. Our results are consistent with a scenario where the Ward identities are satisfied up to O(a) effects. The vanishing of the gluino mass occurs at a value of the hopping parameter which is not fully consistent with the estimate based on the chiral phase transition. This suggests that, although SUSY restoration appears to occur close to the continuum limit of the lattice theory, the results are still affected by significant systematic effects.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s100520200898
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  • 4
    Electronic Resource
    Electronic Resource
    Final results of magnetic monopole searches with the MACRO experiment (2002)
    Springer
    The European physical journal 25 (2002), S. 511-522 
    Details
    ISSN: 1434-6052
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract. We present the final results obtained by the MACRO experiment in the search for GUT magnetic monopoles in the penetrating cosmic radiation, for the range $4\times 10^{-5}〈 \beta 〈 1$ . Several searches with all the MACRO sub-detectors (i.e. scintillation counters, limited streamer tubes and nuclear track detectors) were performed, both in stand alone and combined ways. No candidates were detected and a 90% Confidence Level (C.L.) upper limit to the local magnetic monopole flux was set at the level of $1.4\times 10^{-16}$ cm-2 s-1 sr-1. This result is the first experimental limit obtained in direct searches which is well below the Parker bound in the whole $\beta$ range in which GUT magnetic monopoles are expected.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1140/epjc/s2002-01046-9
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  • 5
    Electronic Resource
    Electronic Resource
    Inclusive semileptonic branching ratios of b hadrons produced in Z decays (2002)
    Springer
    The European physical journal 22 (2002), S. 613-626 
    Details
    ISSN: 1434-6052
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract. A measurement of the inclusive semileptonic branching ratios of b hadrons produced in Z decay is presented, using four million hadronic events collected by the ALEPH detector from 1991 to 1995. Electrons and muons are selected opposite to b-tagged hemispheres. Two different methods are explored to distinguish the contributions from direct ${{\mathrm b}\to{\mathrm{X}}\ell \nu}$ and cascade ${{\mathrm b}\to{\mathrm c}\to{\mathrm X} \ell \nu}$ decays to the total lepton yield. One is based on the lepton transverse momentum spectrum, the other makes use of the correlation between the charge of the lepton and charge estimators built from tracks in the opposite hemisphere of the event. The latter method reduces the dependence on the modelling of semileptonic b decays. The results obtained by averaging the two techniques are \begin{eqnarray} {\mathrm{BR}}({\mathrm b}\to{\mathrm{X}} \ell \nu)& = & 0.1070 \pm 0.0010 _{\mathrm{stat}} \pm 0.0023 _{\mathrm{syst}} \pm 0.0026 _{\mathrm{model}} , \nonumber {\mathrm{BR}}({\mathrm b}\to{\mathrm c}\to{\mathrm X} \ell \nu)& = & 0.0818 \pm 0.0015 _{\mathrm{stat}} \pm 0.0022 _{\mathrm{syst}} {^{+0.0010} _{-0.0014}} _{\mathrm{model}} . \nonumber \end{eqnarray}
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s100520100851
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  • 6
    Electronic Resource
    Electronic Resource
    Dijet production in neutral current deep inelastic scattering at HERA (2002)
    Springer
    The European physical journal 23 (2002), S. 13-27 
    Details
    ISSN: 1434-6052
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract. Dijet cross sections in neutral current deep inelastic ep scattering have been measured in the range $10 〈 Q^2 〈 10^4\mbox{GeV}^2$ with the ZEUS detector at HERA using an integrated luminosity of 38.4 pb $^{-1}$ . The cross sections, measured in the Breit frame using the $k_T$ jet algorithm, are compared with next-to-leading-order perturbative QCD calculations using proton parton distribution functions. The uncertainties of the QCD calculations have been studied. The predictions are in reasonable agreement with the measured cross sections over the entire kinematic range.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s100520100845
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    Paper (German National Licenses)
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  • 7
    Electronic Resource
    Electronic Resource
    Searches for neutral Higgs bosons in ${\mathrm e}^+{\mathrm e}^-$ collisions from $\sqrt{s} = 191.6$ to 201.7 GeV (2002)
    Springer
    The European physical journal 23 (2002), S. 409-435 
    Details
    ISSN: 1434-6052
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract. Neutral Higgs bosons of the Standard Model (SM) and the Minimal Supersymmetric Standard Model (MSSM) were searched for in the data collected in 1999 by the DELPHI experiment at centre-of-mass energies between 191.6 and 201.7 GeV with a total integrated luminosity of 228 pb $^{-1}$ . These analyses, in combination with our results at lower energies, set 95% confidence level lower mass bounds on the Standard Model Higgs boson (107.3 GeV/ $c^2$ ) and on the lightest neutral scalar (85.9 GeV/ $c^2$ ) and neutral pseudoscalar (86.5 GeV/ $c^2$ ) Higgs bosons in representative scans of the MSSM parameter space. An extended scan of the MSSM parameter space was also performed to test the robustness of these limits.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s100520200895
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    Paper (German National Licenses)
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  • 8
    Electronic Resource
    Electronic Resource
    Proton-Antiproton annihilation at 900 MeV/c into $\pi^0\pi^0\pi^0, \pi^0\pi^0\eta$ and $\pi^0\eta\eta$ (2002)
    Springer
    The European physical journal 23 (2002), S. 29-41 
    Details
    ISSN: 1434-6052
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract. The three reactions $\overline{p}p \rightarrow \pi^0\pi^0\pi^0$ , $\pi^0\pi^0\eta$ and $\pi^0\eta\eta$ in proton-antiproton annihilation in flight at 900 MeV/c are used to search for isoscalar $0^{++}$ and $2^{++}$ mesons in the mass range 1000–2000 MeV, in particular the $f_0(1710)$ . The description of both $\pi^0\pi^0\pi^0$ and $\pi^0\eta\eta$ data sets requires an isoscalar tensor resonance decaying into $\pi^0\pi^0$ and $\eta\eta$ with a mass of $(1867\pm46)$ MeV and a width of $(385\pm58)$ MeV. The ratio of partial widths $\Gamma(\eta\eta)/\Gamma(\pi\pi)$ is $0.27 \pm 0.10$ . The analyses of both $\pi^0\pi^0\pi^0$ and $\pi^0\eta\eta$ show no signal for the $f_0(1710)$ . The $\pi^0\eta\eta$ data set shows a strong signal of the $f_2^{\prime}(1525)$ suggesting a large OZI rule violation for tensor meson production in $\overline{p}p$ annihilation. The $\pi^0\pi^0\pi^0$ data set also requires the $f_2(1565)$ . The signal for the $f_2(1810)$ reported by earlier experiments is confirmed neither in $\pi^0\pi^0\pi^0$ nor in $\pi^0\eta\eta$ . The analysis of $\pi^0\pi^0\eta$ leads to an isovector tensor state decaying into $\pi^0\eta$ with a mass of $(1698\pm44)$ MeV and a width of $(265\pm55)$ MeV.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s100520100860
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  • 9
    Electronic Resource
    Electronic Resource
    Particle multiplicity of unbiased gluon jets from $\mathrme^+\mathrme^-$ three-jet events (2002)
    Springer
    The European physical journal 23 (2002), S. 597-613 
    Details
    ISSN: 1434-6052
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract. The charged particle multiplicities of two- and three-jet events from the reaction e $^+$ e $^-$ $\rightarrow$ Z $^0\rightarrow hadrons$ are measured for Z $^0$ decays to light quark (uds) flavors. Using recent theoretical expressions to account for biases from event selection, results corresponding to unbiased gluon jets are extracted over a range of jet energies from about 11 to 30 GeV. We find consistency between these results and direct measurements of unbiased gluon jet multiplicity from $\Upsilon$ and Z $^0$ decays. The unbiased gluon jet data including the direct measurements are compared to corresponding results for quark jets. We perform fits based on analytic expressions for particle multiplicity in jets to determine the ratio $r\equiv\mathrm{N}_{g}/\mathrm{N}_{q}$ of multiplicities between gluon and quark jets as a function of energy. We also determine the ratio of slopes, $r^{(1)}\equiv(\mathrm{d}\mathrm{N}_{g} /\mathrm{d}y) /(\mathrm{d}\mathrm{N}_{q} /\mathrm{d}y)$ , and of curvatures, $r^{(2)}\equiv(\mathrm{d}^2\mathrm{N}_{g} /\mathrm{d}y^2) /(\mathrm{d}^2\mathrm{N}_{q} /\mathrm{d}y^2)$ , where y specifies the energy scale. At 30 GeV, we find $r=1.422\pm0.051,r^{(1)}=1.761\pm0.071$ and $r^{(2)}=1.98\pm0.13$ , where the uncertainties are the statistical and systematic terms added in quadrature. These results are in general agreement with theoretical predictions. In addition, we use the measurements of the energy dependence of ${\mathrm{N}}_{g}$ and ${\mathrm{N}}_{q}$ to determine an effective value of the ratio of QCD color factors, $C_{\mathrm A}/C_{\mathrm F}$ . Our result, $C_{\mathrm A}/C_{\mathrm F}=2.23\pm0.14 $ (total), is consistent with the QCD value of 2.25.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s100520200926
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  • 10
    Electronic Resource
    Electronic Resource
    Measurement of dijet electroproduction at small jet separation (2002)
    Springer
    The European physical journal 24 (2002), S. 33-41 
    Details
    ISSN: 1434-6052
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract. Deep-inelastic scattering data in the range $150 〈 Q^2 〈 35 000 {\rm Ge}^2$ are used to investigate the minimum jet separation necessary to allow accurate description of the rate of dijet production using next-to-leading order perturbative QCD calculations. The required jet separation is found to be small, allowing about 1/3 of DIS data to be classified as dijet, as opposed to approximately 1/10 with more typical jet analyses. A number of precision measurements made using this dijet sample are well described by the calculations. The data are also described by the combination of leading order matrix elements and parton showers, as implemented in the QCD based Monte Carlo model RAPGAP.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s100520100888
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