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  • 2000-2004  (24)
  • 2002  (24)
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  • 2000-2004  (24)
Year
  • 1
    Electronic Resource
    Electronic Resource
    Transverse mass distributions of neutral pions from $^{208}$ Pb-induced reactions at 158 $\cdot A$ GeV (2002)
    Springer
    The European physical journal 23 (2002), S. 225-236 
    Details
    ISSN: 1434-6052
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract. Results on transverse mass spectra of neutral pions measured at central rapidity are presented for impact parameter selected 158 $\cdot A$ GeV Pb + Pb, and Pb + Nb collisions. The distributions cover the range $0.5 \mathrm{GeV}/c^2 \le m_T - m_0 \le 4 \mathrm{GeV}/c^2$ . The change of the spectral shape and the multiplicity with centrality is studied in detail. In going from p+p to semi-peripheral Pb+Pb collisions there is a nuclear enhancement increasing with transverse mass similar to the well known Cronin effect, while for very central collisions this enhancement appears to be weaker than expected.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s100520100886
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    Paper (German National Licenses)
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  • 2
    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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    Paper (German National Licenses)
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  • 3
    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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  • 4
    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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    Paper (German National Licenses)
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  • 5
    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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    Paper (German National Licenses)
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  • 6
    Electronic Resource
    Electronic Resource
    Dijet photoproduction at HERA and the structure of the photon (2002)
    Springer
    The European physical journal 23 (2002), S. 615-631 
    Details
    ISSN: 1434-6052
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract. The dijet cross section in photoproduction has been measured with the ZEUS detector at HERA using an integrated luminosity of 38.6 pb $^{-1}$ . The events were required to have a virtuality of the incoming photon, $Q^2$ , of less than 1 GeV $^2$ and a photon-proton centre-of-mass energy in the range $134 〈 W_{\gamma p} 〈 277$ GeV. Each event contains at least two jets satisfying transverse-energy requirements of $E_{T}^{\rm jet1}〉14$ GeV and $E_{T}^{\rm jet2}〉11$ GeV and pseudorapidity requirements of \mbox{ $-1〈\eta^{\rm jet1,2}〈2.4$ }. The measurements are compared to next-to-leading-order QCD predictions. The data show particular sensitivity to the density of partons in the photon, allowing the validity of the current parameterisations to be tested.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s100520200936
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    Paper (German National Licenses)
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  • 7
    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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  • 8
    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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    Paper (German National Licenses)
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  • 9
    Electronic Resource
    Electronic Resource
    Measurement of the hadronic cross-section for the scattering of two virtual photons at LEP (2002)
    Springer
    The European physical journal 24 (2002), S. 17-31 
    Details
    ISSN: 1434-6052
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract. The interaction of virtual photons is investigated using the reaction ${\rm e^+e^-} \rightarrow{\rm e^+e^-}$ hadrons based on data taken by the OPAL experiment at ${\rm e^+e^-}$ centre-of-mass energies $\sqrt{s_{\rm ee}}=189-209$ GeV, for $W〉5$ GeV and at an average $Q^{2}$ of 17.9 GeV $^2$ . The measured cross-sections are compared to predictions of the Quark Parton Model (QPM), to the Leading Order QCD Monte Carlo model PHOJET, to the NLO prediction for the reaction ${\rm e^+e^-}\rightarrow{\rm e^+e^-} q\bar{q}$ , and to BFKL calculations. PHOJET, NLO ${\rm e^+e^-}\rightarrow{\rm e^+e^-} q\bar{q}$ , and QPM describe the data reasonably well, whereas the cross-section predicted by a Leading Order BFKL calculation is too large.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s100520200940
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    Paper (German National Licenses)
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  • 10
    Electronic Resource
    Electronic Resource
    Investigation of the decay of orbitally-excited B mesons and first measurement of the branching ratio ${\rm BR}({\rm B}^*_J \rightarrow{\rm B}^* \pi (X))$ (2002)
    Springer
    The European physical journal 23 (2002), S. 437-454 
    Details
    ISSN: 1434-6052
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract. From about 4 million hadronic $\rm Z^0$ decays recorded by the OPAL detector on and near to the $\rm Z^0$ resonance, we select a sample of more than 570 000 inclusively reconstructed B mesons. Orbitally-excited mesons ${\rm B}^*_J$ are reconstructed using ${\rm B}\pi^\pm$ combinations. Independently, ${\rm B}^*$ mesons are reconstructed using the decay ${\rm B}^*\rightarrow{\rm B}{\gamma} $. The selected $ {\rm B}^*$ candidates are used to obtain samples enriched or depleted in the decay ${\rm B}^*_J \rightarrow{\rm B}^* \pi^{\pm}(X)$ , where (X) refers to decay modes with or without additional accompanying decay particles. From the number of signal candidates in the ${\rm B}\pi^\pm$ mass spectra of these two samples, we perform the first measurement of the branching ratio of orbitally-excited B mesons decaying into ${\rm B}^*\pi(X)$ : $$ {\rm BR}( {\rm B}^*_J \rightarrow{\rm B}^* \pi (X)) = 0.85^{ +0.26}_{ -0.27} \pm 0.12 ,$$ where the first error is statistical and the second systematic.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s100520200892
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    Paper (German National Licenses)
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