Showing papers by "Tohru Takeshita published in 1991"
TL;DR: In this article, the authors show the context of analysis and the first results of a research on media temporalities of the elderly, showing that the global relation of the autonomous elderly persons to the media can evolve when confronted to their new temporal framework and the new program offer, whereas their representations and use of the media remain quite stable.
146 citations
TL;DR: A search for the minimal standard model Higgs boson (H 0 ) has been performed with data from e + e − collisions in the OPAL detector at LEP.
83 citations
TL;DR: In this article, an improved measurement of the mass of the Z0 boson, its total width and its partial decay widths into hadrons and leptons, as well as the effective axial vector and vector couplings to charge lepton was presented.
Abstract: We report on an improved measurement of the mass of theZ0 boson, its total width and its partial decay widths into hadrons and leptons, as well as the effective axial vector and vector couplings to charged leptons. These measurements are based on a data set of approximately 160 000 hadronicZ0 decays and 18 000 decays into electrons, muons and taus, recorded by the OPAL experiment at centre of mass energies near the mass of theZ0. The total width and the partial widths to visible final states, derived from the measured cross sections, are used to extract the invisible width. The effective couplings of theZ0 to charged leptons are studied using measurements of the lepton pair cross sections and forward-backward asymmetries at the different centre of mass energy points of theZ0 scan. The implications of our results in the context of the Standard Model are discussed.
66 citations
TL;DR: The cross section of the pure QED process e + e − → γγ has been measured using data accumulated during the 1989 and 1990 scans of the Z 0 resonance at LEP as discussed by the authors.
66 citations
TL;DR: In this paper, Bose-Einstein correlations between like-sign charged track pairs have been studied in e + e − annihilation hadronic events at centre-of-mass energies around the Z 0 peak as a function of Q, the four-momentum difference of the pair.
63 citations
TL;DR: In this article, the average τ polarization at the Z° resonance is measured to be −0.22 ± 0.04 and a value for the weak mixing angle of sin 2 θ W = 0.07.
58 citations
TL;DR: In this article, four different recombination schemes to define resolvable jets were compared and the strong coupling constant αs(M_{Z^0 } ) was determined in fits of the corresponding O(αs2) QCD calculations to the differential 2-jet distributions.
Abstract: Jet production rates in hadronicZ0 decays are studied using four different recombination schemes to define resolvable jets. The strong coupling constant αs(\(M_{Z^0 } \)) is determined in fits of the correspondingO(αs2) QCD calculations to the differential 2-jet distributionsD2(y). Hadronisation corrections and renormalisation scale uncertainties are found to be different for each recombination scheme. Within their overall systematic uncertainties, the four schemes yield consistent values of αs(\(M_{Z^0 } \)), leading to a final result of
$$\alpha _s (M_{Z^0 } ) = 0.118 \pm 0.008.$$
.
52 citations
TL;DR: In this article, a symmetry under transposition of the energies and directions of a quark and gluon jet was selected for e+e−three-jet events at LEP using lepton tagging of quark jets through observation of semi-leptonic charm and bottom quark decays.
48 citations
TL;DR: In this paper, the authors investigated the production of K0 mesons in e+e− interactions at center of mass energies in the region of the Z0 mass with the OPAL detector at LEP.
45 citations
TL;DR: In this paper, the authors measured the fraction of events containing semi-leptonic decays of b flavoured hadrons using the shape of the momentum and transverse momentum distributions of the muon candidates.
40 citations
TL;DR: In this article, the authors used the semi-leptonic decays of charm and bottom quarks to identify quarks and gluons in 3-jet events from hadronic Z0 decays.
TL;DR: In this paper, the existence of a minimal supersymmetric standard model with mass in the range 0 ⩽ m H ⌽ 11.3 GeV/c 2 is excluded at the 95% confidence level for all possible decay modes of the H 0.
TL;DR: In this paper, a factorial moment analysis has been performed on the differential multiplicity distributions of hadronic final states of the Z 0 recorded with the OPAL detector at LEP.
TL;DR: In this article, an investigation of the production of D ∗ ± mesons produced in e + e − collisions at energies around the Z 0 pole is presented, and the properties of D∗ mesons generated in the reaction Z 0 → c c c are studied.
TL;DR: In this paper, the production rate of final state photons in hadronic Z0 decays is measured as a function of ycut = Mij2/Ecm2 the jet resolution parameter and minimum mass of the photon-jet system.
TL;DR: In this paper, the authors measured the photon yield in lepton pair events recorded by the OPAL detector in a data sample corresponding to an integrated luminosity of 7.1 pb−1 at centre-of-mass energies between 88 GeV and 94 GeV.
TL;DR: In this paper, a sample of approximately 45 reconstructed J ψ mesons was measured to be Br(Z0→J/ψ + X) = (4.5±0.8± 0.6) × 10−3, where the first error is statistical, the second systematic, and the third error is due to the uncertainty in the leptonic decay rate of the Jψ.
TL;DR: In this article, the four-jet final states of hadronicZ0 decays, observed ine+e− annihilation around 91 GeV center of mass energy, are analyzed in terms of observables that are sensitive to the non-abelian gauge structure of QCD.
Abstract: Four-jet final states of hadronicZ0 decays, observed ine+e− annihilation around 91 GeV centre of mass energy, are analysed in terms of observables that are sensitive to the non-abelian gauge structure of QCD. After correction for detector resolution and fragmentation effects, the data are compared to QCD and also to predictions of the Abelian vector gluon gauge theory. The theoretical expectations are calculated in both second order and leading logarithmic approximation of perturbation theory. The data are compatible with QCD but cannot be described by the predictions of the Abelian vector gluon models. From the measured topological distributions, upper limits for the relative production rates of\(q\bar qq\bar q\) final states are derived.
TL;DR: In this article, a search for minimal standard model (MSM) and minimal supersymmetric model (MSSM), Higgs bosons with masses larger than 3 GeV/c2 has been performed by the OPAL collaboration one+e− data from LEP corresponding to an integrated luminosity of 1.24 pb−1.5 GeV /c2.
Abstract: A search for minimal standard model (MSM) and minimal supersymmetric model (MSSM), Higgs bosons with masses larger than 3 GeV/c2 has been performed by the OPAL collaboration one+e− data from LEP corresponding to an integrated luminosity of 1.24 pb−1. The limits for MSM Higgs bosons have been obtained using the channelsZ0→Z0*H0,Z0*→(v\(\bar v\) ore+e− or µ+, µ−. The search for MSSM Higgs bosons has been performed using the channelsZ0→Z0*H0,v\(\bar v\) ore+e− or µ+µ−),h0 →q\(\bar q\) andZ0→h0A0,h0A0→(4 jet orτ+τ−→ or 4τ), whereh0 andA0 are the two lightest neutral MSSM Higgs bosons. No Higgs boson signal has been observed. The MSM Higgs boson is excluded in the mass range 3 GeV <\(m_{H^0 }\)<25.3 GeV/c2 at the 95% confidence level; limits on the masses of the two lightest neutral MSSM Higgs bosons are obtained forh0 mases up to 40.5 GeV/c2.
TL;DR: In this article, a search for lepton flavour violation through the decays Z0 → eμ, eτ and μτ was made with the DELPHI detector at LEP, using a sample corresponding to an integrated luminosity of 11.2 pb−1.
TL;DR: In this paper, the OPAL detector at LEP is used to measure the branching ratio of the Z0 into invisible particles by measuring the cross section of single photon events ine+e− collisions at centre-of-mass energies near theZ0 resonance.
Abstract: The OPAL detector at LEP is used to measure the branching ratio of theZ0 into invisible particles by measuring the cross section of single photon events ine+e− collisions at centre-of-mass energies near theZ0 resonance. In a data sample of 5.3 pb−1, we observe 73 events with single photons depositing more than 1.5 GeV in the electromagnetic calorimeter, with an expected background of 8±2 events not associated with invisibleZ0 decay. With this data we determine theZ0 invisible width to be 0.50±0.07±0.03 GeV, where the first error is statistical and the second systematic. This corresponds to 3.0±0.4±0.2 light neutrino generations in the Standard Model.
TL;DR: In this article, the Bose-Einstein correlation for pairs of like signed pions was observed and 95% CL upper limits for the cross-sectionσ(γγ→ρ€€ 0.5€ 2π€ 3π€ 1€ 2€ 6€ 0€ 3€ 1 € 2€ 3 € 3€ 2 € 3π € 3 € 2 € 6€ 3 ρ+3π€ 4€ 1.
Abstract: The reactionγγ→3π
+3π
- has been studied usig the JADE detector at PETRA The topological cross sectionσ(γγ→3π
+3π
-) was measured in the CM energy range 15–55 GeV The production ofρ
0,s was observed and the average number ofρ
0,s per event measured The contributions of the subprocessesγγ→ρ
02π
+2π
-,γγ→ρ
0
ρ
0
π
+2π
- andγγ→ 3π
+3π
- (phase space) were studied and 95% CL upper limits for the cross sectionσ(γγ→ρ
0
ρ
0
π
+
π
- determined Finally the Bose-Einstein correlation for pairs of like signed pions was observed A fit to a standard parametrization gave results consistent with other studies of this effect in pion systems
TL;DR: In this article, three jet variables constructed from multi-hadronic events produced by Z0 decays are compared to theoretical calculations assuming a vector gluon or a hypothetical scalar gluons.
Abstract: Three-jet variables constructed from multi-hadronic events produced byZ0 decays are compared to theoretical calculations assuming a vector gluon or a hypothetical scalar gluon. The data yield conclusive direct evidence for the former case. The distributions of the reduced energy of the second-most energetic jet and of the cosine of the Ellis-Karliner angle are chosen to demonstrate this effect.