116 research outputs found

    J / psi production in the hadronic decays of the Z

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    J/ψ mesons have been reconstructed from their decay to μ+μ- and e+e-, using the data collected by the DELPHI experiment during 1991 and 1992 at the LEP collider. From about 1 million hadronic Z decays 153 ± 17 J/ψ were found, 5.4 ± 2.3 ψ′ were obtained in the channel J/ψ (→μ+μ-)π+π- and 6.4 ± 2.7 χc in the channel J/ψ ( → μ+μ-)γ. As the dominant source of Jψ mesons is from bquarks, the following branching ratios: Br(b → J/ψ X) = (1.12 ± 0.12 (stat) ± 0.10 (syst.))%, Br(b → ψ′ X) = (0.48 ± 0.22 (stat.± 0.10 (syst.))%, Br(b → χc1 X) = (1.4 ± 0.6 (stat.)-0.2+0.4 (syst.))% were measured. From the proper time distribution of the J/ψ sample, the average lifetime of b-hadrons decaying into J/ψ was found to be: τB = 1.50-0.21+0.24 (stat.) ± 0.03 (syst.) ps. A search for completely reconstructed B meson decays to final states including a J/ψ gave a signal of 15 ± 5 events.0info:eu-repo/semantics/publishe

    J/PSI-PRODUCTION IN THE HADRONIC DECAYS OF THE Z

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    J/psi mesons have been reconstructed from their decay to mu(+)mu(-) and e(+)e(-), using the data collected by the DELPHI experiment during 1991 and 1992 at the LEP collider. From about 1 million hadronic Z decays 153 +/- 17 J/psi were found, 5.4 +/- 2.3 psi’ were obtained in the channel J/psi(–> mu(+)mu(-))pi(+)pi(-) and 6.4 +/- 2.7 chi(c) in the channel J/psi(–> mu(+)mu(-))gamma. As the dominant source of J/psi mesons is from b quarks, the following branching ratios: Br(b–>J/psi X) = (1.12 +/- 0.12 (stat.) +/- 0.10 (syst.))%, Br(b –> psi’ X) = (0.48 +/- 0.22 (stat.) +/- 0.10 (syst.))%, Br(b–>chi(cl) X) = (1.4 +/- 0.6 (stat.)(-0.2)(+0.4) (syst.))% were measured. From the proper time distribution of the J/psi sample, the average lifetime of b-hadrons decaying into J/psi was found to be: tau(B) = 1.50(-0.21)(+0.24) (stat.) +/- 0.03 (syst.) ps. A search for completely reconstructed B meson decays to final states including a J/psi gave a signal of 15 +/- 5 events

    A Measurement of the B(s)0 meson mass

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    Strange beauty meson Bs0 have been reconstructed through exclusive hadronic final states, using the data collected in 1992 by the DELPHI experiment at the LEP collider. The analysis relies on the combined use of accurate tracking and of the hadron identification capabilities of DELPHI. Three Bs0 decay candidates have been selected over a negligible background using theDs- π+, Ds- a1+ (1260) and J Ψ φ decay modes, with identified kaons in the final state. The Bs0 meson mass is measured to be mBs = (5374± 16± 2) MeV/ c2. © 1994.0SCOPUS: ar.jinfo:eu-repo/semantics/publishe

    Invariant mass dependence of particle correlations in hadronic final states from the decay of the Z0

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    Two-particle correlations in invariant mass are studied separately for like-sign and unlike-sign pions. Strong correlations are observed only at small masses. The correlations decrease very rapidly for like-sign pions and slowly for unlike-sign pions, manifesting different particle dynamics. The like-sign correlations exhibit a power-law behaviour as a function of mass, compatible with the previously observed intermittency effect. The predictions of the parton shower model (JETSET 7.3) deviate significantly from the data. However, good agreement is obtained with the mass correlations, both for the unlike-sign and for the like-sign pairs if the production of the η′ and ρ0 mesons is reduced and Bose-Einstein correlations are included in the model. The value of the Bose-Einstein correlation strength is consistent with unity for pions which are produced directly or in the decays of short-lived resonances. © 1994 Springer-Verlag.0SCOPUS: ar.jinfo:eu-repo/semantics/publishe

    First Measurement of the Strange Quark Asymmetry at the Z0 Peak

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    A measurement of the strange quark forward-backward asymmetry at the Z0 peak was performed using 718,000 multihadronic Z0 decays collected by the DELPHI detector at LEP in 1992. The s-quark was tagged by the presence of high momentum charged kaons identified by the Ring Imaging Cherenkov detector and by Λ0;s decaying into pπ-. The s-quark purity obtained was estimated for the two hadrons to be 43%. The average s-quark asymmetry was found to be 0.131±0.035 (stat.) ±0.013 (syst.). The forward-backward asymmetry was measured for unresolved d-and s-quarks, tagged by the detection of a high energy neutron or neutral kaon in the Hadron Calorimeter. The combined d-and s-quark purity was 69% and their asymmetry was found to be 0.112±0.031 (stat.) ±0.054 (syst.). © 1995 Springer-Verlag.0SCOPUS: ar.jinfo:eu-repo/semantics/publishe

    Production rate and decay lifetime measurements of B(s)0 mesons at LEP using D(s) and phi mesons

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    The study of the properties of inclusive production of Ds mesons and of events in which a φ{symbol} and a muon are present in the same jet provides two independent measurements of the probability, fs w, for a heavy quark to hadronize into a strange B or D meson. The data sample analysed corresponds to 243,000 hadronic Z0 decays. The combined value of these measurements is fs w=0.19±0.06±0.08. From the flight distance distributions of Ds and of (φ{symbol}-lepton) secondary vertices, with the lepton emitted at high transverse momentum relative to the jet axis, two values are obtained for the Bs 0 meson lifetime. Combining these measurements with a previous result based on the study of Ds-μ events, the Bs 0 meson lifetime is measured to be: 0.96±0.37 ps. © 1994 Springer-Verlag

    Measurement of Gamma (b anti-b) / Gamma (hadrons) using impact parameter measurements and lepton identification

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    The partial decay width of the Z to {Mathematical expression} quark pairs has been measured by the DELPHI detector at LEP. b-hadrons, containing b-quarks, were tagged by leptons with high transverse momentum relative to the hadron or by tracks with large impact parameters to the primary vertex. The ratio of the numbers of events with a single such tag to those with two tags was used to estimate the efficiency of the method and to reduce the systematic uncertainty. Combining all methods, the value: {Mathematical expression} was found, where the third error corresponds to a±8% uncertainty on the {Mathematical expression} production width. A maximum likelihood in to the single and di-lepton distributions gave the branching fraction of the decays of b-quarks to leptons as: {Mathematical expression} © 1995 Springer-Verlag.0SCOPUS: ar.jinfo:eu-repo/semantics/publishe
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