54 research outputs found

    Determination of vertical bar V-cb vertical bar from the semileptonic decay B-0->D*(-)l(+)nu

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    Determination of the average lifetime of b-baryons

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    The average lifetime of b-baryons has been studied using 3 × 106 hadronic Z0 decays collected by the DEL-PHI detector at LEP. Three methods have been used, based on the measurement of different observables: the proper decay time distribution of 206 vertices reconstructed with a Λ, a lepton and an oppositely charged pion; the impact parameter distribution of 441 muons with high transverse momentum accompanied by a Λ in the same jet; and the proper decay time distribution of 125 Λc-lepton decay vertices with the Λc exclusively reconstructed through its pKπ, pK0 and Λ3π decay modes. The combined result is: τ(b-baryon) = (1.254-0.109+0.121(stat) ±0.04(syst)-0.05+0.03(syst)) ps where the first systematic error is due to experimental uncertainties and the second to the uncertainties in the modelling of the b-baryon production and semi-leptonic decay. Including the measurement recently published by DELPHI based on a sample of proton-muon vertices, the average b-baryon lifetime is : τ(b-baryon) = (1.255-0.102+0.115(stat) ±0.05) ps. © Springer-Verlag 1996

    Production of Sigma(0) and Omega(-) in Z decays

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    Reconstructed \lam\ baryon decays and photon conversions in DELPHI are used to measure the \sig\ production rate from hadronic Z^0 decays at LEP. The number of \sig\ decays per hadronic Z decay is found to be: \begin{center} \sig + \sigb = \wffe{0.070}{0.010}{0.010 }{}. \end{center} \bigskip The \Omega^- production rate is similarly measured to be: \begin{center} \Omega^- + \overline{\Omega}^+ = \wffe{0.0014}{0.0002}{0.0004}

    Search for exclusive decays of the Lambda(b) baryon and measurement of its mass

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    A search for fully reconstructed Lambda(b)(0) beauty baryons is performed using about 3 million Z decays collected with the DELPHI detector at LEP. The analysis relies on the combined use of the accurate tracking and of the hadron identification capabilities of DELPHI. A total of four events has been found, three in the Lambda(c)(+)pi(-) channel and one in the Lambda(c)(+)a(1)(-) channel over a small background. The Lambda(b)(0) beauty baryon mass is measured to be (5668 +/- 16 (stat.) +/-8 (syst.)) MeV/c(2)

    Determination of vertical bar V-cb vertical bar from the semileptonic decay B-0->D*(-)l(+)nu

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    Semileptonic decays B --> D*(-)l(+)nu X were selected from a sample of 3.1 million hadronic Z decays collected by the DELPHI detector at LEP. A topological search for semileptonic B decays to resonant and non-resonant D*(-)pi(+) states was performed and the ratio of the branching fractions: Br(B --> D*(-)l(+)nu X)/Br(B --> D*(-)l(+)nu X) + Br(B-0 --> D*(-)l(+)nu) = 0.19 +/- 0.10(stat) +/- 0.06(syst) was determined. Taking into account this contribution, the differential decay width of B-0 --> D*(-)l(+)nu was measured as a function of the momentum transfer from the B to the D*(-) in two separate analyses, using exclusive and inclusive methods of D*(-) reconstruction. The distributions were fitted over the full momentum transfer range to extract the product of /V-cb/ times the normalization of the decay form factor F(q(max)(2)): F(q(max)(2))/V-cb/ = (35.4 +/- 1.9(stat) +/- 2.4(syst)) . 10(-3). The value of /V-cb/ was computed using theoretical calculations of F(q(max?2), giving: /V-cb/ = (38.9 +/- 2.0(stat) +/- 2.6(syst) +/- 1.7(theory)) . 10(-3). The total branching fraction Br(B-0 --> D*(-)l(-)nu) was determined to be: Br(B-0 --> D*(-)l(+)nu) = (5.52 +/- 0.17(stat) +/- 0.68(syst))%

    Measurement of the partial decay width R(b)(0)=Gamma(b(b)over-bar)/Gamma(had) of the Z with the DELPHI detector at LEP

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    The partial decay width of the Z to quark pairs has been measured by the DELPHI detector at LEP. B-hadrons, containing b-quarks, were tagged by several methods using tracks with large impact parameters to the primary vertex complemented sometimes by event shape variables or using leptons with high transverse momentum relative to the hadron. In order to reduce the systematic uncertainties, in all methods the b-tagging efficiency has been extracted directly from the data. Combining all methods, the value: Gamma()/Gamma(had) = 0.2216 +/- 0.0016(stat.) +/- 0.0021(syst.) was found, where the production fraction was fixed to its Standard Model value

    Kaon interference in the hadronic decays of the Z(0)

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