189 research outputs found

    Measurement of time dependent B(d)0 - anti-B(d)0 mixing

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    The time dependent mixing of Bd0-B̄d0 mesons has been observed by using the correlations between the charge of D* mesons and the weighted mean charge of particles in each hemisphere. From a reconstructed D*± sample corresponding to about 1.7 million hadronic Z0 decays, the mass difference between the two Bd0 mass eigenstates has been measured to be Δm = 0.50±0.12 (stat.) ± 0.06 (syst.) (Latin small letter h with stroke sign)/ps or, converting into eV/c2: Δm = [3.29±0.79 (stat.) ± 0.39 (syst.)] 10-4 eV/c2

    A Measurement of D meson production in Z0 hadronic decays

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    A study of the fragmentation properties of charm and bottom quarks into D mesons is presented. From 263 700 Z0 hadronic decays collected in 1991 with the DELPHI detector at the LEP collider, D0, D+ and D*+ are reconstructed in the modes K-π+, K-π+K+ and D0π+ followed by D0→K-π+, respectively. The fractional decay widths {Mathematical expression} are determined, and first results are presented for the production of D mesons from {Mathematical expression} and {Mathematical expression} events separately. The average energy fraction of D*± in charm quark fragmentation is found to be 〈XE(D*)〉c=0.487± 0.015 (stat)±0.005 (sys.). Assuming that the fraction of Ds and charm-baryons produced at LEP is similar to that around 10 GeV, the Z0 partial width into charm quark pairs is determined to be Γc/Γh=0.187±0.031 (stat)±0.023 (sys). The probability for a b quark to fragment into {Mathematical expression} or b-baryons is inferred to be 0.268±0.094 (stat)±0.100 (sys) from the measured probability that it fragments into a {Mathematical expression} or B-. © 1993 Springer-Verlag.0SCOPUS: ar.jinfo:eu-repo/semantics/publishe

    A Precise measurement of the B(d)0 meson lifetime using a new technique

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    From data recorded by DELPHI between 1991 and 1994, which corresponds to 3.2 million hadronic Z(0) decays, a measurement of the <(B-d(0))over bar> meson lifetime, based on the inclusive reconstruction of 3520 +/- 150 semileptonic decays of the type <(B-d(0))over bar> --> D*+ l <(nu(l))over bar>, has been performed, The result is: tau(B-d(0)) = 1.532 +/- 0.041(stat.) +/- 0.040(syst.)ps. The contribution to the systematic uncertainty which depends on external errors is +/-0.015

    MEASUREMENT OF TIME-DEPENDENT B-D(0) (B)OVER-BAR-D(0) MIXING

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    The time dependent mixing of B-d(0)-(B) over bar(d)(0) mesons has been observed by using the correlations between the charge of D-* mesons and the weighted mean charge of particles in each hemisphere. From a reconstructed D-*+/- sample corresponding to about 1.7 million hadronic Z(0) decays, the mass difference between the two B-d(0) mass eigenstates has been measured to be hm = 0.50 +/- 0.12 (stat.) +/- 0.06 (syst.) (h) over bar/ps or, converting into eV/c(2): Delta m = [3.29 +/- 0.79 (stat.) +/- 0.39 (syst.)] 10(-4) eV/c(2)

    A MEASUREMENT OF B+ AND B-0 LIFETIMES USING (D)OVER-BAR-L(+) EVENTS

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    A measurement of B meson lifetimes is presented using data collected from 1991 to 1993 by the DELPHI detector at the LEP collider, Samples of events with a D meson and a lepton in the same jet are selected where ()overbarD(0)l(+)andD()l(+)eventsoriginatemainlyfromthesemileptonicdecaysofB+andB0mesons,respectively.FromthereconstructedBdecaylengthandtheestimatedBmomentum,takingintoaccountthedilutionduetoBdecaysinto() over bar D(0)l(+) and D*(-)l(+) events originate mainly from the semileptonic decays of B+ and B-0 mesons, respectively. From the reconstructed B decay length and the estimated B momentum, taking into account the dilution due to B decays into () over bar D**l(+)v, the following B meson lifetimes and lifetime ratio are measured: tau(B+) = 1.61(-0.16)(+0.16) (stat.) +/- 0.12 (syst.) ps tau(B-0) = 1.61(-0.13)(+0.14) (stat.) +/- 0.08 (syst.) ps tau (B+)/tau(B-0) = 1.00(-0.15)(+0.17) (stat.) +/- 0.10 (syst.) and an average lifetime of B+ and B-0 mesons is obtained: tau(B) = 1.61(-0.07)(+0.08) (stat.) +/- 0.05 (syst.) p

    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 B-d(0) oscillation frequency using kaons, leptons and jet charge

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    A measurement of the mass difference, Delta m(d), be tween the two physical B-d(0) states has been obtained from the analysis of the impact parameter distribution of a lepton emitted at large transverse momentum (p(t)) relative to the jet axis and from the analysis of the flight distance distribution of secondary vertices tagged by either a high p(t) lepton or an identified kaon. In the opposite hemisphere of the event, the charge of the initial quark has been evaluated using a high p(t) lepton, a charged kaon or the mean jet charge, With 1.7 million hadronic Z(0) decays recorded by DELPHI between 1991 and 1993, Delta m(d) is found to be: Delta m(d) = 0.531 (+0.050)(-0.046) (stat.) +/- 0.078 (syst.) ps(-1)

    Measurement of the forward - backward asymmetry of charm and bottom quarks at the Z pole using D*+- mesons

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    The forward-backward asymmetries for the processes {Mathematical expression} and {Mathematical expression} at the Z resonance are measured using identified D*± mesons. In 905,000 selected hadronic events, taken in 1991 and 1992 with the DEL-PHI detector at LEP, 4757 D*+→D0π+ decays are reconstructed. The c and b quark forward-backward asymmetries are determined to be: {Mathematical expression} Constraining the b asymmetry to the value measured by DELPHI using independent analyses, the charm asymmetry is determined to be: {Mathematical expression}. This result corresponds to an effective electroweak mixing angle measured using charm quark events of: {Mathematical expression} © 1995 Springer-Verlag

    A precise measurement of the B-d(0) meson lifetime using a new technique

    No full text
    From data recorded by DELPHI between 1991 and 1994, which corresponds to 3.2 million hadronic Z0 decays, a measurement of the Bd0 meson lifetime, based on the inclusive reconstruction of 3520 ± 150 semileptonic decays of the type Bd0 → D*+ X ℓ νℓ, has been performed. The result is: τ(Bd0) = 1.532 ± 0.041(stat.) ± 0.040(syst.)ps. The contribution to the systematic uncertainty which depends on external errors is ±0.015. © Springer-Verlag 1997

    A precise measurement of the B-d(0) meson lifetime using a new technique

    No full text
    From data recorded by DELPHI between 1991 and 1994, which corresponds to 3.2 million hadronic Z(0) decays, a measurement of the <(B-d(0))over bar> meson lifetime, based on the inclusive reconstruction of 3520 +/- 150 semileptonic decays of the type <(B-d(0))over bar> –> D*+ l <(nu(l))over bar>, has been performed, The result is: tau(B-d(0)) = 1.532 +/- 0.041(stat.) +/- 0.040(syst.)ps. The contribution to the systematic uncertainty which depends on external errors is +/-0.015
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