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    172 research outputs found

    ”A HYBRID STANDING WAVE TRAVELING-WAVE PHOTOINJECTOR”

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    Archivio della ricerca- Università di Roma La Sapienza

    Improved measurement of the B(d)0 - anti-B(d)0 oscillation frequency

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    The time dependence of Bd0−−Bˉd0B^0_d--\bar{B}^0_d oscillations is measured by the ALEPH experiment at LEP, using three techniques, two of which are updates of previous measurements. In all cases the charge of the decaying bb quark and its decay time are measured in one hemisphere of the event; the quark charge at production is tagged mainly using the opposite hemisphere. The first method uses the charge correlation between a D∗−D^{*-} and a lepton in the opposite hemisphere; if no lepton is present, the produced quark charge is determined from the hemisphere charges. In the second method, the decay time is measured using a lepton in one hemisphere and the initial state is inferred from the opposite-hemisphere jet charge. The third method uses a lepton in each hemisphere. The data used were collected from 1991 to 1994. The combined result is $\Delta m_d = 0.436\pm 0.033\, {\rm ps}^{-1}
    Crossref
    Politecnio die Bari - Catalogo di prodotti della Ricerca
    Archivio della Ricerca - Università degli Studi di Siena
    AIR Universita degli studi di Milano
    Archivio istituzionale della Ricerca - Scuola Normale Superiore
    Archivio della Ricerca - Università di Pisa
    Copenhagen University Research Information System
    CINECA IRIS Institutial research information system UNISS
    ePubs: the open archive for STFC research publications
    CERN Document Server

    Measurement of D(s)+ meson production in Z decays and of the anti-B(s)0 lifetime

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    D(s)+ mesons produced in Z(0) --> b (b) over bar events were separated from the Z(0) --> c (c) over bar component using a lifetime tag. Using a sample of 1.5 million hadronic Z decays collected with the ALEPH detector the (B) over bar(s)(0) and Ds(+) yields have been measured.The (B) over bar (s)(0) lifetime was measured in a anti B(s)(0) enriched sample reconstructing the decay length from the vertex of the D(s)+ with a hadron from the (B) over bar (s)(0) decay, The result obtained is: tau_B(s) =(1.61 + (+0.30 -0.29)(stat.) + (+0.18-0.16) (syst.)) ps
    Crossref
    Politecnio die Bari - Catalogo di prodotti della Ricerca
    Archivio della Ricerca - Università degli Studi di Siena
    AIR Universita degli studi di Milano
    Archivio istituzionale della Ricerca - Scuola Normale Superiore
    Archivio della Ricerca - Università di Pisa
    Archivio istituzionale della ricerca - Università di Bari
    Copenhagen University Research Information System
    CINECA IRIS Institutial research information system UNISS
    ePubs: the open archive for STFC research publications

    A Measurement of the |V(cb)| from anti-B(0) --> D*+- lepton- anti-lepton-neutrino

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    From approximately 3 million hadronic decays of Z bosons recorded with the ALEPH detector at LEP, a sample of 410 +/- 32 B0bar -> D*+ l- nubar candidates is selected, where l- is either an electron or a muon. The differential decay rate dGamma(B0bar -> D*+ l- nubar)/dw from this sample is fitted, yielding a value for the product of the CKM matrix element |Vcb| and the normalisation of the decay form factor at the point of zero recoil of the D*+ meson: F(w=1)|Vcb| = [31.4 +/-2.3(stat.) +/-2.5(syst.)] #users.txt# DistList LAforwarding PSforwarding batch done errors files helpND.html images insert_new.sh instlog log modifying pending pending.bk running stats users.txt users.txt~ waiting 10^(-3). A value for |Vcb| is extracted using theoretical calculations of the form factor normalisation, with the result: |Vcb| = [34.5 +/-2.5(stat.) +/-2.7(syst.) +/-1.5(theory)] #users.txt# DistList LAforwarding PSforwarding batch done errors files helpND.html images insert_new.sh instlog log modifying pending pending.bk running stats users.txt users.txt~ waiting 10^(-3). From the integrated spectrum, the measured branching fraction is Br(B0bar -> D*+ l- nubar) = 5.18 +/-0.30(stat.) +/-0.62(syst.)%
    Institutional Knowledge at Singapore Management University
    Archivio istituzionale della ricerca - Università di Bari
    CINECA IRIS Institutial research information system UNISS
    ePubs: the open archive for STFC research publications
    Archivio istituzionale della ricerca - Università di Trieste
    Crossref
    Politecnio die Bari - Catalogo di prodotti della Ricerca
    Archivio della Ricerca - Università degli Studi di Siena
    AIR Universita degli studi di Milano
    Archivio istituzionale della Ricerca - Scuola Normale Superiore
    Archivio della Ricerca - Università di Pisa
    Copenhagen University Research Information System
    CERN Document Server

    Measurement of the effective b quark fragmentation function at the Z resonance

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    Using a sample of about 1.46 million hadronic Z decays collected between 1991 and 1993 with the ALEPH detector at LEP, the energy distribution of the B0 and B± mesons produced at the Z resonance is measured by reconstructing semileptonic decays B → ℓνℓD(X) or . The charmed mesons are reconstructed through the decay modes D0 → K−π+, D0 → K−π+π−π+, D+ → K−π+π+ and . The neutrino energy is estimated from the missing energy in the lepton hemisphere. Accounting for B∗ and B∗∗ production, the shape of the scaled energy distribution xE(b) for mesons containing a b quark is compared to the predictions of different fragmentation models. The mean value of xE(b) is found to be 〈xE(b)〉 = 0.715 ± 0.007(stat) ± 0.013(syst)
    Hal - Université Grenoble Alpes
    HAL AMU
    Institutional Knowledge at Singapore Management University
    HAL Clermont Université
    Archivio istituzionale della ricerca - Università di Bari
    HAL Université de Savoie
    CINECA IRIS Institutial research information system UNISS
    ePubs: the open archive for STFC research publications
    Archivio istituzionale della ricerca - Università di Trieste
    HAL-IN2P3
    Crossref
    Politecnio die Bari - Catalogo di prodotti della Ricerca
    Archivio della Ricerca - Università degli Studi di Siena
    AIR Universita degli studi di Milano
    Archivio istituzionale della Ricerca - Scuola Normale Superiore
    Archivio della Ricerca - Università di Pisa
    Copenhagen University Research Information System
    Lancaster E-Prints
    CERN Document Server

    Charm counting in b decays

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    The inclusive production of charmed particles in decays has been measured from the yield of D0, D+, Ds+ and Λc+ decays in a sample of events with high b purity collected with the ALEPH detector from 1992 to 1995. From these measurements, adding the charmonia production rate and an estimate of the charmed strange baryon contribution, the average number of charm quarks per b decay is determined to be nc = 1.230 ± 0.036 ± 0.038 ± 0.053, where the uncertainties are due to statistics, systematic effects and branching ratios, respectively
    Hal - Université Grenoble Alpes
    HAL AMU
    HAL Clermont Université
    Archivio istituzionale della ricerca - Università di Bari
    HAL Université de Savoie
    CINECA IRIS Institutial research information system UNISS
    ePubs: the open archive for STFC research publications
    Archivio istituzionale della ricerca - Università di Trieste
    HAL-IN2P3
    Crossref
    Politecnio die Bari - Catalogo di prodotti della Ricerca
    Archivio della Ricerca - Università degli Studi di Siena
    AIR Universita degli studi di Milano
    Archivio istituzionale della Ricerca - Scuola Normale Superiore
    Archivio della Ricerca - Università di Pisa
    Copenhagen University Research Information System
    Lancaster E-Prints
    CERN Document Server
    HAL-Polytechnique

    Measurements of the b baryon lifetime

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    Using about 1.5 million hadronic Z decays recorded with the aleph detector, the lifetime of the b baryons has been measured using two independent data samples. From a maximum likelihood fit to the impact parameter distribution of leptons in 519 Λℓ− combinations containing a b baryon sample of 290 decays, the measured b baryon lifetime is τb—baryon = 1.05−0.11+0.12(stat)±0.09(syst) ps. The lifetime of the Λb0 baryon from a maximum likelihood fit to the proper time distribution of 58 Λc+ℓ− candidates containing a Λb0 sample of 44 decays, is τΛb0 = 1.02−0.18+0.23(stat) ± 0.06(syst) ps
    Hal - Université Grenoble Alpes
    HAL AMU
    Institutional Knowledge at Singapore Management University
    HAL Clermont Université
    Archivio istituzionale della ricerca - Università di Bari
    HAL Université de Savoie
    CINECA IRIS Institutial research information system UNISS
    ePubs: the open archive for STFC research publications
    Archivio istituzionale della ricerca - Università di Trieste
    HAL-IN2P3
    Politecnio die Bari - Catalogo di prodotti della Ricerca
    Archivio della Ricerca - Università degli Studi di Siena
    AIR Universita degli studi di Milano
    Archivio istituzionale della Ricerca - Scuola Normale Superiore
    Archivio della Ricerca - Università di Pisa
    Copenhagen University Research Information System
    Lancaster E-Prints
    CERN Document Server
    HAL-Polytechnique

    Study of the fragmentation of b quarks into B mesons at the Z peak

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    The fragmentation of b quarks into B mesons is studied with four million hadronic Z decays collected by the ALEPH experiment during the years 1991–1995. A semi-exclusive reconstruction of B→ℓνD(★) decays is performed, by combining lepton candidates with fully reconstructed D(★) mesons while the neutrino energy is estimated from the missing energy of the event. The mean value of xBwd, the energy of the weakly-decaying B meson normalised to the beam energy, is found to be using a model-independent method; the corresponding value for the energy of the leading B meson is . The reconstructed spectra are compared with different fragmentation models
    Hal - Université Grenoble Alpes
    HAL AMU
    HAL Clermont Université
    Archivio istituzionale della ricerca - Università di Bari
    Publikationsserver der RWTH Aachen University
    HAL Université de Savoie
    Enlighten
    ePubs: the open archive for STFC research publications
    Hal-Diderot
    HAL-IN2P3
    Crossref
    Politecnio die Bari - Catalogo di prodotti della Ricerca
    AIR Universita degli studi di Milano
    Archivio istituzionale della Ricerca - Scuola Normale Superiore
    Archivio della Ricerca - Università di Pisa
    Lancaster E-Prints
    CERN Document Server
    HAL-Polytechnique

    Production of orbitally excited charm mesons in semileptonic B decays

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    A sample of 3.6 million hadronic Z decays recorded between 1991 and 1995 with the ALEPH detector at LEP is used to investigate semileptonic decays of B mesons into final states involving orbitally excited charm mesons. Topological vertex criteria are used to search for decays involving narrow D∗∗^{**} states as well as wide D∗∗^{**} resonances and non-resonant D(∗)π^{(*)}\pi final states. The sum of the branching ratios for these processes is measured to be \begin{eqnarray*} \lefteqn{{\mathrm{Br}}({\overline {\mathrm{B}}} \to {\mathrm{D}}\pi\ell^-\overline\nu) +{\mathrm{Br}}({\overline {\mathrm{B}}} \to {\mathrm{D}}^*\pi\ell^-\overline\nu)}\\ & & = (2.26\pm 0.29(\mathrm{stat}) \pm 0.33(\mathrm{syst}))\%, \end{eqnarray*} which accounts for a significant fraction of the deficit between inclusive measurements and the sum of exclusive semileptonic B decay modes
    Hal - Université Grenoble Alpes
    HAL AMU
    HAL Clermont Université
    Archivio istituzionale della ricerca - Università di Bari
    HAL Université de Savoie
    ePubs: the open archive for STFC research publications
    HAL-IN2P3
    Crossref
    Politecnio die Bari - Catalogo di prodotti della Ricerca
    Archivio della Ricerca - Università degli Studi di Siena
    AIR Universita degli studi di Milano
    Archivio istituzionale della Ricerca - Scuola Normale Superiore
    Archivio della Ricerca - Università di Pisa
    HAL-Polytechnique

    Observation of charmless hadronic b decays

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    Four candidates for charmless hadronic B decay are observed in a data sample of four million hadronic Z decays recorded by the aleph detector at lep. The probability that these events come from background sources is estimated to be less than 10−6. The average branching ratio of weakly decaying B hadrons (a mixture of Bd0, Bs0 and Λb weighted by their production cross sections and lifetimes, here denoted B) into two long-lived charged hadrons (pions, kaons or protons) is measured to be Br(B → h+h−) = (1.7−0.7+1.0 ± 0.2) × 10−5. The relative branching fraction is measured to be 1.0−0.3 −0.1+0.0 +0.0. In addition, branching ratio upper limits are obtained for a variety of exclusive charmless hadronic two-body decays of B hadrons
    Hal - Université Grenoble Alpes
    HAL AMU
    Institutional Knowledge at Singapore Management University
    HAL Clermont Université
    Archivio istituzionale della ricerca - Università di Bari
    HAL Université de Savoie
    CINECA IRIS Institutial research information system UNISS
    ePubs: the open archive for STFC research publications
    Archivio istituzionale della ricerca - Università di Trieste
    HAL-IN2P3
    Crossref
    Politecnio die Bari - Catalogo di prodotti della Ricerca
    Archivio della Ricerca - Università degli Studi di Siena
    AIR Universita degli studi di Milano
    Archivio istituzionale della Ricerca - Scuola Normale Superiore
    Archivio della Ricerca - Università di Pisa
    Copenhagen University Research Information System
    Lancaster E-Prints
    CERN Document Server
    HAL-Polytechnique
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