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    62 research outputs found

    Determination of sin**2 theta(w)(eff) using jet charge measurements in hadronic Z decays

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    The electroweak mixing angle is determined with high precision from measurements of the mean difference between forward and backward hemisphere charges in hadronic decays of the Z. A data sample of 2.5 million hadronic Z decays recorded over the period 1990 to 1994 in the ALEPH detector at LEP is used. The mean charge separation between event hemispheres containing the original quark and antiquark is measured forbb ¯ andcc ¯ events in subsamples selected by their long lifetimes or using fastD*’s. The corresponding average charge separation for light quarks is measured in an inclusive sample from the anticorrelation between charges of opposite hemispheres and agrees with predictions of hadronisation models with a precision of 2%. It is shown that differences between light quark charge separations and the measured average can be determined using hadronisation models, with systematic uncertainties constrained by measurements of inclusive production of kaons, protons andΛ’s. The separations are used to measure the electroweak mixing angle precisely as sin2ϑweff=0.2322±0.0008(exp.stat.) ±0.0007(exp.syst.)±0.0008(sep.). The first two errors are due to purely experimental sources whereas the third stems from uncertainties in the quark charge separations
    Archivio istituzionale della ricerca - Università di Trieste
    Crossref
    Archivio della Ricerca - Università degli Studi di Siena
    AIR Universita degli studi di Milano
    Institutional Knowledge at Singapore Management University
    Archivio della Ricerca - Università di Pisa
    Lancaster E-Prints
    CERN Document Server

    Measurement of the b ---> tau- anti-tau-neutrino X branching ratio and an upper limit on B- ---> tau- anti-tau-neutrino

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    Using 1.45 million hadronic Z decays collected by the ALEPH experiment at LEP, the branching ratio is measured to be 2.75 ± 0.30 ± 0.37%. In addition an upper limit of 1.8 × 10−3 at 90% confidence level is placed upon the exclusive branching ratio of . These measurements are consistent with SM expectations, and put the constraint tan GeV−1 at 90% confidence level on all Type II two Higgs doublet models (such as the MSSM)
    Archivio istituzionale della ricerca - Università di Trieste
    Archivio della Ricerca - Università degli Studi di Siena
    AIR Universita degli studi di Milano
    Archivio della Ricerca - Università di Pisa
    Copenhagen University Research Information System
    ePubs: the open archive for STFC research publications
    Lancaster E-Prints
    CERN Document Server

    Improved tau polarisation measurement

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    Using 22 pb(-1) of data collected at LEP in 1992 on the peak of the Z resonance, the ALEPH collaboration has measured the polarisation of the tau leptons decaying into e nu nu, mu nu nu,pi nu and a(1) nu from their individual decay product distributions. The measurement of the tau polarisation as a function of the production polar angle yields the two parameters A(tau) and A(e), where, in terms of the axial and vector couplings g(Al) and g(nu l), A(l) = 2 g(nu l) g(Al)/(g(nu l)(2) + g(Al)(2)). This analysis follows to a large extent the methods devised for the 1990 and 1991 data but with improvements which bring a better understanding of the systematic uncertainties. Combining the 1992 measurements with our previously published results yields A(tau) = 0.136 +/- 0.012 +/- 0.009 and A(e) = 0.129 +/- 0.016 +/- 0.005. Assuming e-tau universality, the measurements imply an effective weak mixing angle of sin(2) theta(W)(eff) = 0.2332 +/- 0.0014
    AIR Universita degli studi di Milano

    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

    A Measurement of A(b)(FB) in lifetime tagged heavy flavor Z decays

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    A new measurement of the forward-backward asymmetry in Z -> b bbar decays is presented. Hadrons from b decays are tagged using their long lifetimes. The b quark charge and direction are reconstructed with a hemisphere charge algorithm. The asymmetry and reconstructed b hemisphere charge are measured in the 69 pb(-1) of data collected by ALEPH during 1991, 1992 and 1993. They are used to extract sin^2(theta(w)eff), which is determined to be 0.2315 +/- 0.0016 (stat.) +/- 0.0009 (syst.), corresponding to an A(FB)b of 0.00992 +/- 0.0084 (stat.) +/- 0.0046 (stat.)
    Archivio istituzionale della ricerca - Università di Trieste
    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
    Lancaster E-Prints
    CERN Document Server

    Z production cross-sections and lepton pair forward - backward asymmetries

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    Precise values of theZ resonance cross sections and lepton pair forward-backward asymmetries are measured from a sample of 1.3 millionZ decays into hadrons and charged leptons taken with the ALEPH detector at LEP. A silicon-tungsten luminosity calorimeter was installed in ALEPH in 1992, permitting the determination of the absolute luminosity to a systematic precision of 0.15% (experimental) and 0.25% (theoretical). This is combined with a better understanding of the hadronic event selection and an improved tau pair selection. Including the ALEPH results of the past three years one obtains σh0 =(41.60±0.16) nb, andRl=20.69±0.09. The corresponding number of light neutrino species isNv =2.983±0.034. The lepton pair forward-backward asymmetry is used to derive the ratio of vector to axial-vector couplings of leptons:gV2(MZ2)/gA2(MZ2)=0.0058 ±0.0011. An application of these results to constrain one model with extraZ bosons is presented
    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
    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
    Lancaster E-Prints
    CERN Document Server
    HAL-Polytechnique

    Heavy flavor production and decay with prompt leptons in the ALEPH detector

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    Which models and behaviors are underlie the way how research and information retrieval are organized on a scale of international dimension. Each of us is daily confronted to search engine within framework of its activity. These new "libraries" of the Internet rest on logics of classification of the documents very distant from those in our traditional libraries. These new intellectual technologies allow informational discoveries which will change, after a creative process, in knowledge. New practices appear, which use the serendipity like explicit additive of research. The constant interaction between these new practices and these new logical organization of information makes emerge and makes it possible to characterize new contents
    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-Diderot
    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
    Lancaster E-Prints
    CERN Document Server

    K0 production in one prong tau decays

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    From a sample of about 75000 τ decays identified with the ALEPH detector, K0 production in 1-prong hadronic decays is investigated by tagging the KL0 component in a hadronic calorimeter. Results are given for the final states ντh−K0 and ντh−π0K0 where the h− is separated into π and K contributions by means of the dE/dx measurement in in the central detector. The resulting branching ratios are: (Bτ → ντπ−K0) = (0.88±0.14±0.09)%, (Bτ → ντK−K0) = (0.29±0.12±0.03)%, (Bτ → ντπ−π0K0) = (0.33±0.14±0.07)% aand (Bτ → ντK−π0K0) = (0.05±0.05±0.01)%. The K∗ decay rate in the K0π channel agrees with that in the Kπ0 mode: the combined value for the branching ratio is
    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
    Hal-Diderot
    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

    Improved tau polarization measurement

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    Publication venue
    Publication date
    Field of study
    No full text
    Using 22 pb−1 of data collected at LEP in 1992 on the peak of the Z resonance, the ALEPH collaboration has measured the polarisation of the tau leptons decaying intoevv ¯ ,μvv ¯ ,πν, ρν and a1ν from their individual decay product distributions. The measurement of the tau polarisation as a function of the production polar angle yields the two parametersNτ andNe, where, in terms of the axial and vector couplingsgAl andgVl,Nl=2gVl gAl/(gVl2+gAl2). This analysis follows to a large extent the methods devised for the 1990 and 1991 data but with improvements which bring a better understanding of the systematic uncertainties. Combining the 1992 measurements with our previously published results yieldsNτ=0.136±0.012±0.009 andNe=0.129±0.016±0.005. Assuminge−τ universality, the measurements imply an effective weak mixing angle of sin2θWeff=0.2332±0.0014
    HAL-IN2P3
    Crossref
    Archivio della Ricerca - Università degli Studi di Siena
    Hal - Université Grenoble Alpes
    HAL AMU
    Institutional Knowledge at Singapore Management University
    HAL Clermont Université
    Archivio della Ricerca - Università di Pisa
    HAL Université de Savoie
    Lancaster E-Prints
    HAL-Polytechnique

    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
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