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    464 research outputs found

    Underground neutrino detectors

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    CERN Document Server

    Charmed particle lifetimes from experiment WA58

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    CERN Document Server

    Search For Radiative B-meson Decays

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    The Crystal Ball detector at the e+ e- storage ring DORIS-II has been used to search for radiative B meson decays, especially of the type b --> s-gamma. No monoenergetic gamma-lines have been found in the inclusive photon spectrum from UPSILON(4S) decays, and upper limits are obtained for radiative decays of B mesons to various strange mesons and to the D*. Integrating the photon spectrum over the corresponding energy range, we find BR (B--> gamma-X) < 2.8 x 10(-3), at 90% confidence level for the mass range 892 MeV less-than-or-equal-to M(X) less-than-or-equal-to 2045 MeV
    Archivio istituzionale della ricerca - Università di Modena e Reggio Emilia

    The Electron Spectrum From B-meson Decays

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    The Crystal Ball Collaboration has measured the energy spectrum of electrons from semileptonic B meson decays at the e+ e– storage ring DORIS II. Branching ratios and weak mixing angles of the Kobayashi-Maskawa matrix are determined using several models for the hadronic matrix elements. We obtain the branching ratio for semileptonic B decays to charmed states BR(B -> e nu Xc )=(11.7+-0.4+-1.0)%. Our result for the corresponding Kobayashi-Maskawa matrix element is |Vcb |=0.052+-0.006. The model dependence of both results is included in the error. We have not observed semileptonic B decays to non-charmed mesons. Analyzing the measured electron spectrum above 2.4 GeV, where no b->c decays contribute, we find BR(B -> e nu Xu )/BR(B -> e nu Xc )<6.5% at the 90% confidence level.this corresponds to an upper limit |V ub /V cb |
    DESY Publication Database
    DESY
    Archivio istituzionale della ricerca - Università di Modena e Reggio Emilia

    Measurement of the average lifetime of b-hadrons in Z decays RID C-4549-2008 RID C-5719-2008

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    We present a measurement of the average b-hadron lifetime tau(b) at the e(+)e(-) collider LEP. Using hadronic Z decays collected in the period from 1991 to 1994, two independent analyses have been performed. In the first one, the b-decay position is reconstructed as a secondary vertex of hadronic b-decay particles. The second analysis is an updated measurement of tau(b) using the impact parameter of leptons with high momentum and high transverse momentum. The combined result is tau(b) = [1549 +/- 9 (stat) +/- 15 (syst)] fs. In addition, we measure the average charged b-decay multiplicity [n(b)] and the normalized average b-energy [x(E)](b) at LEP to be [n(b)] = 4.90 +/- 0.04 (stat) +/- 0.11 (syst), [x(E)](b) = 0.709 +/- 0.004 (stat + syst). (C) 1998 Published by Elsevier Science B.V
    Archivio della Ricerca - Università di Roma 3
    Archivio della ricerca- Università di Roma La Sapienza

    Measurements of the bb‾b\overline{b} production cross section and forward- backward asymmetry at centre-of-mass energies above the Z pole at LEP

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    The measurements of R_{b} = \sigma(e^+e^-} \to b\overline{b})/\sigma( e^+e^-} \to{m q\overline{q}) and of the b quarkforward--backward charge asymmetry,A_fb}^{b}, at centre--of--mass energies above the Z pole are described. The measurement of RbR_{b} is performed at s\sqrt{s} between 130 and 189 GeV using a b--tagging method thatexploits the relatively large decay length ofb--hadrons. The measurement of AfbbA_{fb}^{b} is performedusing the large statistics event sample collected at s\sqrt{s}=189 GeV with a lepton--tag analysis based on the selection of prompt muons and electrons. The results at s\sqrt{s}=189 GeV are: Rb=0.163pm0.013(stat.)pm0.005(syst.)R_{b} = 0.163 pm 0.013 (stat.) pm 0.005 (syst.), Afbb=0.61pm0.18(stat.)pm0.09(syst.).A_{fb}^{b} = 0.61 pm 0.18 (stat.) pm 0.09 (syst.).The measurements of R b =σ( e + e − → b b ̄ )/σ( e + e − → q q ̄ ) and of the b quark forward–backward charge asymmetry, A fb b , at centre-of-mass energies above the Z pole are described. The measurement of R b is performed at s between 130 and 189 GeV using a b-tagging method that exploits the relatively large decay length of b-hadrons. The measurement of A fb b is performed using the large statistics event sample collected at s =189 GeV with a lepton-tag analysis based on the selection of prompt muons and electrons. The results at s =189 GeV are R b =0.163±0.013 (stat.) ±0.005 (syst.) , A fb b =0.61±0.18 (stat.) ±0.09 (syst.) .The measurements of Rb = sigma(e+e- -> bb~)/sigma(e+e- -> qq~) and of the b quark forward-backward charge asymmetry, A^b_fb, at centre-of-mass energies above the Z pole are described. The measurement of Rb is performed at \root{s} between 130 and 189 GeV using a b-tagging method that exploits the relatively large decay length of b-hadrons. The measurement of A^b_fb is performed using the large statistics event sample collected at \root{s}=189 GeV with a lepton-tag analysis based on the selection of prompt muons and electrons. The results at \root{s}=189 GeV are: Rb = 0.163 +/- 0.013 (stat.) +/- 0.005 (syst.), A^b_fb = 0.61 +/- 0.18 (stat.) +/- 0.09 (syst.)
    Hal - Université Grenoble Alpes
    DESY
    Publikationsserver der RWTH Aachen University
    HAL Université de Savoie
    DESY Publication Database
    Archivio della ricerca - Università degli studi di Napoli Federico II
    HAL-IN2P3
    Portail HAL de l’Université Claude Bernard Lyon
    Oxford University Research Archive
    CERN Document Server
    Archivio della ricerca- Università di Roma La Sapienza
    HAL

    Measurement of the average lifetime of b-hadrons in Z decays

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    We present a measurement of the average b-hadron lifetime τb{\rm \tau_b} at the e+e− \mathrm{e^+e^-} \, collider LEP. Using hadronic Z decays collected in the period from 1991 to 1994, two independent analyses have been performed. In the first one, the b-decay position is reconstructed as a secondary vertex of hadronic b-decay particles. The second analysis is an updated measurement of τb{\rm \tau_b} using the impact parameter of leptons with high momentum and high transverse momentum. The combined result is \begin{center} τb=[1549±9 (stat) ±15 (syst)]  fs {\rm \tau_b= [ 1549 \pm 9 \, (stat) \, \pm 15 \, (syst) ] \; fs \,} . \end{center} In addition, we measure the average charged b-decay multiplicity ⟨nb⟩{\rm \langle n_{\rm b}} \rangle and the normalized average b-energy ⟨xE⟩b{\rm \langle x_E \rangle_{\rm b}} at LEP to be \begin{center} ⟨nb⟩=4.90±0.04 (stat)±0.11 (syst){\rm \langle n_{\rm b} \rangle = 4.90 \pm 0.04 \ (stat) \pm 0.11 \, (syst)} , \end{center} \begin{center} ⟨xE⟩b=0.709±0.004 (stat+syst).{\rm \langle x_E \rangle_{\rm b} = 0.709 \pm 0.004 \, (stat + syst).} \end{center
    DESY Publication Database
    Archivio della ricerca - Università degli studi di Napoli Federico II
    HAL-IN2P3
    Crossref
    Hal - Université Grenoble Alpes
    DESY
    Publikationsserver der RWTH Aachen University
    HAL Université de Savoie
    CERN Document Server
    HAL

    Upper limit on the lifetime difference of short- and long-lived Bs0B^0_s mesons

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    An upper limit on the lifetime difference of short- and long-lived Bs0\rm B^0_s mesons has been obtained using an inclusive bottom hadron sample from 2 million hadronic Z decays collected by the L3 experiment at LEP. A lifetime fit has been performed on data samples separately enriched in neutral and charged b hadrons. An experimental upper limit on the decay rate difference of short- and long-lived Bs0\rm B^0_s mesons of \begin{displaymath} ~~~~ {\rm (|\Delta\Gamma|/\Gamma)_{B^0_s}} < 0.67 ~~~~~~~\mathrm{(95\% \; C.L.)} \end{displaymath} has been determined. In addition, the lifetimes of B+\rm B^+ and Bd0\rm B^0_d mesons have been measured to be τ(B+)=1.66±0.06 ±0.03  ps\tau(\rm B^+) = 1.66 \pm 0.06 \, \pm 0.03 \; \mathrm{ps} and τ(Bd0)=1.52±0.06 ±0.04  ps\tau(\rm B^0_d) = 1.52 \pm 0.06 \, \pm 0.04 \; \mathrm{ps}, where the first errors are statistical and the second are systematic
    Hal - Université Grenoble Alpes
    DESY
    Publikationsserver der RWTH Aachen University
    HAL Université de Savoie
    DESY Publication Database
    Archivio della ricerca - Università degli studi di Napoli Federico II
    HAL-IN2P3
    Crossref
    Archivio della Ricerca - Università di Roma 3
    Oxford University Research Archive
    CERN Document Server
    Archivio della ricerca- Università di Roma La Sapienza
    HAL
    HAL Portal UDL Université de Lyon

    Search For Exotic Tau-decays

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    The Crystal Ball detector at the Doris II storage ring at DESY was used to search for the exotic decay processes tau -&gt; e gamma, tau -&gt; e pi0, tau -&gt; e eta. No signal was observed. We obtained the following 90% CL upper limits on the branching fractions:B(tau -&gt; e gamma)&lt; 2.0x10^(-4),B(tau -&gt; e pi0) &lt; 1.4x10^(-4),B(tau -&gt; e eta) &lt; 2.4x10^(-4)
    DESY Publication Database
    DESY
    Archivio istituzionale della ricerca - Università di Modena e Reggio Emilia

    Measurements of Z0^{0} --> bb‾\overline{b} decays and the semileptonic branching ratio Br(b --> l + X)

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    CERN Document Server
    IRIS - Res&Arch Institutional Research Information System Università degli Studi di Perugia
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