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    174 research outputs found

    Search for the B-c meson

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    In a sample of 3.02 million hadronic Z(0) decays collected by the DELPHI detector, 270 J/psi –> e(+)e(-) candidates have been selected. A search for fully reconstructed B-c(+/-) mesons has yielded one B-c(+/-) –> J/psi pi(+/-) candidate, no B-c(+/-) –> J/psi e(+/-) nu(e) candidates, and one B-c(+/-) –> J/psi pi(+)pi(-)pi(+) candidate, consistent with expected background in each channel. The following 90% confidence level upper limits ate determined: Br(Z(0) –> B-c(+/-) X) x Br(B-c(+/-) –> J/psi pi(+)) < (1.05 to 0.84) x 10(-4) and Br(Z(d) –> B-c(+/-) X) x Br(B-c(+/-) –> J/psi e(+/-) nu(e)) < (5.8 to 5.0) x 10(-5), where the ranges quoted correspond to the range of predicted B-c(+/-) lifetimes from 0.4 to 1.4 ps, and Br(Z(0) –> B-c(+/-) X) x Br(B-c(+/-) –> J/psi pi(+)pi(-)pi(+/-)) < 1.75 x 10(-4), constant over the range of predicted B-c(+/-) lifetimes. (C) 1997 Elsevier Science B.V
    Pergamos : Unified Institutional Repository / Digital Library Platform of the National and Kapodistrian University of Athens

    Measurement of the forward-backward asymmetry of e(+)e(-)-]Z-]B(B)over-bar using prompt leptons and a lifetime tag

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    The forward-backward asymmetry of the process e(+)e(-) --> Z --> b ()overbarbhasbeenmeasuredusingeventscollectedeebytheDELPHIexperimentduringthe1991and1992LEPruns.Thisdatasamplecorrespondedto884000hadronicZdecaysatacentre−of−massenergyrootssimilartoM(Z).Thetaggingofb−quarkeventswasperformedusingtwoapproaches;thefirstwasbasedonthesemileptonicdecaychannelsb−−>X+muandb−−>X+e,thesecondusedalifetimetagwithjet−chargereconstruction.TheresultsofthesetwomethodswerecombinedtogiveA(FB)(b() over bar b has been measured using events collected ee by the DELPHI experiment during the 1991 and 1992 LEP runs. This data sample corresponded to 884 000 hadronic Z decays at a centre-of-mass energy root s similar to M(Z). The tagging of b-quark events was performed using two approaches; the first was based on the semileptonic decay channels b --> X + mu and b --> X + e, the second used a lifetime tag with jet-charge reconstruction. The results of these two methods were combined to give A(FB)(b () over bar b) = 0.107 +/- 0.011(stat. + syst. + mixing). With the semileptonic sample, the forward-backward asymmetry of the process e(+)e(-) --> Z --> c ()overbarcwasalsomeasuredtobeA(FB)(c() over bar c was also measured to be A(FB)(c () over bar c) = 0.083 +/- 0.022(stat.) +/- 0.016(syst.). The effective value of the Weinberg mixing angle derived from these measurements was sin(2) theta(eff)(lep) = 0.2294 +/- 0.0021
    Archivio istituzionale della ricerca - Università dell'Insubria

    MEASUREMENT OF THE GAMMA(B-B-OVER-BAR)/GAMMA(HAD) BRANCHING RATIO OF THE Z BY DOUBLE HEMISPHERE TAGGING

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    Two measurements of Gamma(b ()overbarb)/Gamma(had)arepresented.Bothmeasurementsuse250000ZdecaystakenwiththeDELPHIdetectorin1991andrelymainlyontheprecisionofthemicrovertexdetector.Onetaggingmethodisassimpleaspossiblesothatbackgroundratescanbereliablypredictedbysimulation.Theotheroneusesamoreinvolvedtaggingtechniqueandreducesthedependenceonsimulationasmuchaspossible.Combiningbothresults,Gamma(b() over bar b)/Gamma(had) are presented. Both measurements use 250000 Z decays taken with the DELPHI detector in 1991 and rely mainly on the precision of the microvertex detector. One tagging method is as simple as possible so that background rates can be reliably predicted by simulation. The other one uses a more involved tagging technique and reduces the dependence on simulation as much as possible. Combining both results, Gamma(b () over bar b)/Gamma(had) is found to be 0.2209 +/- 0.0041 (stat.) +/- 0.0042(syst.) +/- 0.0018 (Gamma(c ()overbarc)).TwomeasurementsofGamma(b() over bar c)).Two measurements of Gamma(b () over bar b)/Gamma(had) are presented. Both measurements use 250000 Z decays taken with the DELPHI detector in 1991 and rely mainly on the precision of the microvertex detector. One tagging method is as simple as possible so that background rates can be reliably predicted by simulation. The other one uses a more involved tagging technique and reduces the dependence on simulation as much as possible. Combining both results, Gamma(b ()overbarb)/Gamma(had)isfoundtobe0.2209+/−0.0041(stat.)+/−0.0042(syst.)+/−0.0018(Gamma(c() over bar b)/Gamma(had) is found to be 0.2209 +/- 0.0041 (stat.) +/- 0.0042(syst.) +/- 0.0018 (Gamma(c () over bar c))
    Archivio istituzionale della ricerca - Università degli Studi di Udine
    Archivio istituzionale della ricerca - Università dell'Insubria

    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 <b(b)over bar> 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(<b(b)over bar>)/Gamma(had) = 0.2216 +/- 0.0016(stat.) +/- 0.0021(syst.) was found, where the <c(c)over bar> production fraction was fixed to its Standard Model value
    Archivio istituzionale della ricerca - Università degli Studi di Udine
    Archivio istituzionale della ricerca - Università dell'Insubria

    Measurement of the partial decay width Rb0_{b}^{0} = Γbb‾\Gamma_{b\overline{b}}/Γhad\Gamma_{had} of the Z with the DELPHI detector at LEP

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    The partial decay width of the Z to b\overline{ b} 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: ΓbbˉΓhad=0.2216±0.0016(stat.)±0.0021(syst.) \frac{\Gamma_{b \bar{b}}}{\Gamma_{had}} = 0.2216 \pm 0.0016(stat.) \pm 0.0021 (syst.) was found, where the c\overline{c} production fraction was fixed to its Standard Model value
    Hal - Université Grenoble Alpes
    HAL AMU
    Archivio istituzionale della ricerca - Università di Genova
    Hal-Diderot
    Archivio istituzionale della ricerca - Università di Padova
    HAL-IN2P3
    Portail HAL du Collège de France
    Oxford University Research Archive
    DSpace@NTUA (National Technical Univ. of Athens)
    CERN Document Server
    HAL
    HAL Portal UDL Université de Lyon

    B-asterisk production in Z-Decays

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    The decay B* --> B gamma has been observed with the DELPHI detector at LEP, where the B* meson is produced in Z boson decays, The combination of inclusively reconstructed B mesons with well-measured converted photons yields a measurement of the flavour-averaged B* - B mass difference of 45.5 +/- 0.3 (stat.) +/- 0.8 (syst.) MeV/c(2). 95% confidence level upper limits at 6 MeV/c(2) are placed on both the isospin (i.e, B+-B-0) and the B-s-B-ud splitting of the mass difference, The production ratio of B* to B mesons in Z decays is measured to be 0.72 +/- 0.03 (stat.) +/- 0.06 (syst.). Limits on the production cross-section of other hypothetical excited B hadron states decaying radiatively are established. The differential B* cross section has been measured to be in good agreement with the average b fragmentation, yielding an average fractional B* energy of [x(E)] = 0.695 +/- 0.009 (stat.) +/- 0.013 (syst.). From the decay angular distribution the relative contribution of longitudinal B* polarisation states is measured to be sigma(L)/(sigma(L) + sigma(T)) = 0.32 +/- 0.04 (stat.) +/- 0.03 (syst.)
    Archivio istituzionale della ricerca - Università degli Studi di Udine
    Hal - Université Grenoble Alpes
    HAL AMU
    Archivio istituzionale della ricerca - Università dell'Insubria
    Repositori d'Objectes Digitals per a l'Ensenyament la Recerca i la Cultura
    DI-fusion
    ePubs: the open archive for STFC research publications
    Archivio istituzionale della ricerca - Università di Genova
    Hal-Diderot
    Archivio istituzionale della ricerca - Università di Padova
    Archivio istituzionale della ricerca - Università di Trieste
    HAL-IN2P3
    Crossref
    Portail HAL du Collège de France
    Oxford University Research Archive
    DSpace@NTUA (National Technical Univ. of Athens)
    CERN Document Server
    HAL
    HAL Portal UDL Université de Lyon

    Lifetime and production rate of beauty baryons from Z decays

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    The production and decay of beauty baryons (b-baryons) have been studied using 1.7 x 10(6) Z hadronic decays collected by the DELPHI detector at LEP. Three different techniques were used to identify the b-baryons. The first method used pairs of a Lambda and a lepton to tag the b-baryon decay. The second method associated fully reconstructed Lambda(c) baryons with leptons. The third analysis reconstructed the b-baryon decay points by forming secondary vertices from identified protons and muons of opposite sign. Using these methods the following production rates were measured: f(b --> b-baryon) x BR(b-baryon --> Lambda l nu(l)X) = (0.30 +/- 0.06 +/- 0.04)%, f(b --> b-baryon) x BR(b-baryon --> Lambda(c)l nu(l)X) = (1.18 +/- 0.26(-0.21)(+0.31)%, f(b --> b-baryon) x BR(b-baryon --> p mu nu(mu)X) = (0.49 +/- 0.11 +/- (+0.15)(-0.11)%. The average b-baryon lifetime was determined to be: tau = 1.21(-0.18)(+.21)(stat.) +/- 0.04(exp.syst.)(-.07)(+.02)(th.syst,) ps
    Archivio istituzionale della ricerca - Università degli Studi di Udine
    Archivio istituzionale della ricerca - Università dell'Insubria
    ePubs: the open archive for STFC research publications

    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
    Archivio istituzionale della ricerca - Università degli Studi di Udine
    Hal - Université Grenoble Alpes
    HAL AMU
    Archivio istituzionale della ricerca - Università dell'Insubria
    Repositori d'Objectes Digitals per a l'Ensenyament la Recerca i la Cultura
    DI-fusion
    ePubs: the open archive for STFC research publications
    Archivio istituzionale della ricerca - Università di Genova
    Hal-Diderot
    Archivio istituzionale della ricerca - Università di Padova
    Portail HAL-PSL
    Archivio istituzionale della ricerca - Università di Trieste
    Archivio della ricerca - Università degli studi di Napoli Federico II
    HAL-IN2P3
    Crossref
    Portail HAL du Collège de France
    Portail HAL de l’Université Claude Bernard Lyon
    Oxford University Research Archive
    DSpace@NTUA (National Technical Univ. of Athens)
    DIAL UCLouvain
    CERN Document Server
    HAL
    HAL Portal UDL Université de Lyon

    Search for pair production of heavy objects in 4 jet events at s**(1/2) = 130-GeV - 136-GeV

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    Results are presented of a search for pair production of heavy objects decaying into four hadronic jets, as expected for example from associated or pair production of MSSM Higgs bosons, \hA ~or \HH, using a data sample of 5.9  5.9\;pb−1^{-1} of e+e−e^+ e^- collisions at s=130−136  GeV\sqrt{s}=130-136\;{\mathrm {GeV}} collected with the DELPHI detector at LEP in November 1995. The data and expectations from standard processes agree after four-jet selections. An analysis based on bb-tagging finds no \hA ~candidate with high mass. A study optimized to search for \HH ~events with mass in the 40−50  GeV/c240-50 \; {\mathrm{GeV}}/c^2 range also finds no candidate. Finally a comparison is made with a recent ALEPH analysis which found an excess of four-jet events with high multiplicity and high mass. Such a signal is not observed in the DELPHI data, although a slight excess in the mass region around 105  GeV/c2105 \; {\mathrm{GeV}}/c^2 is seen
    Archivio istituzionale della ricerca - Università degli Studi di Udine
    Hal - Université Grenoble Alpes
    HAL AMU
    Repositori d'Objectes Digitals per a l'Ensenyament la Recerca i la Cultura
    ePubs: the open archive for STFC research publications
    The University of Manchester - Institutional Repository
    Archivio istituzionale della ricerca - Università di Genova
    Hal-Diderot
    UvA-DARE
    International Migration, Integration and Social Cohesion online publications
    Archivio istituzionale della ricerca - Università di Padova
    Archivio istituzionale della ricerca - Università di Trieste
    Archivio della ricerca - Università degli studi di Napoli Federico II
    HAL-IN2P3
    Crossref
    Portail HAL du Collège de France
    DSpace@NTUA (National Technical Univ. of Athens)
    DIAL UCLouvain
    CERN Document Server
    HAL
    HAL Portal UDL Université de Lyon

    A Measurement of the photon structure function F2(gamma) at an average Q**2 of 12-GeV**2/c**4

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    The hadronic photon structure function F2γ has been measured in the Q2 range from 4 to 30 GeV2/c4 and down to x values of order 0.001, using data taken with the DELPHI detector at LEP between 1991 and 1993. A comparison is made with several F2γ parameterizations with special emphasis on their low x behaviour. A result on the Q2 evolution of F2γ is presented. © Springer-Verlag 1996
    Archivio istituzionale della ricerca - Università degli Studi di Udine
    Hal - Université Grenoble Alpes
    HAL AMU
    Archivio istituzionale della ricerca - Università dell'Insubria
    ePubs: the open archive for STFC research publications
    The University of Manchester - Institutional Repository
    Archivio istituzionale della ricerca - Università di Genova
    Hal-Diderot
    UvA-DARE
    International Migration, Integration and Social Cohesion online publications
    Archivio istituzionale della ricerca - Università di Padova
    Archivio della ricerca - Università degli studi di Napoli Federico II
    HAL-IN2P3
    Crossref
    Portail HAL du Collège de France
    Oxford University Research Archive
    DSpace@NTUA (National Technical Univ. of Athens)
    DIAL UCLouvain
    HAL
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