173 research outputs found

    Study of prompt photon production in hadronic Z0 decays

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    From a sample of 1.5 million \zqq decays collected by the DELPHI detector during 1991, 1992 and 1993, the production cross section for isolated final state photons is measured and is compared with the {\order} (\ae , \as ) matrix element calculations implemented in the EEPRAD and GNJETS Monte Carlo generators. The observed photon yield is used to derive the electroweak couplings of charge 2/3 (u-type) and charge 1/3 (d-ska, Agni

    PRODUCTION OF CHARGED-PARTICLES, K-S(0),K+/-, P AND LAMBDA IN Z-]B(B)OVER-BAR EVENTS AND IN THE DECAY OF B-HADRONS

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    A sample of events enriched in <b(b)over bar> quark pairs was selected in the data recorded by the DELPHI experiment at LEP during 1992 and 1993, by the presence of secondary decay vertices from short-lived particles. Using this sample, the average multiplicities of K-S(0), K-+/-, p((p) over bar), Lambda(<(Lambda)over bar>) and of charged particles in <b(b)over bar> events have been measured, distinguishing the component from fragmentation and the component coming from the decay of b-hadrons. The measurement of the average charge multiplicity in <b(b)over bar> events was used to compute the mean fractional beam energy carried by the primary b-hadron, and the difference in charged particle multiplicity between <b(b)over bar> events and light quark (<u(u)over bar>, <d(d)over bar>, <s(s)over bar>) events

    Study of prompt photon production in hadronic Z0 decays

    No full text
    From a sample of 1.5 million Z0→qq decays collected by the DELPHI detector during 1991, 1992 and 1993, the production cross section for isolated final state photons is measured and is compared with the O(α, αs) matrix element calculations implemented in the EEPRAD and GNJETS Monte Carlo generators. The observed photon yield is used to derive the electroweak couplings of charge 2/3 (u-type) and charge 1/3 (d-type) quarks to the Z0 boson. The measured values c2/3=0.91-0.36+0.25 and c1/3=1.62-0.17+0.24 are compatible with the Standard Model prediction, c2/3=1.145 and c1/3=1.477. © 1996 Springer-Verlag

    Multiplicity fluctuations in hadronic final states from the decay of the Z0

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    An analysis of the fluctuations in the phase space distribution of hadrons produced in the decay of 78829 Z0 has been carried out, using the method of factorial moments. The high statistics collected by the DELPHI experiment at LEP during 1990 allowed studies of the event sample both globally and in intervals of ρt and multiplicity, and for different jet topologies and for single jets. A large contribution to the factorial moments of the one-dimensional data on rapidity with respect to the event axis comes from hard gluons. Details of factorial moments in two and three dimensions are presented. Influences of resonance decays have been studied by Monte Carlo simulation: one-dimensional factorial moments at low pt, and two-, three-dimensional analyses are affected. Parton shower models describe the data reasonably well.0SCOPUS: ar.jinfo:eu-repo/semantics/publishe

    STUDY OF PROMPT PHOTON PRODUCTION IN HADRONIC Z(0) DECAYS

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    From a sample of 1.5 million Z(0) –> <q(q)over bar> decays collected by the DELPHI detector during 1991, 1992 and 1993, the production cross section for isolated final state photons is measured and is compared with the O(alpha, alpha(s)) matrix element calculations implemented in the EEPRAD and GNJETS Monte Carlo generators. The observed photon yield is used to derive the electroweak couplings of charge 2/3 (u-type) and charge 1/3 (d-type) quarks to the Z(0) boson. The measured values C-2/3 = 0.91(-0.36)(+0.25) and c(1/3) = 1.62(-0.17)(+0.24) are compatible with the Standard Model prediction, C-2/3 = 1.145 and c(1/3) = 1.477

    A Study of B0 - anti-B0 mixing using semileptonic decays of B hadrons produced from Z0

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    The B0-B̄0 mixing was studied by using about 250000 hadronic decays of the Z0,_collected with the DELPHI detector at LEP. With 1665 dilepton events, the probability for a b quark to become a b̄ before decaying was found to be χ = 0.121-0.040 0.044 ± 0.017. The semileptonic branching ratio of the b was measured from the dilepton and single lepton events and found to be Br(b → l) = (10.0 ± 0.7 ± 0.7)%.0SCOPUS: ar.jinfo:eu-repo/semantics/publishe

    A MEASUREMENT OF B-MESON PRODUCTION AND LIFETIME USING DL- EVENTS IN Z(0) DECAYS

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    A study of B meson decays into D l- X final states is presented. In these events, neutral and charged D mesons originate predominantly from B+ and B0 decays, respectively. The dilution of this correlation due to D** production has been taken into account. From 263700 hadronic Z0 decays collected in 1991 with the DELPHI detector at the LEP collider, 92 D0 --> K- pi+, 35 D+ --> K- pi+ pi+ and 61 D*+ --> D0 pi+ followed by D0 --> K- pi+ or D0 --> K- pi+ pi+ pi-, are found with an associated lepton of the same charge as the kaon. From the D0 l- and D*+ l-, the probability f(d) that a b quark hadronizes into a B- (or B0BAR),meson is found to be 0.44 +/-0.08 +/-0.09, corresponding to a total (B(s) + LAMBDA(b)) hadronization fraction of 0.12(-0.12)+0.24 .By reconstructing the energy of each B meson, the b quark fragmentation is directly measured for the first time. The mean value of the B meson energy fraction is: [X(E)(B)] = 0.695+/-0.015(stat.)+/-0.029(syst.) Reconstructing D-lepton vertices, the following B life-times are measured: tau(B) = 1.27(-0.18)+0.22(stat.)+/-0.15(syst.) ps, where bBAR --> D0 l- X, tau(B) = 1.18(-0.27)+0.39(stat.)+/-0.15(syst.) ps, where BBAR --> D+ l- X, T(B) = 1.19(-0.19)+0.25(stat.)+/-0.15(syst.) ps where BBAR --> D*+ l- X, and an average tau(B) = 1.23(-0.13)+0.14(stat.)+/-0.15(syst.) ps is found. Allowing for decays into D** l- vBAR, the B+ and B0 lifetimes are: tau(B+)= 1.30(0.29)+0.33(stat.)+/-0.15(syst. exp.) +/-0.05(syst. D**) ps, tau(B0)= 1.17(-0.23)+0.29(stat.)+/-0.15(syst. exp.) +/-0.05 (syst. D**) ps, tau(B+)/tau(B0) = 1.11(0.39)+0.51(stat.)+/-0.05(syst. exp.) +/-0.10(syst. D**) ps

    A Measurement of the tau lifetime

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    The tau lepton lifetime is measured using four different methods with the DELPHI detector. Three measurements using one prong decays are combined, accounting for correlations, resulting in ττ=298 ±7 (stat.)±4 (syst.) fs while the decay length distribution of three prong decays gives ππ=298±13 (stat)±(syst.) fs. The combined result is ττ=298±7 fs. The ratio of the Fermi coupling constant from tau decay relative to that from muon decay is found to be 0.985±0.013, compatible with lepton universality
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