1,721,230 research outputs found
Search For the Decays B-d(0)-]gamma-gamma and B-s(0)-]gamma-gamma
No full textA search for the decays B-d,s(0) --> gamma gamma in 2.95 million hadronic Z decays has been performed using the L3 detector at LEP. No candidates are found in the signal region and upper limits have been set on the branching ratios: Br(B-d(0) --> gamma gamma) gamma gamma) < 14.8 x 10(-5) at 90% CL. These are the first limits set on these exclusive rare decays
Tests Qed At Lep Energies Using E(+)e(-)-]gamma-gamma(gamma) and E(+)e(-)-]l(+)l(-)gamma-gamma
No full textTotal and differential cross sections for the process e(+)e(-) --> gamma gamma(gamma), and the total cross section for the process e(+)e(-) --> gamma gamma gamma, are measured at energies around 91 GeV using the data collected with the L3 detector from 1991 to 1993. We set lower limits, at 95% CL, on a contact interaction energy scale parameter Lambda > 602 GeV, on the mass of an excited electron m(c)* > 146 GeV and on the QED cut-off parameters Lambda(+) > 149 GeV and Lambda(-) > 143 GeV. Upper limits are also set on the branching fractions of Z decaying into gamma gamma, pi degrees gamma and eta gamma of 5.2 x 10(-5), 5.2 x 10(-5) and 7.6 x 10(-5) respectively. The reactions e(+)e(-) --> rho(+)rho(-)n gamma (rho = e, mu, tau) are studied using the data collected from 1990 to 1994. The data are consistent with the QED expectations
Search For Anomalous Z-]gamma-gamma-gamma Events At Lep
No full textWe have searched for anomalous Z --> gamma gamma gamma events with the L3 detector at LEP. No significant deviations from the expected QED e(+)e(-)-->gamma gamma gamma events are observed. The branching ratio upper limit for a composite Z decaying directly into three photons is found to be 1.0 x 10(-1) at 95% C.L. The branching ratio upper limits for the process Z-->gamma X,X-->gamma gamma are in the range of 0.4 to 1.3 x 10(-5), depending on the mass and width of the scalar particle X. In the context of a model with magnetic monopoles coupling to the Z, we find BR(Z-->gamma gamma gamma) < 0.8 x 10(-5) at 95% C.L; this results in a lower mass limit of 510 GeV for a magnetic monopole
Measurement of the Lifetime of B-hadrons and A Determination of [vcb]
No full textFrom a fit to the impact parameter distribution of lepton tracks from semileptonic b decay, the lifetime of B-hadrons produced in e+e- collisions at the Z0 is measured to be 1.32 +/- 0.08 (stat.) +/- 0.09 (syst.) ps. Combined with an earlier measurement of the branching ratio Br(B --> lvX), the CKM matrix element \V(cb)\ is determined to be 0.046 +/- 0.002 (exp.) -0.003(+0.004) (theory)
Measurement of Eta(c) Production In Untagged 2-photon Collisions At Lep
No full textA study of twelve distinct decay channels of the eta(c) has been performed with the L3 detector at LEP, for an integrated luminosity of 30 pb-1. Summing all channels, 28 candidate events have been identified, with an estimated background of 11 events. The two-photon radiative width is evaluated to be GAMMA(gammagamma) (eta(c)) = 8.0 +/- 2.3 +/- 2.4 keV
Measurement of the Weak Charged Current Structure In Semileptonic B-hadron Decays At the Z-peak
No full textThe neutrino energy spectrum in semileptonic b-hadron decays with identified energetic electrons and muons has been measured. The observed relative energy sharing between the neutrino and the charged lepton is found to be well described with a W-+/- polarization obtained from a free b-quark decay model with a (V-A)x(V-A) decay structure. The alternative of a (V+A) x(V-A) decay structure is excluded with a significance of more than 6 standard deviations. The possibility that hadronic corrections to the b-hadron decay destroy any W-+/- polarization is disfavored by more than 3 standard deviations
Energy and Particle Flow In 3-jet and Radiative 2-jet Events From Hadronic Z-decays
No full textWe report on a detailed study of the energy and particle flow in the event plane of three-jet events q(q) over barg events as compared with events. Several QCD model predictions are compared with the observed effect
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Performance On Test Beam of the L3 Double-sided Silicon Microstrip Detector
No full textTwo modules of the L3 Silicon Microvertex Detector (SMD) have been tested on beam. The active area of the modules consists of double sided silicon microstrip detectors; the implantation pitch is 25 mum and 50 mum in the junction and ohmic side, respectively. The detectors are read out by a VLSI radiation hard amplifier (SVX-H). The position resolution, with a readout pitch of 50 mum and 200 mum for the two sides, is determined to be 7.0 mum and 14.3 mum. A signal to noise ratio greater-than-or-equal-to 16 and a detection efficiency greater-than-or-equal-to 99% are measured for both sides
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