Single top production in e+e− annihilations is searched for in data collected by the L3 detector at centre-of-mass energies from 189 to 209 GeV, corresponding to a total integrated luminosity of ...634 pb−1. Investigating hadronic and semileptonic top decays, no evidence of single top production at LEP is obtained and upper limits on the single top cross section as a function of the centre-of-mass energy are derived. Limits on possible anomalous couplings, as well as on the scale of contact interactions responsible for single top production are determined.
We search, in the context of extra-dimension scenarios, for the possible existence of brane fluctuations, called branons. Events with a single photon or a single Z-boson and missing energy and ...momentum collected with the L3 detector in e+e− collisions at centre-of-mass energies 2=189–209 GeV are analysed. No excess over the Standard Model expectations is found and a lower limit at 95% confidence level of 103 GeV is derived for the mass of branons, for a scenario with small brane tensions. Alternatively, under the assumption of a light branon, brane tensions below 180 GeV are excluded.
The CP-conserving triple-gauge-boson couplings, g1Z, κγ, λγ, g5Z, κZ and λZ are measured using hadronic and semi-leptonic W-pair events selected in 629 pb−1 of data collected at LEP with the L3 ...detector at centre-of-mass energies between 189 and 209 GeV. The results are combined with previous L3 measurements based on data collected at lower centre-of-mass energies and with the results from single-W production and from events with a single-photon and missing energy. Imposing the constraints κZ=g1Z−tan2θW(κγ−1) and λZ=λγ, we obtain for the C and P conserving couplings the results: g1Z=0.966±0.033(stat)±0.015(syst),κγ=1.013±0.066(stat)±0.026(syst),λγ=−0.021±0.035(stat)±0.017(syst). Results from the analysis of fully leptonic W-pair decays are also given. All results are in agreement with the Standard Model expectations and confirm the existence of self-couplings among electroweak gauge bosons.
The amplitude of the signal collected from the PbWO4 crystals of the CMS electromagnetic calorimeter is reconstructed by a digital filtering technique. The amplitude reconstruction has been studied ...with test beam data recorded from a fully equipped barrel supermodule. Issues specific to data taken in the test beam are investigated, and the implementation of the method for CMS data taking is discussed.
The cross section of W-boson pair-production is measured with the L3 detector at LEP. In a data sample corresponding to a total luminosity of 629.4 pb−1, collected at centre-of-mass energies ranging ...from 189 to 209 GeV, 9834 four-fermion events with W bosons decaying into hadrons or leptons are selected. The total cross section is measured with a precision of 1.4% and agrees with the Standard Model expectation. Assuming charged-lepton universality, the branching fraction for hadronic W-boson decays is measured to be: Br(W→hadrons)=67.50±0.42(stat.)±0.30(syst.)%, in agreement with the Standard Model. Differential cross sections as a function of the W− production angle are also measured for the semi-leptonic channels qqeν and qqμν.
Search for charged Higgs bosons at LEP Aloisio, A.; Alviggi, M.G.; Arefiev, A. ...
Physics letters. B,
11/2003, Letnik:
575, Številka:
3-4
Journal Article
Recenzirano
Odprti dostop
A search for pair-produced charged Higgs bosons is performed with the L3 detector at LEP using data collected at centre-of-mass energies between 189 and 209 GeV, corresponding to an integrated ...luminosity of 629.4 pb−1. Decays into a charm and a strange quark or into a tau lepton and its neutrino are considered. No significant excess is observed and lower limits on the mass of the charged Higgs boson are derived at the 95% confidence level. They vary from 76.5 to 82.7 GeV, as a function of the H±→τν branching ratio.
The shadowing of high-energy cosmic rays by the Moon has been observed with a significance of 9.4 standard deviations with the L3
+
C muon spectrometer at CERN. A significant effect of the Earth ...magnetic field is observed. Since no event deficit on the east side of the Moon has been observed, an upper limit at 90% confidence level on the antiproton to proton ratio of 0.11 is obtained for primary energies around 1
TeV.
The formation of the
η′ in the reaction e
+e
−→e
+e
−
η′→e
+e
−
π
+
π
−
γ has been measured by the L3 detector at a centre-of-mass energy of 91
GeV
. The radiative width of the
η′ has been found to ...be
Γ
γγ=4.17±0.10
(stat.)±0.27
(sys.)
keV
. The
Q
2 dependence of the
η′ formation cross section has been measured for
Q
2≤10
GeV
2
and the
η′ electromagnetic transition form factor has been determined. The form factor can be parametrised by a pole form with
Λ=0.900±0.046
(stat.)±0.022
(sys.)
GeV
. It is also consistent with recent non-perturbative QCD calculations.
We report on a search for the first generation heavy neutrino that is an isosinglet under the standard SU(2)L gauge group. The data collected with the L3 detector at center-of-mass energies between ...130 GeV and 208 GeV are used. The decay channel Ne→eW is investigated and no evidence is found for a heavy neutrino, Ne, in a mass range between 80 GeV and 205 GeV. Upper limits on the mixing parameter between the heavy and light neutrino are derived.
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