1,102 research outputs found
Search for the Standard Model Higgs Boson at LEP
No full textThe four LEP collaborations, ALEPH, DELPHI, L3 and OPAL, have collected a total of 2461 pb-1 of e+e- collision data at centre-of-mass energies between 189 and 209 GeV. The data are used to search for the Standard Model Higgs boson. The search results of the four collaborations are combined and examined in a likelihood test for their consistency with two hypotheses: the background hypothesis and the signal plus background hypothesis. The corresponding confidences have been computed as functions of the hypothetical Higgs boson mass. A lower bound of 114.4 GeV/c2 is established, at the 95% confidence level, on the mass of the Standard Model Higgs boson. The LEP data are also used to set upper bounds on the HZZ coupling for various assumptions concerning the decay of the Higgs boson
Study of the KS0KS0 final state in two-photon collisions
No full textThe reaction e+e− →e+e−γ∗γ∗→e+e − K0SK0S is studied with the L3 detector at LEP and the formation of the f2'(1525) resonance is observed. For an integrated luminosity of 114 pb−1, 31±6 f2' events are found. Their angular distribution is consistent with a pure helicity two. The radiative width times the branching ratio is measured to be Γγγ(f'2) × (Br((f'2→ KK̅)keV. Only three events are found in the f2(1270)-a2(1320) mass region, consistent with destructive f2-a2 interference in the KS0KS0 final state. The mixing angle of the tensor meson nonet is determined to the θ = (29.4−1.6+1.4)±
`Study of Neutral Current four fermion and ZZ production in collisions e+ e- at sqrt(s)=183 GeV
No full textA study of neutral-current four-fermion processes is performed using a data sample corresponding to 55.3 pb(-1) of integrated luminosity collected by the L3 detector at LEP at an average centre-of-mass energy of 183 GeV. The neutral-current four-fermion cross sections for final slates with a pair of charged leptons plus jets and with four charged leptons are measured to be consistent with the Standard Model predictions. Events with fermion pair masses close to the Z boson mass are selected in all observable final states and the ZZ production cross section is measured to be sigma ZZ = 0.30(-0.16-0.03)(+0.22 + 0.07) pb, in agreement with the Standard Model expectation. No evidence for the existence of anomalous triple gauge boson ZZZ and ZZ gamma couplings is found and limits on these couplings are set. (C) 1999 Elsevier Science B.V. All rights reserved. RI Fiandrini, Emanuele/C-4549-2008; Achard, Pablo/C-2983-2009; Lista, Luca/C-5719-2008; Kirkby, Jasper/A-4973-2012; Servoli, Leonello/E-6766-201
Generalized event shape and energy flow studies in e+e- annihilation at sqrt(s) = 91.2-208.0 GeV
No full textWe present results from a study of hadronic event structure in high energy e(+)e(-') interactions using the L3 detector at LEP. A new class of event shape distributions are measured at and above the Z boson pole for light quark (u, d, s, c) flavours. Energy flow correlations are studied for all hadronic events. Next-to-leading-log QCD calculations and QCD models with improved leading-log approximations are compared to data and good agreement is found at the Z-pole whereas some discrepancies are observed at higher centre-of-mass energies
Search for Neutral Charmless B Decays at LEP
No full textA search for rare charmlessdecays of Bd0 and Bs0 mesons has been performed in the exclusive channels Bd(s)0 →ηη, Bd(s)0 →ηπ0 and Bd(s)0 →π0π0. The data sample consisted of three million hadronic Z decays collected by the L3 experiment at LEP from 1991 through 1994. No candidate event has been observed and the following upper limits at 90% confidence level on the branching ratios have been set: Br(B()d→ηη) <4.1 x 10−4, Br(B()s→ηη) < 1.5 x 10−3, Br(B()d→ηφ()) < 2.5 x 10−4, Br(B()s→ηphi;()) < 1.0 x 10−3, Br(B()d→phi;()phi;()) < 6.0 x 10−5, Br(B()s→phi;()phi;()) < 2.1 x 10−4.
These are the first experimental limits on Bd0→ηη and on the Bs0neutralcharmless modes
Measurement of the effective weak mixing angle by jet charge asymmetry in hadronic decays of the Z boson
No full textSearch for the standard model Higgs boson in e+ e- interactions at 161-GeV<= s**(1/2) <= 172-GeV
No full textHard-photon production and tests of QED at LEP : L3 Collaboration
No full textThe total and differential cross sections of the process eqeyTMng with nG2 are measured using data collected by the L3 experiment at centre-of-mass energies of 's s183 and 189 GeV. The results are in agreement with the Standard Model expectations. Limits are set on deviations from QED, contact interaction cut-off parameters and masses of excited electrons.Facultad de Ciencias Exacta
Hard-photon production and tests of QED at LEP : L3 Collaboration
No full textThe total and differential cross sections of the process eqeyTMng with nG2 are measured using data collected by the L3 experiment at centre-of-mass energies of 's s183 and 189 GeV. The results are in agreement with the Standard Model expectations. Limits are set on deviations from QED, contact interaction cut-off parameters and masses of excited electrons.Facultad de Ciencias Exacta
Final results of the searches for neutral Higgs bosons in e+ e- collisions at s**(1/2) up to 209-GeV
No full textThe final results of the ALEPH search for the Standard Model Higgs boson at LEP, with data collected in the year 2000 at centre-of-mass energies up to 209 GeV, are presented. The changes with respect to the preceding publication are described and a complete study of systematic effects is reported. The findings of this final analysis confirm the preliminary results published in November 2000 shortly after the closing down of the LEP collider: a significant excess of events is observed, consistent with the production of a 115 \Gcs Standard Model Higgs boson. The final results of the searches for the neutral Higgs bosons of the MSSM are also reported, in terms of limits on \mh, \mA and \tanb. Limits are also set on \mh in the case of invisible decays
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