806 research outputs found
Search for charged Higgs bosons in e+e- collisions at energies up to sqrt(s) = 209GeV
No full textA search for charged Higgs bosons produced in pairs is performed with data collected at centre-of-mass energies ranging from 189 to 209 GeV by ALEPH at LEP, corresponding to a total luminosity of 629 invpb. The three final states taunutaunu, taunucs and cscs are considered. No evidence for a signal is found and lower limits are set on the mass M_H+ as a function of the branching fraction B(H to taunu). In the framework of a two-Higgs-doublet model, and assuming B(H+ to taunu + B(H+ to cs) = 1 charged Higgs bosons with masses below 79.3 Gev/c2 are excluded at 95% confidence level independently of the branching ratios
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
Measurement of the cross section for open b-quark production in two-photon interactions at LEP RID G-1279-2010
No full textInclusive b-quark production in two-photon collisions has been measured at LEP using an integrated luminosity of 698 pb(-1) collected by the ALEPH detector with root s between 130 and 209 GeV. The b quarks were identified using lifetime information. The cross section is found to be sigma(e(+)e -> e(+)e(-) bb(-)X) = (5.4 +/- 0.8(stat) +/- 0.8(syst)) pb, which is consistent with Next-to-Leading Order QCD
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
A Measurement of the inclusive b → sγ branching ratio
No full textThe flavour changing neutral current decay b → sγ has been detected in hadronic Z decays collected by ALEPH at LEP. The signal is isolated in lifetime-tagged b b ̄ events by the presence of a hard photon associated with a system of high momentum and high rapidity hadrons. The background processes are normalised from the data themselves. The inclusive branching ratio is measured to be (3.11±0.80 stat ±0.72 syst )×10 −4 , consistent with the Standard Model expectation via penguin processes
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