0000000000667603
AUTHOR
M. Fernandez Bosman
Search for contact interactions in the reactionse + e −→l + l − ande + e −→γγ
Contact interactions are searched for using the differential cross sections for the reactions e + e -→ e + e -, e + e -→ µ + µ -, e + e -→ τ + τ - and e + e -→γγ measured at 12 energies around the Z peak and corresponding to about 20 pb-1 of cumulated luminosity. Four-fermion contact term models assuming various chiralities of lepton currents are fitted to the lepton data and lower limits on the energy scale Λ of such terms are set at 95% c.l. The limits vary in the range 0.9 4.7 TeV, depending on the model and on the lepton flavour. The eeγγ contact terms are searched for assuming various chiralities. Limits on the energy scale Λ between 79 and 130 GeV are extracted from the data. The resu…
Measurement of Z-pair production in e(+)e(-) collisions and constraints on anomalous neutral gauge couplings
The ZZ production cross section is measured from a data sample corresponding to a total integrated luminosity of 452 pb−1, collected by the ALEPH experiment at LEP at centre-of-mass energies from 192 to 209 GeV. Individual cross sections, extracted at six centre-of-mass energies, are found to be in agreement with Standard Model calculations. The results are used to set limits on anomalous neutral gauge couplings. The ZZ production cross section is measured from a data sample corresponding to a total integrated luminosity of 452 pb−1 , collected by the ALEPH experiment at LEP at centre-of-mass energies from 192 to 209 GeV. Individual cross sections, extracted at six centre-of-mass energies, …
Measurement of the ratio using event shape variables
Abstract The branching fraction of Z → b b relative to all hadronic decays of the Z has been measured using event shape variables to preferentially select Z → b b events. The method chosen applies a combination of shape discriminators and the selection of high transverse momentum leptons to event hemispheres. From a sample of 440 000 hadronic Z decays collected with the ALEPH detector at LEP, the ration Γ b b Γ had = 0.228±0.005( stat. )±0.005( syst. ) is measured.
An experimental study of γγ → hadrons at LEP
An analysis of γγ interactions has been performed using untagged hadronic data obtained by the ALEPH detector at LEP. The data show at low transverse momentum (pt) are well reproduced by a model based on the vector meson dominance mechinism (VDM). At high pt thrust the presence of hard scattering processes is demonstrated. This component is well described in shape and normalization by a QCD calculation.
Search for Higgs bosons decaying to WW in e(+)e(-) stope collisions at LEP
A search for Higgs bosons produced in association with a fermion pair, and decaying to WW, is performed with the data collected by the ALEPH detector at centre-of-mass energies ranging from 191 to 209 GeV. The data correspond to an integrated luminosity of 453.2 pb^-1. Thirteen exclusive selections are developed according to the different final state topologies. No statistically significant evidence for a Higgs boson decaying into a WW pair has been found. An upper limit is derived, as a function of the Higgs boson mass, on the product of the e+e- -> Hff cross section and the H -> WW branching ratio. The data on the search for H -> WW are combined with previously published ALEPH re…
Search for neutral MSSM Higgs bosons at LEP
The four LEP collaborations, ALEPH, DELPHI, L3 and OPAL, have searched for the neutral Higgs bosons which are predicted by the Minimal Supersymmetric Standard Model (MSSM). The data of the four collaborations are statistically combined and examined for their consistency with the background hypothesis and with a possible Higgs boson signal. The combined LEP data show no significant excess of events which would indicate the production of Higgs bosons. The search results are used to set upper bounds on the cross-sections of various Higgs-like event topologies. The results are interpreted within the MSSM in a number of "benchmark" models, including CP-conserving and CP-violating scenarios. Thes…