Electroweak measurements in electron–positron collisions at w-boson-pair energies at lep

Contains fulltext : 121524.pdf (preprint version ) (Open Access

Search for single top production in e+ e- collisions at s**(1/2) = 189-GeV - 202-GeV

The single top production via flavour changing neutral currents in the reactions ee -> t c/u is searched for in approximately 411 pb-1 of data collected by ALEPH at centre-of-mass energies in the range between 189 and 202 GeV. In total, 58 events are selected in the data to be compared with 50.3 expected from Standard Model backgrounds. No deviation from the Standard Model expectation is observed. A 95\%~CL upper limit of 0.72 pb on the single top production cross section at 202 GeV is derived assuming a top mass of 174 GeV/c^2 and a 100% branching ratio of the top decay into bW. A model dependent limit on the flavour-changing couplings kZ and kg is obtained by combining all centre-of-mass energies

Search for Charged Higgs bosons: Combined Results Using LEP Data

The four LEP collaborations, ALEPH, DELPHI, L3 and OPAL, have searched for pair-produced charged Higgs bosons in the framework of Two Higgs Doublet Models (2HDMs). The data of the four experiments are statistically combined. The results are interpreted within the 2HDM for Type I and Type II benchmark scenarios. No statistically significant excess has been observed when compared to the Standard Model background prediction, and the combined LEP data exclude large regions of the model parameter space. Charged Higgs bosons with mass below 80 GeV/c^2 (Type II scenario) or 72.5 GeV/c^2 (Type I scenario, for pseudo-scalar masses above 12 GeV/c^2) are excluded at the 95% confidence level