Institute of Nuclear Physics,

The data collected at centre-of-mass energies of 188.6 GeV by ALEPH at LEP, corresponding to an integrated luminosity of 176.2 pb− 1, are analysed in a search for pair-produced charged Higgs bosons H±. Three analyses are employed to select the τ+ ν ττ− ν ̄ τ, cs ̄ τ− ν ̄ τ and cs ̄ sc ̄ final states. No evidence for a signal is found. Upper limits are set on the production cross section as a function of the branching fraction B (H+→ τ+ ν τ) and of the mass mH±, assuming that the sum of the branching ratios is equal to one. In the ...

A search for γγ decays of a Higgs boson is performed in the data sample collected at LEP with the ALEPH detector between 1991 and 1999. This corresponds to an integrated luminosity of 672pb− 1 at centre-of-mass energies ranging from 88 to 202GeV. The search is based on topologies arising from a Higgs boson produced in association with a fermion pair via the Higgs-strahlung process e+ e−→ Hf f ̄, with ff ̄= ν ν ̄, e+ e−, μ+ μ−, τ+ τ− or qq ̄. Twenty-two events are selected in the data, while 28 events are expected from standard ...

The data collected in 1998 by ALEPH at LEP at a centre-of-mass energy of 188.6 GeV, corresponding to an integrated luminosity of 176.2 pb��� 1, are analysed to search for invisible decays of a Higgs boson produced in the reaction e+ e������ h Z. The number of events found in the data and their properties are in agreement with the Standard Model expectation. This search results in an improved 95% CL lower limit on the Higgs boson mass of 95.4 GeV/c2, assuming it decays totally invisibly and for a production cross ...

A study of scaling violations in fragmentation functions performed by the ALEPH collaboration at LEP is presented. Data samples enriched in uds, c, b and gluon jets, respectively, together with measurements of the longitudinal and transverse inclusive cross sections are used to extract the fragmentation function for the gluon and for each flavour. The measurements are compared to data from experiments at energies between 22 GeV and 91 GeV and scaling violations consistent with QCD predictions are observed. From ...

The Michel parameters and the average τ-neutrino helicity are measured using correlations between the decays of the τ+ and τ− produced on the Z resonance and observed in the ALEPH detector at LEP. The Michel parameters, ϱl, ηl, ξl,(δξ) l, are determined from τ→ l ν lν τ with l=(e, μ), and the average τ neutrino helicity,〈 h (ντ)〉, from τ→ hν with h=(π, ϱ, a1). The results obtained with e− μ universality are: ϱl= 0.751±0.039±0.022, ηl=− 0.04±0.15±0.11, ξl= 1.18±0.15±0.06,(δξ) l= 0.88±0.11±0.07, and the average τ neutrino ...

An analysis of the properties of hadronic final states produced in electron-positron annihilation at centre-of-mass energies of 130 and 136 GeV is presented. The measurements are based on a data sample of 5.7 pb ^-1 collected in November 1995 with the Aleph detector at LEP. Inclusive charged particle distributions, jet rates and event-shape distributions are measured and the results are compared with the predictions of QCD-based models. From the measured distributions quantities are determined for which the ...

The e+ e−→ W+ W− cross section is measured in a data sample collected by ALEPH at a mean centre-of-mass energy of 172.09 GeV, corresponding to an integrated luminosity of 10.65 pb− 1. Cross sections are given for the three topologies, fully leptonic, semi-leptonic and hadronic of a W-pair decay. Under the assumption that no other decay modes are present, the W-pair cross section is measured to be 11.7±1.2 (stat.)±0.3 (syst.) pb. The existence of the triple gauge boson vertex of the Standard Model is clearly preferred by ...

A search for selectron, smuon and stau pair production is performed with the data collected by the ALEPH detector at LEP at centre-of-mass energies up to 209 GeV. The numbers of candidate events are consistent with the background predicted by the Standard Model. Final mass limits from ALEPH are reported.

The 132 pb ^-1 of data collected by ALEPH from 1991 to 1994 have been used to analyze η and ω production in τ decays. The following branching fractions have been measured: B (τ^-→ τ ω h^-) &= & (1.91 ± 0.07 ± 0.06) * 10^-2,\ B (τ^-→ τ ω h^-π^ 0) &= & (4.3 ± 0.6 ± 0.5) * 10^-3,\ B (τ^-→ τ η K^-) &= & (2.9^+ 1.3 _-1.2 ± 0.7) * 10^-4,\ B (τ^-→ τ η h^-π^ 0) &= & (1.8 ± 0.4 ± 0.2) * 10^-3 and the 95% CL limit B(τ^-→τηπ^-)<6.2*10^-4 has been obtained. The ωπ^- and ηπ^-π^0 rates and dynamics are found in agreement with the predictions made ...

An improved search for B 0 s oscillations is performed in the ALEPH data sample collected during the first phase of LEP, and reprocessed in 1998. Three analyses based on complementary event selections are presented. First, decays of B 0 s mesons into hadronic flavour eigenstates are fully reconstructed. This selection yields a small sample of candidates with excellent decay length and momentum resolution and high average B 0 s purity. Semileptonic decays with a reconstructed D− s meson provide a second sample ...

Abstract: Using about 950 000 hadronic events collected during 1991 and 1992 with the ALEPH detector, the ratios rb= alpha bs udsc s and r uds= alpha uds s cb s have been measured in order to test the flavour independence of the strong coupling constant alpha s. The analysis is based on event-shape variables using the full hadronic sample, two b-quark samples enriched by lepton tagging and lifetime tagging, and a light-quark sample enriched by lifetime antitagging. The combined results are rb= 1.002+/-0.023 and r uds= 0.971+/- ...

Abstract: The inclusive production of the omega (782) vector meson in hadronic Z decays is measured and compared to model predictions. The analysis is based on 4 million hadronic Z decays recorded by the ALEPH detector between 1991 and 1995. The production rate for x_p= p_meson/p_beam> 0.05 is measured in the omega-> pi^+ pi^-pi^ 0 decay mode and found to be 0.585+-0.019 _stat+-0.033 _sys per event. Inclusive eta meson production is also measured in the same decay channel for x_p> 0.10, obtaining 0.355+-0.011 _stat+- ...