Inclusive production of the η\eta and ω\omega mesons in Z decays, and the muonic branching ratio of the ω\omega

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 +- 0.024_sys per event. The branching ratio for omega -> mu^+ mu^- is investigated. A total of 18.1 +- 5.9 events are observed, from which the muonic branching ratio is measured for the first time to be BR(omega -> mu^+ mu^-) = (9.0 +- 2.9_stat +- 1.1_sys)*10^-5

Search for anomalous weak dipole moments of the τ\tau lepton

The anomalous weak dipole moments of the $\tau$ lepton are measured in a data sample collected by ALEPH from 1990 to 1995 corresponding to an integrated luminosity of 155~pb$^{-1}$. Tau leptons produced in the reaction $e^+ e^- \rightarrow \tau^+ \tau^-$ at energies close to the ${\rm Z}$ mass are studied using their semileptonic decays to $\pi$, $\rho$, $a_1 \rightarrow \pi 2\pi^0$ or $a_1 \rightarrow 3 \pi$. The real and imaginary components of both the anomalous weak magnetic dipole moment and the CP-violating anomalous weak electric dipole moment, ${\rm Re}\,\mu_{\tau}$, ${\rm Im}\,\mu_{\tau}$, ${\rm Re}\,d_{\tau}$ and ${\rm Im}\,d_{\tau}$, are measured simultaneously by means of a likelihood fit built from the full differential cross section. No evidence of new physics is found. The following bounds are obtained (95\% CL): $|{\rm Re}\, \mu_{\tau} | 1.14 \times 10^{-3}$, $|{\rm Im}\, \mu_{\tau} | 2.65 \times 10^{-3}$, $|{\rm Re}\, d_{\tau} | 0.91 \times 10^{-3}$, and $|{\rm Im}\, d_{\tau} | 2.01 \times 10^{-3}$

Search for Single Top Production in e+e−e^{+} e^{-} Collisions at s\sqrt{s} up to 209 GeV

Single top production via the flavour changing neutral current reactions e+e- -> \bar{t}c , \bar{t}u is searched for within the 214~pb-1 of data collected by ALEPH at centre-of-mass energies between 204 and 209~GeV. No deviation from the Standard Model expectation is observed and upper limits on the single top production cross sections are derived. The combination with data collected at lower centre-of-mass energies yields an upper limit on the branching ratio BR(t -> Zc)+BR(t -> Zu) 14%, for BR(t -> \gamma c)+BR(t -> \gamma u)= 0 and mt=174 GeV/c2$

A measurement of the gluon splitting rate into cc‾c\overline{c} pairs in hadronic Z decays

The rate of gluons splitting into $c \bar{c}$ pairs in hadronic $Z$ decays is measured using the data sample collected by ALEPH from 1991 to 1995. The selection is based on the identification of leptons (electrons and muons) originating from semileptonic charm decays, and on the topological properties of signal events. The result derived from the selected sample is $g_{c \bar{c}}=(3.26 \pm 0.23 \rm{(stat)} \pm 0.42 \rm{(syst)}) %

Single- and multi-photon production in e+e−e^+ e^- collisions at s\sqrt{s} up to 209 GeV

Events containing only energetic photons are analysed in a sample of 628 pb -1 of data recorded from e+e- collisions at centre-of-mass energies between 189 and 209 GeV by the ALEPH detector at LEP. The \reenunug and \reeggg cross sections are measured and found to be in agreement with the Standard Model predictions. The number of light neutrino generations is determined to be N_\nu = 2.86 \pm 0.09. Upper limits are derived on the cross sections for photon production in the context of several supersymmetric models. Limits are also set on the parameters of models with extra spatial dimensions with contact interactions and with excited electrons

Measurement of the inclusive D^{*{\pm}}productionin production in \gamma\gamma$ collisions at LEP

The inclusive production of D$^{*\pm}$ mesons in two-photon collisions is measured with the ALEPH detector at \epem centre-of-mass energies from 183\unit{GeV} to 209\unit{GeV}. A total of $360 \pm 27$ D$^{*\pm}$ meson events were observed from an integrated luminosity of 699\unit{pb^{-1}}. Contributions from direct and single-resolved processes are separated using the ratio of the transverse momentum p_{\rmt}^{\rm D^{*\pm}} of the D$^{*\pm}$ to the visible invariant mass $W_{\mathrm{vis}}$ of the event. Differential cross sections of D$^{*\pm}$ production as functions of $p_{\rm t}^{\rm D^{*\pm}}$ and the pseudorapidity $|\eta^{\rm D^{*\pm}}|$ are measured in the range 2\unit{GeV}/c p_{\rm t}^{\rm D^{*\pm}} 12\unit{GeV}/c and $|\eta^{\rm D^{*\pm}}| 1.5$. They are compared to next-to-leading order (NLO)perturbative QCD calculations. The extrapolation of the integrated visible D$^{*\pm}$ cross section to the total charm cross section, based on the Pythia Monte Carlo program, yields \sigma ( \epem \rightarrow \epem \ccbar ) _ { \sqrt{s} =197\unit{GeV} } = 731 \pm 74_{\mathrm{stat}} \pm 47_{\mathrm{syst}} \pm 157_{\mathrm{extr}} \unit{pb}

Single- and multi-photon production in e+e−e^+ e^- collisions at s\sqrt{s} up to 209 GeV

Events containing only energetic photons are analysed in a sample of 628 pb -1 of data recorded from e+e- collisions at centre-of-mass energies between 189 and 209 GeV by the ALEPH detector at LEP. The \reenunug and \reeggg cross sections are measured and found to be in agreement with the Standard Model predictions. The number of light neutrino generations is determined to be N_\nu = 2.86 \pm 0.09. Upper limits are derived on the cross sections for photon production in the context of several supersymmetric models. Limits are also set on the parameters of models with extra spatial dimensions with contact interactions and with excited electrons