Measurement of W-pair production in e+e−e^+ e^- collisions at 189 GeV

The production of W-pairs is analysed in a data samplecollected by ALEPH at a mean centre-of-mass energy of 188.6 GeV,corresponding to an integrated luminosity of 174.2 pb^-1. Crosssections are given for different topologies of W decays intoleptons or hadrons. Combining all final states and assumingStandard Model branching fractions, the total W-pair cross sectionis measured to be 15.71 +- 0.34 (stat) +- 0.18 (syst) pb.Using also the W-pair data samples collected by ALEPH at lowercentre-of-mass energies, the decay branching fraction of the W bosoninto hadrons is measured to be BR (W hadrons) = 66.97+- 0.65 (stat) +- 0.32 (syst) %, allowing a determination of theCKM matrix element |V(cs)|= 0.951 +- 0.030 (stat) +- 0.015 (syst)

Search for γγ→ηb\gamma\gamma \rightarrow \eta_b in e+e−e^{+}e^{-} collisions at LEP2

A search for the pseudoscalar meson eta_b is performed in two-photon interactions at LEP~2 with an integrated luminosity of 699 pb^-1 collected at e+e- centre-of-mass energies from 181 GeV to 209 GeV. One candidate event is found in the six-charged-particle final state and none in the four-charged-particle final state, in agreement with the total expected background of about one event. Upper limits of Gamma_gammagamma(eta_b) * BR(eta_b -> 4 charged particles) 48 eV Gamma_gammagamma(eta_b) * BR(eta_b -> 6 charged particles) 132 eV are obtained at 95\% confidence level, which correspond to 95\% confidence level upper limits of $9.0\%$ and $25\%$ on these branching ratios

A Study of the decay width difference in the B0(s) - anti-B0(s) system using phi phi correlations

In a data sample of about four million hadronic Z decays recorded with the ALEPH detector from 1991 to 1995, the $B^{0}_{s} \to D^{(*)+}_{s}D^{(*)-}_{s}$ decay is observed, based on tagging the nal state with two $\phi$ mesons in the same hemisphere. The $D^{(*)+}_{s}D^{(*)-} _{s}$ final state is mostly CP even and corresponds to the short-lived $B^0$ mass eigenstate. The branching ratio of this decay is measured to be BR$(B^{0}_{s}(short) \to D^{(*)+}_{s}D^{(*)-}_{s}) = (23\pm 10^{+19}_{-9})$. A measurement of the lifetime of the $B^0$(short) gives 1.27$\pm$ 0.33$\pm$ 0.07 ps. The lifetime and branching ratio measurements allow two essentially independent estimates to be made of the relative decay width difference $\Delta\Gamma/\Gamma$ in the $B^{0}_{s}-\overline{B}^{0}_{s}$ system, corresponding to an average value $\Delta\Gamma/\Gamma = (25^{+21}_{-14})%

Search for the neutral Higgs bosons of the Standard Model and the MSSM in e(+)e(-) collisions at root s=189 GeV

Neutral Higgs bosons of the Standard Model and of the MSSM are searched for in the data collected at a centre-of-mass energy of 188.6GeV by the ALEPH experiment at LEP, with an integrated luminosity of 176 pb(-1). No evidence for a signal is found. A lower limit of 92.9GeV/c(2) at 95% confidence level is set on the mass of the Standard Model Higgs boson, with an expected sensitivity of 95.9 GeV/c(2). In the MSSM, for tan beta greater than or equal to 0.7 and for benchmark parameter choices, observed (expected) lower limits of 82.5 (83.1) GeV/c(2) and 82.6 (83.2) GeV/c(2) are derived for the masses of the neutral Higgs bosons h and A, respectively. An update of the general MSSM parameter scan is also presented

Measurement of the W mass and width in e+ e- collisions at 189-GeV

The mass of the W boson is determined in e + e − collisions at LEP by the direct reconstruction of W decays in WW→qq¯qq¯ and WW→ℓνqq¯ events, supplemented by measurements using the kinematic properties of the leptons in the \mathrm{W}\mathrm{W}\rightarrow\mbox{\ell\nu }\mbox{$\ell\nu$} decay channel. The main sample of W pairs is selected from an integrated luminosity of 174 pb −1 collected with the ALEPH detector in 1998 at a centre-of-mass energy of 188.63 GeV. The combined result from all channels is mW=80.432±0.072(stat.)±0.041(syst.)±0.019(FSI)±0.017(LEP)GeV/c2, where FSI represents the possible effects of final state interactions in the qq¯qq¯ channel. In a second two-parameter fit to the qq¯qq¯ , \mathrmeνqq¯ and μνqq¯ channels, where the W mass and width are decoupled, the average W width is found to be { 2.24±0.20(stat.)±0.13(syst.) GeV/ c2 }, consistent with the Standard Model prediction. The combination of the mass measurement presented in this paper together with those derived previously from the W pair cross section at 161 and 172 GeV and direct reconstruction at 172 and 183 GeV gives mW=80.418±0.061(stat.)±0.040(syst.)±0.019(FSI)±0.017(LEP)GeV/c2